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Conferences & Courses
13–18 February 2016
9726: Solid State Lasers XXV: Technology and Devices . . . . . . . . . . . .3
9727: Laser Resonators, Microresonators, and Beam
Control XVIII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
9728: Fiber Lasers XIII: Technology, Systems, and Applications . . .38
9729: High Energy/Average Power Lasers and Intense Beam
Applications IX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
9730: Components and Packaging for Laser Systems II . . . . . . . . . . .74
9731: Nonlinear Frequency Generation and Conversion:
Materials, Devices, and Applications XV . . . . . . . . . . . . . . . . . . 86
9732: Real-time Measurements, Rogue Events, and Emerging
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
9733: High-Power Diode Laser Technology and
Applications XIV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106
SYMPOSIUM CHAIRS:
Guido Hennig,
Daetwyler Graphics
AG (Switzerland)
Yongfeng Lu,
Univ. of
Nebraska-
Lincoln (USA)
SYMPOSIUM CO-CHAIRS:
Reinhart Poprawe
Fraunhofer-Institut für
Lasertechnik (Germany)
Koji Sugioka
RIKEN (Japan)
9735: Laser Applications in Microelectronic and Optoelectronic
Manufacturing (LAMOM) XXI . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
9736: Laser-based Micro- and Nanoprocessing X . . . . . . . . . . . . . . . 139
9737: Synthesis and Photonics of Nanoscale Materials XIII . . . . . . . 155
9738: Laser 3D Manufacturing III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160
9739: Free-Space Laser Communication and Atmospheric
Propagation XXVIII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
9740: Frontiers in Ultrafast Optics: Biomedical, Scientific, and
Industrial Applications XVI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
9741: High-Power Laser Materials Processing: Lasers, Beam
Delivery, Diagnostics, and Applications V . . . . . . . . . . . . . . . . 196
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9726-1, Session 1
Ian F . Elder, Daniel H . Thorne, Robert A . Lamb, Selex ES
Ltd . (United Kingdom); Richard M . Jenkins, HollowGuide
Ltd . (United Kingdom)
High brightness laser sources operating in the mid-infrared (wavelengths
2-5 µ m) region of the electromagnetic spectrum are of interest for a wide range of applications encompassing medical, defence and remote sensing.
A compact, rugged, low-loss beam combiner for combining four wavelengths covering the wavelength range 2.1 µ m to 4.6 µ m has been designed, manufactured and characterised. The beam combiner consisted of a series of dichroic components integrated into a hollow waveguide optical circuit for confining, combining and directing the optical beams from four discrete waveguide input ports to a common output port. By coupling each wavelength into the fundamental mode of the waveguide circuit, common boresight of the combined wavelengths was achieved. Precision CNC milling techniques have been used to manufacture the hollow waveguide circuit and the alignment slots for the dichroic components, in a common Macor substrate.
4.2 W of combined output power from three quantum cascade lasers
(QCLs) and a thulium fibre laser pumped Ho:YAG laser was demonstrated, with an overall transmission for the hollow waveguide beam combiner
(HWBC) optical circuit of 93%. Propagation losses in the waveguide sections were negligible. The major contributor to the overall loss was the performance of the dichroic optics for the near diffraction-limited beams used here.
The four wavelengths were co-boresighted to better than 20 µ rad in the common output beam exiting the HWBC optical circuit. The performance of the HWBC optical circuit was measured to be insensitive to lateral and angular misalignments typical for operation over a wide temperature range.
resonator configuration, allowing for stable operation from 0-10% dutycycle. To demonstrate the possibilities, a fiber coupling by standard optics into a 200 µ m, 0.2NA GeO2-fiber has been shown. A high optical average power of 30W and energy of up to 200mJ within 300 µ s pulses were sent through the fiber without any damage. The coupling efficiency of about 70% was shown to be limited only by the fiber itself.
9726-3, Session 1
Evgeny Slobodchikov, IPG Photonics Corp . (United States);
Logan R . Chieffo, Kevin F . Wall, Q-Peak, Inc . (United
States)
Q-Peak Inc. has developed a Cr:ZnSe based femtosecond oscillator – power amplifier laser operating in the 2.5 ?m region. The system generates 1 mJ per pulse at a 1-kHz repetition rate with a pulse duration of 184 fs, corresponding to a peak power of 5 GW. To the best of our knowledge this represents a record power for this spectral region. The high-peak power source utilizes a hybrid laser architecture, combining efficient fiber-laser pumping of solid state crystals. A Tm:fiber laser pumped, SEASAMinitiated, Cr:ZnSe femtosecond oscillator provides a seed for chirped pulse amplification. 50-fs pulses from the oscillator are stretched in a grating pulse stretcher and then amplified in a chain consisting of a regenerative amplifier and two stages of linear amplifiers all based on Cr:ZnSe. The pump power for the amplification is provided by a Q-switched, high repetition rate,
Ho:YLF laser, which in turn, is pumped by a high power Tm:fiber laser. The amplified pulses are compressed by a grating pulse compressor, resulting in
1 W of average power at a 1-kHz repetition rate. This laser system represents the state-of-the-art in short-pulse duration, pulse energy, and beam quality in this IR spectral range.
9726-2, Session 1
µ
Manuel Messner, Arne Heinrich, Clemens Hagen, Pantec
Engineering AG (Liechtenstein); Karl Unterrainer,
Technische Univ . Wien (Austria)
Over the last two decades, the need for diode pumped solid state (DPSS) lasers has increased drastically due to their obvious advantages of mainly stability and ruggedness, compared to conventional flash-lamp systems.
Of special interest is Er:YAG as a crystal material since light at 2.94
µ m is emitted, coinciding with a major water absorption line. This allows the presented laser system to efficiently cut hard and soft biological tissue for future medical applications, and, furthermore, industrial applications like glass cutting are now within reach.
We demonstrated a monolithic high-power DPSS Er:YAG laser at 2.94
µ m with average output power of up to 50W and pulse energy beyond 300mJ in 300 µ s pulses. The high peak power of nearly 1kW is delivered in a high quality beam (M?<15), maintained over a large cooling water temperature range of 18-25°C. These results present a twofold increase in average output power and a threefold increase in pulse energy over the prior laser design as well as a decrease in laser threshold. The enabling step was an optimized
FEM simulation of the thermal lensing effect resulting in an improved
9726-4, Session 1
Chris DePriest, Nadia Baranova, Ken Stebbins, Ilya
Bystryak, Michael Rayno, Rui Pu, Kevin Ezzo, Q-Peak, Inc .
(United States)
Q-Peak has demonstrated a novel, compact, pulsed eyesafe laser architecture operating with >15 mJ pulses at repetition rates over 150 Hz.
The design leverages an end-pumped solid-state laser geometry to produce better eyesafe beam quality (<7 mm-mrad), and also provides a path to more scalable laser system architectures, covering a wide range of eyesafe applications.
The laser consists of an actively Q-switched oscillator cavity which utilizes an end-pumped Nd:YAG gain medium, and a Rubidium Titanyl Phosphate
(RTP) electro-optical crystal to produce pulse-widths <20 ns. The oscillator provides an effective front-end-seed to the optical parametric oscillator
(OPO), which utilizes Potassium Titanyl Arsenate (KTA) in a ring-cavity
OPO geometry. This OPO geometry efficiently converts pump photons into the eyesafe band with minimal degradation in beam quality, allowing this laser architecture to provide an attractive path to high-power eyesafe pulse energies compared to traditional systems utilizing Potassium Titanyl
Phosphate (KTP). The laser system has been designed to fit within a volume of less than 2450 cc.
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Conference 9726:
Solid State Lasers XXV: Technology and Devices
9726-5, Session 1
Brian Cole, Alan D . Hays, Nathaniel Hough, John Nettleton,
Lew Goldberg, U .S . Army RDECOM CERDEC NVESD
(United States)
Compact, low cost Q-switched lasers in the eye-safe 1.5
µ m regime are required for LADAR, range-finding and laser pointing. In this paper, we describe a compact, side-pumped, Er/Yb glass laser with a low cost mechanical Q-switch. The Q-switch uses a mirror or reflecting prism mounted on a cantilever resonant spring that is driven by a small electromagnetic coil. The electromagnetic drive principle is the same as used in haptic devices that produce a tactile response in cell phones.
The mechanical Q-switch offers the advantages of negligible optical loss, low cost, and operation with a prism reflector to achieve resonant cavity stability. The demonstrated laser used a 5 mm long Er/Yb glass gain element with AR coating on one facet and a 90% reflective coating on the second facet for the cavity output coupler. The glass was side-pumped by a 940 nm, 5 mm wide diode bar generating up to 100 W peak power, and operated for a duration of 3 ms at 1-5 Hz. Laser cavity lengths were in the
25-40 mm range. Target energies of 5mJ have been realized, with pulse widths of 20-25ns, and an optical-to-optical efficiency of greater than 2%.
Lasers were operated in TEM00 mode with a near-diffraction limited beam divergence of 2.5 mRad. Laser operation was explored as a function of pulse repetition frequency; and modeling was performed to understand the interplay between the thermal loading of the glass during optical pumping and the resultant time dependent thermal lensing and cavity mis-alignment.
9726-7, Session 2
µ
Yongguang Zhao, Weichao Yao, Deyuan Shen, Jiangsu Key
Lab . of Advanced Laser Materials (China)
Extension of laser wavelength is the direction of researcher’s consistent efforts, especially for the eye-safe band due to its unique applications in in lidar, remote sensing, guidance, and free-space optical communication.
Now, widely tunable Raman fiber laser from ~1620 nm to ~1720 nm has been demonstrated using a home-made Er,Yb fiber as pump source and volume
Bragg grating as wavelength selector. The output power in the whole wave-band could easily reach ten watt level, which means this scheme is an effect way to obtain high power output with high enough pump power and suitable thermal management. This Raman fiber laser would have promising applications in various fields, such as remote sensing, medicine treatment, photoacoustic imaging system for deep tissue imaging, as an effect pump source for Cr2+, or Dy3+ doped laser gain medium, etc.
9726-8, Session 2
Wei Zhou, Li Wang, Haitao Huang, Yongguang Zhao,
Deyuan Shen, Jian Zhang, Dingyuan Tang, Jiangsu Key
Lab . of Advanced Laser Material (China)
9726-6, Session 1
Haro Fritsche, DirectPhotonics Industries GmbH
(Germany) and Technische Univ . Berlin (Germany); Oliver
Lux, Martin Gaertner, Technische Univ . Berlin (Germany);
Andreas Grohe, Wolfgang Gries, DirectPhotonics Industries
GmbH (Germany); Hans Joachim Eichler, Technische Univ .
Berlin (Germany)
In recent years, compact diode pumped ~3-?m solid-state laser have attracted considerable attention due to their powerful laser radiation directly from handheld device without using costly IR-fibers and applications in military countermeasures, remote sensing, atmosphere pollution monitoring, medical. We have recently reported continue-wave (CW) laser operations with Er:Lu2O3 and Er:Y2O3 ceramics as gain mediums. With a simple planparallel cavity, maximum output powers of of 610 mW and 320 mW have been achieved respectively. In some specific biomedical applications, wattlevel CW radiation is required. Now, a systematic investigation on a series of
Er-doped Lu2O3 and Y2O3 ceramics with different dopant concentrations
(CEr = 3at.%–15at.%) was presented. By designing laser resonator and selecting reasonable ceramic lengths, the maximum output powers of
1.4 W and 2.1 W have been achieved with Er:Lu2O3 and Er:Y2O3 ceramic, respectively. The corresponding slope efficiencies were 11.9% and 11.0%. The prospects for improvement in output power and lasing efficiency via further optimization in Er3+-doping concentration are considered.
Resonantly pumped Er:YAG lasers at 1645 nm or 1617 nm are of interest for developing laser transmitters that are suitable for CO2 and CH4 LIDAR applications. These laser sources are characterized by a high quantum efficiency, since the corresponding pump and lasing processes involve different Stark sub-levels of the 4I13/2 and 4I15/2 electronic states. We report the characterization of resonantly pumped Er:YAG lasers that were pumped by both broadband and narrowband diode lasers at 1470 and 1532 nm. As the erbium absorption lines are very narrow, higher efficiency of the
Er:YAG laser is demonstrated when using narrowband pump lasers. Further increase in efficiency was realized by utilizing a pump source at 1532 nm instead of 1470 nm due to the lower quantum defect. Here, we measured a slope efficiency of about 70 % which is comparable to fiber laser pumping.
In Q-switched mode, pulse durations of about 60 ns were obtained which is ideal for LIDAR applications. In addition, two narrowband diode laser modules incorporating volume Bragg gratings were combined to a dualwavelength pump source, providing a power of 80 W out of a 200 µ m fiber. Compared to single-wavelength pumping, we observed a significant increase in output power as well as a reduction of the laser threshold.
Hence, multi-wavelength pumping employing wavelength-stabilized diode lasers offers the possibility to develop a compact and highly efficient laser transmitter which meets the strict requirements of a satellite-borne methane
LIDAR system in terms of weight and volume while ensuring very low power consumption.
9726-10, Session 3
Vesna Markovic, Andreas Rohrbacher, Peter Hofmann,
Wolfgang Pallmann, Simonette Pierrot, Lumentum
(Switzerland); Bojan Resan, Lumentum (Switzerland) and Univ . of Applied Sciences and Arts Northwestern
(Switzerland)
Single crystal fibers (SCF) represent an alternative technology for ultrashort pulse amplification to high average power in a simple architecture. SCF have an aspect ratio of a short rod fiber or a thin and long crystal and benefit several advantages from the both concepts. Relatively short interaction length and large signal beam diameter mitigate the nonlinear effects and allow direct amplification of femtosecond pulses avoiding the standard
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Conference 9726:
Solid State Lasers XXV: Technology and Devices chirped pulse amplification (CPA) technique.
In this paper, we demonstrate the amplification of femtosecond pulses up to 160 W of average power using a compact and simple two-stage SCF amplifier without CPA. High brightness pumping and a double-pass signal configuration of the first stage allowed us to reach the small signal gain value of 32.5 dB, i.e. almost 2000, which is the highest reported value.
Additionally, we implemented for the first time the bidirectional pumping scheme in the second stage. With the total pump power of 300 W, we achieved the highest average power of femtosecond pulses and the highest extraction efficiency from the SCF, i.e. 160 W and 42 %, respectively. The pulse duration at the maximum output power was measured to be 800 fs assuming sech2 temporal shape. The amplification details and spectral, temporal and spatial characterization of the output beam will be presented.
guided inside, thus flood–illuminating the gain medium, but the signal is in a free propagation mode inside it. Presented here are the new laser experimental results with the diode-pumped Yb:YAG SCFs fabricated by laser-heated pedestal growth (LHPG) technique. The YAG SCFs Yb-doped at 10%, 6% and 1% level with diameters of 100 µ m and 50 µ m and maximum length of 100 mm were studied. A 200-W diode laser module (DLM) was used to pump the SCFs. The DLM‘s output wavelength was tunable from
960 nm to 980 nm, and was selected for each experiment depending on the SCF length and Yb doping concentration. The absorption and emission spectrum of each fiber were characterized and the insertion loss and small signal gain of each fiber were measured. The observed difference in lasing performance between the SCF laser in a free propagation mode and the SCF laser in a waveguiding mode of operation is thoroughly discussed.
9726-11, Session 3
Fabien Lesparre, Jean-Thomas Gomes, Xavier Delen,
Institut d’Optique Graduate School (France); Igor Marial,
Julien Didierjean, FiberCryst S .A .S . (France); Wolfgang
Pallmann, Lumentum (Switzerland); Bojan Resan,
Lumentum (Switzerland) and Univ . of Applied Sciences and Arts Northwestern (Switzerland); Frederic Druon,
François Balembois, Patrick Georges, Institut d’Optique
Graduate School (France)
Yb-doped diode-pumped solid-state lasers in MOPA configuration clearly dominate the field of high average-power ultrafast lasers. Among the geometries used so far for high-power Yb-doped DPSSL as slabs, rods and thin disks, the single-crystal-fiber technology (SCF) was recently shown to have a high potential for the amplification of high average and peak power pulses thanks to a very efficient thermal management and high optical efficiencies.
We present the use of Yb:YAG SCFs for high-energy picosecond-pulse amplification. As a seed, we used a passively modelocked Yb-YAG oscillator delivering 8.5-ps pulses at 500 kHz with an average power of 25 mW at 1030 nm. The amplifier consists of two double-pass SCF stages. The first amplification stage is optimized to provide high gain. Up to 8 W are obtained after amplification in a 30 mm long 2 at. % doped Yb:YAG SCF pumped with a 100 W high brightness laser diode, corresponding to a high optical gain of 25 dB. In order to achieve higher extraction levels, a 969 nm laser diode delivering 200 W is used for the second stage. Furthermore, to reduce the peak power and prevent Kerr lensing, the divided-pulseamplification technic is implemented. It consists of creating several temporal replicas seeded in a double-pass amplifier and passively recombined into single, high power pulses. The output power extracted from the second amplifier is 45 W and the pulse energy reaches 90 µ J with a combining efficiency above 96% and a peak power of 11 MW.
9726-12, Session 3
Jun Zhang, U .S . Army Research Lab . (United States);
Youming Chen, U .S . Army Research Lab (United States);
Mark Dubinskii, U .S . Army Research Lab . (United States);
Gisele Maxwell, Shasta Crystals (United States)
Single crystal fiber (SCF), as most often used in the literature today, is the term referring to a pretty thin (usually < 800 µ m dia.) air-clad singlecrystalline gain element in laser configuration where the pump power is
9726-13, Session 3
Subhabrata Bera, Craig D . Nie, James A . Harrington,
Rutgers, The State Univ . of New Jersey (United States);
Stephen C . Rand, Ayan A . Chakrabarty, Theresa Chick,
James Chapman, Stephen Trembath-Reichert, Univ . of
Michigan (United States)
Rare-earth doped single-crystal (SC) Yttrium Aluminum Garnet (YAG) fibers are excellent candidates for high power lasers. These SC fiber optics combine the favorable low Stimulated Brillouin Scattering (SBS) gain coefficient and excellent thermal properties to make them an attractive alternative to glass fiber lasers and amplifiers. Various rare-earth doped
SC fibers have been grown using the laser heated pedestal growth (LHPG) technique. Several cladding methods, including in-situ and post-growth cladding techniques, are discussed in this paper. A rod-in-tube approach has been used by to grow a fiber with an Erbium doped SC YAG fiber core inserted in a SC YAG tube. The result is a radial gradient in the distribution of rare-earth ions. Post cladding methods include sol-gel deposited polycrystalline cladding and the growth of a crystalline cladding layer using a hydrothermal technique.
9726-14, Session 3
Zhaojun Liu, Sasa Zhang, Xingyu Zhang, Yang Liu,
Zhenhua Cong, Shandong Univ . (China)
High power continuous wave Nd:YAG single crystal fiber laser is demonstrated with an output wavelength of 1064 nm. A continuous wave
808-nm diode was employed as the end pumping source. The gain medium was a Nd:YAG crystal fiber (0.2 at.% Nd-doped) with a diameter of 1 mm and a length of 50 mm. It was welded in copper that was water-cooled with the temperature setting at 18 oC. The beam waist diameter of the pumping wave was 800 um inside the crystal fiber.
We studied the absorption rate of the crystal fiber with the highest incident diode power of 162 W. Several input mirrors and output couplers with different radius of curvature (ROC) were examined for pursuit of higher output power. Also output couplers with different transmissions were tried.
The resonating cavity was also simulated with LASCAD. As a result, the highest output power of up to 72.3 W was obtained from a concave-concave cavity. The input mirror was a plano-concave mirror with a ROC of 500 mm.
The output coupler was also a plano-concave mirror with a ROC of 100 mm.
It had a transmission of 50% at 1064 nm. The optical to optical conversion efficiency was up to 61.8% with an absorbed diode power of 117 W. The beam quality factors (M2) were determined to be 20 and 22 in horizontal and vertical directions, respectively. Through intracavity frequency doubling by KTiOPO4 crystal, we also obtained 9.8 W of 532 nm green laser.
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Conference 9726:
Solid State Lasers XXV: Technology and Devices
9726-15, Session 3
Dongsheng Yuan, Zhitai Jia, Yang Li, Baiyi Wu, Xutang Tao,
Shandong Univ . (China)
9726-17, Session 4
Wade Collins, Ryan Feeler, Faming Xu, Mark Kushina,
Northrop Grumman Cutting Edge Optronics (United
States)
Single crystal fiber (SCF) combines the excellent instinct properties of conventional bulk laser crystals, and the special geometry advantage of active optical fibers. YAG and LuAG belong to cubic crystal structure, with good thermal conductivity of 10.7 and 8 W·m?1·K?1, respectively. Despite lower thermal conductivity, LuAG crystal is easier to obtain homogeneous optical quality. Both of them are proper host candidates for single crystal fiber. Recently there are basically two different methods for fabricating crystal fibers: laser heated pedestal growth (LHPG) and micro-pullingdown (?-PD). In comparison with LHPG, ?-PD has much smaller thermal gradient, and here we use ?-PD to carry out high quality SCFs. Through the
?-PD setup manufactured by ourselves, crystal fibers with diameters of ?1 mm and ?800 ?m have been grown successfully. Moreover, some furnace modifications were made to realize the constant crystal diameter for thinner fibers. The crystalline quality and homogeneity along the whole fiber were investigated. The influences of different growth conditions on the crystal fibers will also be discussed.
We describe the design, development and testing of an injection seeded, pulsed, diode pumped, third harmonic Nd:YAG laser that is ruggedized for high energy Doppler LIDAR applications from ground based and airborne platforms. The laser described is specifically designed to provide stable Single Longitudinal Mode (SLM) performance while operating in challenging thermal and vibration environments. Test data is shown of the third harmonic (355 nm) output of > 65 mJ per pulse, operating at 30 Hz, while undergoing thermal and vibrational environmental testing. Data is also shown to support the scalability of this laser technology to 355 nm pulse energies > 100 mJ at laser repetition rates of > 100 Hz.
9726-18, Session 4
Ti Chuang, Joe Hansell, Tim Shuman, Tom Schum, Kent
Puffenberger, Ralph Burnham, Fibertek, Inc . (United
States)
9726-16, Session 4
Upendra N . Singh, Mulugeta Petros, Tamer F . Refaat, NASA
Langley Research Ctr . (United States); Hyung R . Lee, Karl
D . Reithmaier, Science System & Applications, Inc . (United
States); Charles W . Antill Jr ., Jirong Yu, NASA Langley
Research Ctr . (United States)
Water vapor and carbon dioxide are the most dominant greenhouse gases directly contributing to the Earth’s radiation budget and global warming.
Researchers at NASA Langley Research Center are developing a stateof-the-art fully conductively-cooled, end-pumped, triple-pulse 2-micron
Ho:Tm:YLF laser transmitter, as part of the integrated path differential absorption (IPDA) lidar system, for simultaneous and independent monitoring of atmospheric water vapor and carbon dioxide column from an airborne platform. The Ho:Tm:YLF crystal is chosen for its capability to produce a succession of Q-switched pulses from a single pump pulse. For
50 Hz pump pulse repetition rate, the 2 ?m triple-pulse rate is equivalent to 150 Hz. The benefit of generating multiple pulses is facilitated by the combination of long thulium (Tm) upper lifetime and the co-doping of Tm and Holmium (Ho) in YLF. The 792 nm pump laser excites the Tm from
3H6 to 3H4 level. The 3F4, which pumps the Ho, gets two atoms excitation for every excited atom that decays from the 3H4 level. This “two for one” efficiency is one of the features that make this crystal attractive for triple-pulsing. The 2 ?m laser is produced by the Ho 5I7 to 5I8 transition pumped by Tm. The long lifetime of Tm results in the repopulation of Ho after every Q-switch pulse. The energy for the second and third pulse is then extracted by simply reopening the Q-switch every 200 microseconds after the first Q-switch pulse. For a single pump pulse of 5 milliseconds, the laser is targeted to produce three successive injection locked pulses of three different wavelengths, separated by 200 microseconds, with respective pulse energy of 50, 15, and 5 mJ at 50 Hz. Detail design and performance of an end-pumped, tripled-pulsed, injection seeded, conductively-cooled
2-micron Ho:Tm:YLF laser will be presented.
Fibertek has demonstrated a dual-wavelength narrow linewidth UV laser source for NASA airborne ozone DIAL remote sensing application (Global
Ozone Lidar Demonstrator). The application requires two narrow linewidth lasers in the UV region between 300 nm and 320 nm with at least 12 nm separation between the two wavelengths. Each UV laser was based on a novel ring structure incorporating an optical parametric oscillator (OPO) and a sum frequency generator (SFG). The fundamental pump source of the UV laser was a single frequency 532 nm laser, which was frequencydoubled from a diode-pumped, injection-seeded single frequency Nd:YAG laser operating at 1064 nm and 50 Hz repetition rate. The ring frequency converters generated UV wavelengths at 304 nm and 316 nm respectively.
The demonstrated output energies were 2.6 mJ for 304 nm and 2.3 mJ for
316 nm UV lines, with rooms to potentially achieve more energy for each laser. Linewidth narrowing was achieved using a volume Bragg grating as the output coupler of the OPO in each ring oscillator. We obtained spectral linewidths (FWHM) of 0.12 nm for the 304 nm line and 0.1 nm for the 316 nm line. Fibertek is now building an airborne DIAL transmitter based on the reported demonstration, which is a single optical module with dualwavelength output at the demonstrated wavelengths. NASA plans to field the DIAL transmitter as a key component of the Global Ozone Lidar
Demonstrator high altitude airborne instrument to perform autonomous global ozone DIAL remote sensing field campaigns.
9726-19, Session 4
Alexander Munk, Bernd Jungbluth, Michael Strotkamp,
Hans-Dieter Hoffmann, Reinhart Poprawe, Fraunhofer-
Institut für Lasertechnik (Germany); Josef Höffner, Leibniz-
Institut für Atmosphärenphysik e .V . (Germany)
In recent years scientific climate investigations have gained increasing importance. To validate numerical simulations of the Earth’s climate, temperature distributions in the atmosphere at altitudes between 80 and 110 km have to be investigated. Lidarsystems based on flashlamppumped Alexandrite ring lasers in single frequency operation represent
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a powerful source for these investigations but provide low efficiency and high maintenance effort. To overcome these drawbacks diode-pumped
Alexandrite lasers are required.
The 7 mm-long Alexandrite crystal was longitudinally pumped by a commercial diode bar module in the red spectral region and the resulting thermal lens was investigated at different operating points. A linear resonator was designed for operation in quasi-cw mode at 35 Hz and yielded to 4 mJ pulse burst energy at 770 nm with an optical efficiency of 21%. The wavelength could be tuned via temperature tuning of the
Alexandrite crystal. In Q-switched operation 0.8 mJ pulse energy were demonstrated at 770 nm and 35 Hz with a pulse duration of 300 ns.
Based on the results of the linear cavity a diode-pumped Alexandrite ring laser was realized. Two diode modules were used to longitudinally pump two Alexandrite crystals which were implemented in one oscillator. The ring laser was operated at 100 Hz in quasi-cw operation and 6.2 mJ pulse burst energy could be demonstrated at 770 nm. The resulting optical efficiency was 15%.
Further experiments should demonstrate Q-switched, unidirectional and single frequency operation of the Alexandrite ring laser. Power scaling can be carried out by subsequent amplification.
9726-20, Session 4
Conference 9726:
Solid State Lasers XXV: Technology and Devices
Anthony W . Yu, David J . Harding, Philip W . Dabney, NASA
Goddard Space Flight Ctr . (United States)
9726-21, Session 4
Philipp Kucirek, Ansgar Meissner, Patrick Eiselt, Marco
Höfer, Hans-Dieter Hoffmann, Fraunhofer-Institut für
Lasertechnik (Germany)
For measuring trace-gas abundances with the differential absorption lidar technique a pair of single-frequency laser pulses with highly stable emission wavelengths adjusted to the specific trace-gas of interest is required. In order to reduce mass and volume requirements for the laser beam source for a prospective space-borne system it is advantageous if the required pair of laser pulses is generated in only one optical assembly. For CO2 a detection wavelength of 2051 nm can be used, but the requirements on spectral stability are very challenging.
A q-switched Ho:YLF laser oscillator with a bow-tie ring resonator, specifically designed for high-spectral stability, is reported. It is pumped with gain-switched pulses from a Tm:YLF laser at 1.9 µ m. The ramp-and-fire method with a DFB-diode laser as a reference is employed for generating single-frequency emission. With a repetition rate of 50 Hz, pulse pairs with a temporal separation of 750 µ s are produced. The measured pulse energy is 2 mJ and the measured pulse duration is 15 ns for each of the two pulses in the burst. The standard deviation of the emission wavelength of the laser pulses of 2051 nm is measured with the heterodyne technique to be below
1.5 MHz over 2 seconds of integration time.
Future work will be in further increasing the spectral stability of the laser pulses and in building up an INNOSLAB pulse amplifier for pulse energy scaling towards 40 mJ (online pulse) and 15 mJ (offline pulse).
The Slope Imaging Multi-polarization Photon-counting Lidar (SIMPL) instrument is a polarimetric, two-color, multi-beam push broom laser altimeter developed through the NASA Earth Science Technology Office
Instrument Incubator Program and has been flown successfully on multiple airborne platforms since 2008. The SIMPL transmitter is based on a high repetition rate (~12 kHz), short-pulse (~1 ns), linearly-polarized microchip laser centered at 1064 nm. Part of the near infrared (NIR) beam at 1064 nm is frequency doubled to 532 nm (Green). Each of the NIR and Green beams is split into four push-broom beams. The output of the SIMPL instrument has 4 linearly-polarized beams each with co-aligned wavelengths in order to have co-incident NIR and Green footprints at the surface. A KTP crystal is used for the frequency doubling with temperature control used to vary conversion efficiency between 37% and 6% in order to equalize the signal strength of the two wavelengths as a function of surface type. A dichroic filter is used to separate the two colors into individual beam paths. In each of the beam paths, two tandem calcite crystals with different lengths and waveplates are used to separate the single input beam into four equally spaced beams. An array of half waveplates are used after the last calcite crystal to correct the alternating polarization of the four output beams so they have the same state of polarization (SOP). The NIR and Green beams are then recombined so they are co-aligned with the same SOP before entering a lens array for beam shaping and divergence control. A recent addition for this laser transmitter is a transmit echo pulse (TEP) feature for each color to quantify the pulse shape and amplitude for use in correcting received signal range biases. A receiver dichroic divides the two wavelengths into separate paths which are further divided using polarizing beam splitting cubes into signals parallel and perpendicular to the transmit beam. Sixteen single-photon counting modules (SPCM) and timing electronics with 0.1 nsec precision are used to determine range to the target for the four color/polarization states on the four beams. The short pulse width and high timing precision achieves an 8 cm range precision per single detected photon. Upon aggregation of the signal photons into a range histogram a measurement with a few cm resolution of pulse broadening is achieved. The broadening is due to surface slope and roughness within the footprint and light transmission into the target resulting in volume scattering. In this talk we will discuss the laser transmitter performance and present recent science data collected over the Greenland ice sheet and sea ice in support of the NASA Ice Cloud and land Elevation Satellite 2
(ICESat-2) mission to be launched in 2017.
9726-22, Session 4
Narasimha S . Prasad, NASA Langley Research Ctr . (United
States)
This paper discusses the recently completed post-flight test results of a
G-Stack diode laser unit that was sent on NASA’s MISSE 7 mission. The 5 bar G stack operating around 808 nm with 1 kW survived the harsh space environment with some reduction in performance due to contamination.
The objective of the Materials International Space Station Experiment
(MISSE) is to study the performance of novel materials when subjected to the synergistic effects of the harsh space environment for several months.
MISSE missions provided an opportunity for developing space qualifiable materials. This laser stack was a part of lidar component package on the
MISSE 7 box that was transported to the international space station (ISS) via STS 129 and returned to the Earth via STS 134. The STS 129 mission was launched on Nov 16, 2009 and the MISSE 7 package was brought back to the earth via the STS 134 that landed on June 1, 2011. This package that was in space environment for more than one and a half year included fiber laser, solid-state laser gain materials, coherent receiver, and semiconductor laser diode. The post-flight testing of several MISSE 7 materials that were recently returned back after more than one year of exposure on the International
Space Station (ISS) is underway. This paper will present the comparison of pre-flight and post-flight performance characteristics and discuss the effect of space exposure as well as contamination on the diode laser stack.
9726-53, Session 4
Jens Löhring, Michael Strotkamp, Florian Elsen, Raphael
Kasemann, Jürgen Klein, Martin Traub, Gerd Kochem,
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Conference 9726:
Solid State Lasers XXV: Technology and Devices
Ansgar Meisssner, Marco Höfer, Hans-Dieter Hoffmann,
Fraunhofer-Institut für Lasertechnik (Germany) discuss the overall design of the laser system, the current status, and further applications of this laser.
In the field of atmospheric research lidar is a powerful technology to measure remotely different parameters like gas or aerosol concentrations, wind speed or temperature profiles. For global coverage spaceborne systems are advantageous. To achieve highly accurate measurements over long distances high pulse energies are required.
A Nd:YAG-MOPA system consisting of a stable oscillator and two subsequent InnoSlab-based amplifier stages was designed and built as a breadboard demonstrator. Overall, more than 500 mJ of pulse energy at
100 Hz pulse repetition frequency at about 30 ns pulse duration in single longitudinal mode was demonstrated. Being seeded with 75 mJ pulses, the 2nd amplifier stage achieved an optical efficiency (pump energy to extracted energy) of more than 23% at excellent beam quality.
Recently, different MOPA systems comprising a single InnoSlab amplifier stage in the 100 mJ regime were designed and built for current and future airborne and spaceborne lidar missions. Amplification factors of about 10 at optical efficiencies of about 23% were achieved. In order to address the
500 mJ regime the established InnoSlab design was scaled geometrically in a straight forward way. Hereby, the basic design properties like stored energy densities, fluences and thermal load densities could be retained.
The InnoSlab concept has demonstrated the potential to fulfill the strong requirements of spaceborne instruments concerning high efficiency at low optical loads, excellent beam quality at low system complexity. Therefore, it was chosen as baseline concept for the MERLIN mission, currently in phase
B.
9726-24, Session 5
Axel Reiser, Juraj Bdzoch, Sven Höfer, Sina Riecke, Daniel
Seitz, Nicolas Kugler, Peter Genter, ROFIN-SINAR Laser
GmbH (Germany)
A novel laser system with optical parameters that fill the gap between
Q-switched and modelocked lasers has been developed.
It consists of a high gain hybrid fiber-bulk amplifier seeded by a low power
SESAM Q-switched oscillator. The mW level output power of the seed oscillator is preamplified by a single mode fiber which is limited by SRS effects. The final amplification stage is realized by two, longitudinal pumped,
Nd:YVO4 crystals in a double pass setup.
This MOPA configuration delivers sub-300ps pulses at repetition rates up to 1 MHz with an output power exceeding 60 Watt. Nonlinear frequency conversion to 532nm and 355nm is achieved with efficiencies of >75% and
>45%, respectively.
Due to the high peak power, high repetition rate and high beam quality of this system, applications formerly only addressable at lower pulse repetition frequencies or with complex modelocked laser systems are now possible with high speed and lower cost of ownership.
Application results that take benefit of these new laser parameters will be shown.
Furthermore, the reduction of the pulse duration to sub-100ps and power scaling to output powers >100 Watt by the use of the Innoslab concept are being presented.
9726-23, Session 5
Jason S . Zweiback, Logos Technologies, Inc . (United
States); Scott Fochs, Univ . of Rochester (United States);
Jake Bromage, Douglas Broege, Robert Cuffney,
Laboratory for Laser Energetics, University of Rochester
(United States); Zachary Currier, Logos Technologies Inc
(United States); Christopher Dorrer, Laboratory for Laser
Energetics, University of Rochester (United States); Brian
Ehrich, Univ . of Rochester (United States); Jim Engler,
Logos Technologies Inc (United States); Mark Guardalben,
Laboratory for Laser Energetics, University of Rochester
(United States); Nick Kephalos, Logos Technologies Inc
(United States); John Marozas, Richard Roides, Laboratory for Laser Energetics, University of Rochester (United
States); Jon Zuegel, Univ . of Rochester (United States)
A 100 J, 351 nm laser is under construction for the Dynamic Compression
Sector located at the Advanced Photon Source. This laser will drive shocks in solid-state materials which will be probed by picosecond x-ray pulses available from the synchrotron source. Using proven technology, the laser is designed for reliability and ease of use. A state-of-the-art fiber front end provides pulse lengths up to 20 ns with pulse shapes tailored to optimize shock trajectories. A diode-pumped Nd:glass regenerative amplifier is followed by a four-pass, flash-lamp-pumped rod amplifier. The regenerative amplifier is designed to produce up to 20 mJ with high stability. The final amplifier uses a six-pass 15-cm Nd:glass disk amplifier based on an OMEGA laser design. A KDP Type-II/Type-II frequency tripler configuration converts the 1053-nm laser output to a wavelength of 351 nm and the ultraviolet beam is image relayed to the target chamber. Smoothing by spectral dispersion and polarization smoothing have been optimized to produce uniform shocks in the materials to be tested. Modeling shows that better than 6% RMS uniformity should be achieved in a 500 mm diameter (FWHM) far-field spot. Custom control software collects all diagnostic information and provides a central control for all aspects of laser operation. We will
9726-25, Session 5
Julien Pouysegur, Florent Guichard, Institut d’Optique
Graduate School (France); Yoann Zaouter, Amplitude
Systèmes (France); Marc Hanna, Frédéric Druon, Institut d’Optique Graduate School (France); Clemens Hönninger,
Eric Mottay, Amplitude Systèmes (France); Patrick
Georges, Institut d’Optique Graduate School (France)
Work on a Fourier transform limited picosecond source composed of a seeder system tunable in pulse duration and a hybrid fiber – bulk amplifier able to provide large gain, high pulse energy, and high average power is presented. Spectral compression effect induced by self-phase modulation
(SPM) in an optical fiber is exploited to obtain the pulsewidth tunability.
To increase pulse energy beyond self-focusing threshold both in the fiber amplifier and Yb:YAG amplifier, Divided Pulse Amplification architecture is investigated. This had led to a source able to delivering 3ps 350 µ J pulses at 50 kHz of repetition rate, corresponding to an average power of 17.5W.
These performances are obtained in a compact and robust in a CPA free setup, and can be easily adjusted in a large range of pulsewidth (3 – 20 ps), energy (10 – 350 µ J), and average power (10 – 50 W), making it a particularly versatile source. A maximum pulse energy of 720 µ J has been demonstrated with 20ps pulse duration without any use of divided pulse scheme, corresponding to a peak power of 36MW per pulse. 116MW peak power has been made by reducing the pulse duration down to 3ps together with employment of divided pulse scheme generating 4 temporal replicas.
This hybrid configuration is well useful to improve by a factor of one hundred the output peak power of fiber systems available.
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9726-26, Session 5
Conference 9726:
Solid State Lasers XXV: Technology and Devices
Ryan Feeler, Chris Briggs, Wade Collins, Jay Doster,
Faming Xu, Northrop Grumman Cutting Edge Optronics
(United States)
A new generation of diode-pumped solid-state lasers has been developed that enables operation at high energies (1-10 J/pulse) and high repetition rates (tens to hundreds of Hz). Data for two separate lasers operating at
60Hz is presented – one a 1.2J, 532nm laser and the other a 1.5J, 1064nm, single longitudinal mode (SLM) laser. Data for a 10J, 1053nm, 20Hz, SLM system is also presented. The impact of wavelength seeding and oscillator design on the final output parameter of the laser is discussed.
A discussion of the suitability of these lasers in their applications (Raman spectroscopy, material inspection, and laser peening) is also discussed.
Special attention is paid to the design of the relay imaging system in these lasers, in order to generate the flat-top output beams that are required by these applications. Design details are presented and the path to higher pulse energies and repetition rates is discussed. Life test data for the pump diodes is also presented, demonstrating an expected operating lifetime in excess of
10 billion pulses before replacement diodes are required.
9726-27, Session 5
Bhabana Pati, Eric D . Park, Kenneth Stebbins, Q-Peak, Inc .
(United States)
Compact, lightweight, and efficient lasers are essential for space based and unmanned aerial vehicle (UAV) applications where there are constraints on size weight and power (SWaP). We have developed a compact, passively
Q-switched, intra-cavity frequency doubled Nd:YLF laser that produces
1-mJ of energy in a 10-ns pulse at a 1-30 Hz repetition rate. In order to obtain a high energy per pulse at repetition rates ~ 30 Hz, we chose Nd:YLF as the laser material as it has a longer upper state lifetime compared with the more common material, Nd:YAG. The laser is side-pumped by a semiconductor laser and passively Q-switched by a saturable absorber. A
KTP crystal is placed inside the laser resonator to double the laser frequency to generate green light at 523 nm. The resonator was optimized to obtain near diffraction limited beam. The overall volume of the laser head is < 8 cm3 and the weight is < 80 gm. The unique pumping geometry makes the laser power insensitive to the temperature over +/- 5 °C. The laser head is designed to be insensitive to mechanical or thermal misalignment.
Laser Science (Germany); Franz X . Kärtner, Deutsches
Elektronen-Synchrotron (Germany) and The Hamburg Ctr . for Ultrafast Imaging (Germany) and Ctr . for Free-Electron
Laser Science (Germany); Ingmar Hartl, Deutsches
Elektronen-Synchrotron (Germany); R . J . Dwayne Miller,
Max-Planck-Institut für Struktur und Dynamik der Materie
(Germany) and Ctr . for Free-Electron Laser Science
(Germany) and The Hamburg Ctr . for Ultrafast Imaging
(Germany)
We present, to the best of our knowledge, record high output pulse energies from Ho:YLF regenerative amplifier (RA) seeded by a Ho:Fiber oscillator.
The system delivers pulse energies of above 10 mJ at 100 Hz and above 4 mJ at 1 kHz, with less than 1.5 % rms fluctuation. The output spectrum of the pulses supports a Fourier limited duration of 2.8 ps. This laser system is ideally suited for ultrafast Mid-IR OPCPAs, high energy THz generation and strong-field experiments.
Due to the high energy storage capacity and long upper state life time of Ho:YLF, Ho:YLF RAs are highly susceptible to show pulse instability, in the form of bi- and multifurcation, when seeded with low energy seed pulses. We show both theoretically and experimentally that apart from a first operation region, a second operation point exists at a larger round trip number exhibiting almost one order of magnitude less pulse fluctuations.
This operation point is, to the best of our knowledge, demonstrated experimentally for the first time.
The experimental results are supported by simulations that reveal this system behavior under the conditions of a high gain build-up and high gain depletion for consecutive pump and amplification cycles. Here, the effects of seed and pump noise are negligible or significantly suppressed, respectively.
Operation at high pump powers and high pulse energies require a careful system design. We will also discuss general design guidelines for operation at the second stability point to suppress pulse instabilities without sacrificing high pulse energy.
9726-29, Session 6
Xavier Delen, Institut d’Optique Graduate School (France);
Loic Deyra, ALPhANOV (France) and Spark Lasers
(France); Simon Salort, ALPhANOV (France); Pascal
Dupriez, ALPhANOV (France) and Spark Lasers (France);
François Balembois, Patrick Georges, Institut d’Optique
Graduate School (France)
9726-28, Session 5
Peter Kroetz, Max-Planck-Institut für Struktur und
Dynamik der Materie (Germany) and Deutsches
Elektronen-Synchrotron (Germany); Axel Ruehl, Deutsches
Elektronen-Synchrotron (Germany); Anne-Laure
Calendron, Huseyin Cankaya, Deutsches Elektronen-
Synchrotron (Germany) and Ctr . for Free-Electron Laser
Science (Germany) and The Hamburg Ctr . for Ultrafast
Imaging (Germany); Krishna Murari, Deutsches Elektronen-
Synchrotron (Germany) and The Hamburg Ctr . for Ultrafast
Imaging (Germany) and Univ . Hamburg (Germany);
Gourab Chatterjee, Max-Planck-Institut für Struktur und
Dynamik der Materie (Germany) and Ctr . for Free-Electron
We demonstrate a high-gain, high-energy bulk amplifier in picosecond regime. The seed laser system is carefully optimized in order to obtained a central wavelength at 1064.3 nm and a spectral linewidth of 0.33 nm ideally matching the main emission line of Nd:YVO4. The fiber-based seed laser emits pulses with an energy of 5 nJ at repetition rates ranging from 1 kHz to 10 MHz and a pulse duration of 7 ps. The gain medium is a 20 mm long 0.2 at. % doped Nd:YVO4 crystal longitudinally pumped with a highbrightness, VBG locked 60 W fiber coupled laser diode emitting at 880 nm.
The amplifier is operated in a double pass configuration using a Faraday rotator to extract the signal beam after the second pass. Different pumping schemes are compared experimentally showing that two sides pumping results in higher output power than one side pumping. The output power of the amplifier ranges from 14.4 W to 25.5 W for seed powers between 20
µ W to 56 mW. For a repetition rate of 200 kHz, the output energy reaches up to 93 µ J with a pulse duration of 8 ps which gives a peak power of 11
MW. It corresponds to an output power of 18.6 W and a gain of 42 dB. The influence of the pumping scheme on the peak power limitation due to selfphase modulation is also studied. This source is well suited to meet specific requirements of micro-machining applications.
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Conference 9726:
Solid State Lasers XXV: Technology and Devices
9726-30, Session 6
Robert van Leeuwen, Bing Xu, Tong Chen, Qing Wang,
Jean-Francois Seurin, Princeton Optronics, Inc . (United
States); Guoyang Xu, Delai Zhou, Princeton Optronics Inc
(United States); Chuni L . Ghosh, Princeton Optronics, Inc .
(United States) stage Nd:YVO4 -amplifier up to the microjoule level ( up to >2 µ J pulse energy). We have demonstrated a simple laser system which generates
µ J-level, sub-10-ps pulses with a repetition rate tuneable from 0.2 to 1.4 MHz without active switching components and which can be integrated in a very compact setup.
9726-32, Session 6
Yuriy Stepanenko, Pawel Wnuk, Tomasz Kardas, Michal
Nejbauer, Czeslaw Radzewicz, Univ . of Warsaw (Poland)
Compact, low-cost, Q-switched diode-pumped solid-state lasers (DPPS) with high pulse energy are needed for many applications, such as laser range finders, laser designators, laser breakdown spectroscopy, and laser ignition. In many of those applications the lasers need to operate at high temperatures where typical edge-emitting laser diode pump lasers show poor reliability. Recently, high power vertical-cavity surface-emitting laser
(VCSEL) arrays have been demonstrated as excellent pump sources for diode-pumped solid-state lasers. Their key advantages over the existing edge-emitter technology include simpler coupling optics, reduced wavelength sensitivity to temperature, and increased reliability, especially at high temperatures, low-cost manufacturing, and two-dimensional planar scalability. These features make VCSEL technology very well suited for constructing low-cost DPSS lasers with high pulse energy.
Here we report on a very compact VCSEL end-pumped, passively
Q-switched Nd:YAG laser with high pulse energy. The laser only comprises 3 components: a high power VCSEL pump module, an aspheric condenser lens as a pump optic, and a diffusion bonded composite laser rod consisting of an Nd:YAG gain medium and a Cr:YAG saturable absorber. The laser rods are coated with high damage threshold dielectric coatings on each end to form the laser end mirrors. A thermal lens stabilizes the laser cavity. The laser pulse energy, q-switch delay time, and optical efficiency of the passively
Q-switched monolithic solid state lasers were measured as a function of
VCSEL power for various rod lengths, Cr doping levels, and VCSEL heatsink temperatures. Up to 23.6 mJ laser pulse energy was achieved with 11.9% optical efficiency.
Currently, there are two viable routes towards high peak-power laser systems. A traditional one relies on laser amplifiers in some variation of the
Chirped Pulse Amplification (CPA) scheme. Its major limitation comes from the thermal effects in the amplifying medium severely limiting the repetition rate laser systems. An alternative approach uses optical parametric amplification in a nonlinear crystal to transfer the energy directly from the pump beam to the amplified ultrashort pulse beam.
We will present the results on a table top multi-TW ns-pumped OPCPA system with time shear. The results of theoretical considerations show that, with proper design, the system can potentially achieve extremely high efficiency as well as good temporal and spatial characteristics of the pulses.
The possibility of usage of alternative, biaxial crystals (KTP, BiBO) with the pump and signal beams not necessary propagating within the major crystal planes will be discussed.
We will demonstrate experimental results of a system consisting of a femtosecond oscillator followed by a stretcher and a two-stage optical parametric amplifier. The amplifier is pumped with 532nm beam with a rectangular temporal pulse shape of 4 ns duration. The three-pass preamplifier boosts the nJ seed pulse energy by a factor of approximately
106. The power amplifier uses three BBO crystals enhancing the efficiency of the system to 35%. The spectrum of the output pulses is broad enough to support 15 fs pulse duration. This, together with hundreds of mJ of the output pulse energy shows that the system is capable of multi-TW operation.
9726-31, Session 6
Erdal Türkyilmaz, MONTFORT Laser GmbH (Austria);
Christian Guenther, Eva Mehner, Technische Hochschule
Nürnberg Georg Simon Ohm (Germany); Daniel Kopf,
MONTFORT Laser GmbH (Austria); Harald Giessen, Univ .
Stuttgart (Germany); Bernd Braun, Technische Hochschule
Nürnberg Georg Simon Ohm (Germany)
9726-33, Session 7
Raphael Clady, Vadim I . Tcheremiskine, Yasmina Azamoum,
Laurent Charmasson, Nicolas Sanner, Olivier P . Uteza,
Marc L . Sentis, Lasers, Plasmas et Procédés Photoniques
(France)
Commercial picosecond sources have found widespread applications.
Typical system parameters are pulse widths below 20 ps, repetition rates between 0.1 to 2 MHz, and micro Joule level pulse energies. Many systems are based on short pulse modelocked oscillators, regenerative amplifiers, and pockel cells as active beam switches. In contrast we present a completely passive system, consisting of a passively Q-switched microchip laser, a single-stage amplifier, and a pulse compressor. The Q-switched microchip laser has a 50 µ m long Nd:YVO4-gain material optically bonded to a thick undoped YVO4-crystal. It delivers pulse widths of 40 ps and repetition rates of 0.2 - 1.4 MHz at a wavelength of 1.064 µ m. The pulse energy is a few nJ. These 40-ps pulses are spectrally broadened in a standard single mode fiber and then compressed in a 24mm long CBG
(chirped Bragg grating) to as low as 3.3 ps. The repetition rate can be tuned from app. 0.2 to 1.4 MHz by changing the pump power while the pulse width and the pulse energy from the microchip laser are unchanged. The spectral broadening in the fiber is observed throughout the pulse repetition rate, supporting sub-10-ps pulses. Finally, the pulses are amplified in a single-
High intensity femtosecond laser are now routinely used to produce energetic particles and photons via interaction with solid targets. However, the relatively low conversion efficiency of such processes requires the use of high repetition rate laser to increase the average power of the laser-induced secondary source. Furthermore, for high intensity laser-matter interaction, a high temporal contrast is of primary importance as the presence of an ASE
(Amplified Spontaneous Emission) pedestal and/or various prepulses may significantly affect the governing interaction processes by creating a preplasma on the target surface.
We present the characterization of a laser chain based on Ti:Sa technology and CPA technique, which presents unique laser characteristics in the world: a high repetition rate (100 Hz), a high peak power (10 TW) and a high contrast ratio (ASE <10-10, prepulses <10-8) obtained thanks to a specific design with 2 saturable absorbers inserted in the amplification chain. A deformable mirror placed before the focusing parabolic mirror allows focusing the beam almost at the limit of diffraction. In these conditions,
10 SPIE Photonics West 2016 · www.spie.org/pw
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we obtained peak intensity above 1019W.cm-2 on target, which allows the study of phenomena in the relativistic optic domain at an unprecedented repetition rate. Preliminary results on the generation of a sub-picosecond laser-driven hard x-ray Kalpha source with a 100 Hz repetition rate are also presented, with a particular emphasis on the influence of the different laser parameters.
9726-34, Session 7
Conference 9726:
Solid State Lasers XXV: Technology and Devices
Andreas Rohrbacher, Vesna Markovic, Wolfgang
Pallmann, Simonette Pierrot, Peter Hofmann, Lumentum
(Switzerland); Bojan Resan, Lumentum (Switzerland) and Univ . of Applied Sciences and Arts Northwestern
(Switzerland)
Ti:sapphire oscillators are the proven technology to generate sub-100 fs
(even sub-10 fs) pulses in the near infrared and are widely used in many high impact scientific fields. However, the need for a bulky, expensive and complex pump source, typically a frequency-doubled multi-watt solid-state laser, represents the main obstacle to more widespread use. The recent development of blue diodes emitting over 1 W has opened up the possibility of directly diode-laser-pumped Ti:sapphire oscillators. Beside much lower cost and smaller footprint, direct diode pumping provides better reliability, higher efficiency and better pointing stability. The associated challenges are lower absorption of Ti: sapphire at available diode wavelengths and lower brightness of blue diodes compared to typical solid-state green pump lasers.
For applications such as biomedical imaging and nano-structuring, output powers in excess of 100 mW and sub-100 fs pulses are required. In this paper, we demonstrate a high pulse energy directly blue-diode-pumped
Ti:sapphire oscillator without watercooling. The SESAM modelocking ensures reliable self-starting and robust operation. We will present two configurations emitting 460 mW average power with 88 fs pulses and
350 mW average power with 75 fs pulses, both operating at 92 MHz pulse repetition rate. The maximum obtained pulse energy reaches 5 nJ. A doublesided pumping scheme with two high power blue diode lasers, emitting 2.9
W each, was used for the output power scaling. The cavity design and the experimental results will be discussed in more details.
4-mm long and 1.5% doped. The low-power oscillator was pumped by two single-mode fiber-coupled laser diodes, emitting 400 mW maximum power at 976 nm. Up to 65 mW average output power, 78-fs long modelocked pulses with 18 nm FWHM spectral bandwidth centered at 1075 nm were obtained in a resonator employing a single prism for intracavity GDD compensation. In high-power amplification experiments, we pumped two
Yb:Lu2O3 crystals, each with a 60-W fiber-coupled laser diode. The seeder was a Yb:KYW oscillator delivering 250-fs long, almost Fourier transform limited pulses at 1035 nm. Before injection in the regenerative amplifier, pulses were stretched to about 30-ps. Average output powers up to 27.8
W at 500 kHz were achieved before compression and at maximum pump power. Pulse energies up to 44.4 µ J and pulse durations of 638 fs were demonstrated after a standard grating compressor. The 2.8-nm FWHM wide spectrum was centered at 1034 nm, resulting in a time-bandwidth product of 0.5. We measured a M2<1.3 in both axes at full pump power.
9726-36, Session 7
Christoph Pflaum, Friedrich-Alexander-Univ . Erlangen-
Nürnberg (Germany); Rainer Hartmann, Friedrich-
Alexander-Univ . Erlangen-Nürnberg (Germany) and
Erlangen Graduate School in Advanced Optical
Technologies (Germany); Zhabiz Rahimi, ASLD GmbH
(Germany)
Ultrashort pulses with high average power are required for a variety of technical and medical applications. To increase the power of ultrashort lasers, single, multi-pass, and regenerative amplifiers are used. Typical laser crystals for such amplifiers include the Ti:Sapphire or Yb:YAG laser crystals.
Difficulties in the amplification of ultrashort pulses include gain narrowing effects and dispersion effects in the laser crystal. In particular these complications arise, when a pulse stretcher is needed before amplification of the laser beam.
We present a technique to model and simulate the amplification of ultrashort pulses. This technique allows to model both gain narrowing effects and decrease of beam quality caused by amplification of the laser beam. This requires a detailed 3-dimensional simulation of population inversion. Gain narrowing effects are taken into account by analyzing the gain of the spectrum of the laser beam. Important is to distinguish amplifiers with one or only two passes and a regenerative amplifier. These two different kind of amplifiers are modeled by different approaches. A regenerative amplifier is modeled by a set of time dependent rate equations.
However, a single pass amplifier is modeled by a set of spatial dependent rate equations. In both cases, a system of rate equations arises from spectral discretization of the laser beam. Detailed simulation results are presented.
9726-35, Session 7
Etienne Caracciolo, Univ . degli Studi di Pavia (Italy) and
Spectra-Physics (Austria); Federico Pirzio, Univ . degli
Studi di Pavia (Italy); Matthias Kemnitzer, Spectra-Physics
(Austria); Annalisa Guandalini, Spectra-Physics (Austria);
Florian Kienle, Spectra-Physics (Austria); Antonio Agnesi,
Univ . degli Studi di Pavia (Italy); Juerg Aus der Au,
Spectra-Physics (Austria)
9726-37, Session 7
Olivier J . Chalus, Alain Pellegrina, Olivier Casagrande,
Christophe Derycke, Laurent Boudjemaa, Christophe
Simon-Boisson, Sébastien Laux, François Lureau, Thales
Optronique S .A .S . (France)
Yb:Lu2O3 is a very promising material for high-power ultrashort pulse generation and amplification owing to a favorable combination of good thermo-mechanical properties, comparable to those of Yb:YAG, and a relatively broad emission bandwidth, able to sustain sub 100-fs pulses.
Here we report, to the best of our knowledge, the shortest pulse duration ever demonstrated in a Yb:Lu2O3 oscillator and the highest average power from a bulk Yb:Lu2O3 regenerative amplifier. Both for low-power oscillator and regenerative amplification experiments, the Yb:Lu2O3 samples were
In the frame work of the ELI-NP project, we have developed a broadband high contrast (>1:1014) 10mJ seeder for 2 x 10PW laser. This hybrid
Ti:Sapphire/OPCPA Front End is usable for any ultra-short pulse PetaWatt laser system, or above. It consists of an oscillator developed in collaboration with Venteon GmbH providing the seed for the system as well as an optically synchronized seed for the OPCPA pump. The 800nm seed is first amplified in a regenerative amplifier and is then compressed. This
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Conference 9726:
Solid State Lasers XXV: Technology and Devices compressed pulse is injected in a XPW filter allowing enhancement of the contrast of four orders of magnitude. This pulse is then stretched in bulk to a few tens of picosecond and amplified in a double stage OPCPA at 10Hz.
A gain of 3orders of magnitude in the OPCPA also allows a contrast gain of equivalent amount at 100ps. The OPCPA design is compatible with pump lasers working at 1064nm using the mature and reliable technology of flashlamp pumped Nd:YAG, allowing future scaling to higher energies and with pulse duration of twenty five picoseconds. A record optical efficiency of the OPCPA of 20% has been reached without any spatial and temporal shaping device within the pump laser. The total bandwidth at the output of the frontend exceeds 120nm therefore allowing ultrashort pulse after compression. R.M.S stability better than 1.5% over more than one hour has been demonstrated.
9726-38, Session 7
Florian Harth, Melissa C . Piontek, Thomas Herrmann,
Johannes L’huillier, Photonik-Zentrum Kaiserslautern e .V .
(Germany) beamline of HPLS (High Power Laser System) built by Thales for ELI NP.
Each beamline is seeded by a common front end combining Titanium
Sapphire CPA and BBO based OPCPA stage in order to improve the temporal contrast and to enlarge the spectral bandwidth. The OPCPA output is split into 2 beams which are launched into beamlines based on amplification within Ti:Sa crystals including spectral filters to compensate for gain narrowing and spectral shifting effects. Each beamline will provide a main 10 PW output at the rate of 1 shot per minute and two compressed intermediate outputs of respectively 100 TW at 10 Hz and 1 PW at 1 Hz.
The front end has been entirely built and the OPCPA stage has been able to deliver 10.5 mJ for a 532 nm pump energy of 55 mJ. On the first beamline,
2 of the 3 amplification sections have been built and characterized. At the
PW intermediate output, an energy per pulse of 39 J before compression has been demonstrated and the related spectral bandwidth is 75 nm FWHM, suggesting future compression below 20 fs. In addition to this, 5 of the 8 pump modules of the final amplifier have been already built. Each module based on flashlamp-pumped Nd-doped Phosphate Glass delivers after second harmonic generation in a LBO crystal more than 100 J of green light at 527 nm while the energy stability is better than 0.6% rms
9726-40, Session 8
Knut Michel, Sandro Klingebiel, Marcel Schultze, Catherine
Y . Tesseit, Christoph Wandt, Stefan Prinz, Robert Bessing,
Matthias Häfner, Thomas Metzger, TRUMPF Scientific Laser
GmbH + Co ., KG (Germany); Dirk Sutter, TRUMPF Laser
GmbH (Germany)
A new generation of resonant scanners in the kHz-range shows ultra high deflection speeds of more than 1000 m/s but suffer from an inherent nonlinear mirror oscillation. A typical bitmap, written point by point, would be strongly distorted because of the decreasing spot distance at the turning point of the scanning mirror. Furthermore, laser micromachining with constant pulse repetition frequency (PRF) even in narrow vector geometries can cause severe heat accumulation with resulting degradation of the machining quality. This can be avoided by a dynamic adaption of the PRF of the ultrafast laser. However, in the case of the resonant scanner this means that the PRF has to be continuously swept up to several 10.000 times per second between e.g. 5 MHz and 10 MHz. Even today this is still a challenging task.
We present a laser system which is capable of sweeping the PRF more than 32.000 times per second between 5 MHz and 10 MHz at an average output power of up to 120 W at 515 nm with a pulse duration of about 40 ps. The laser consists of a semiconductor oscillator, a 3-stage fiber preamplifier, a solid state power amplifier (AMPHOS 200) and a SHG stage.
We systematically analyzed the dynamic of the laser system as well as the spectral and temporal behavior of the optical pulses. Switching the repetition rate typically causes a varying pulse energy, which could affect the machining quality over one scanning line. This effect will be analyzed and discussed. Possible techniques to compensate or avoid this effect will be considered.
9726-39, Session 7
François Lureau, Sébastien Laux, Olivier Casagrande,
Olivier Chalus, Pierre-Antoine Duvochelle, Sandrine
Herriot, Guillaume Matras, Christophe Radier, Christophe
Simon-Boisson, Thales Optronique S .A .S . (France);
Alexandru Boianu, Horia Hulubei National Institute of
Physics and Nuclear Engineering (Romania); Ioan Dancus,
Razvan Dabu, National Institute for Laser, Plasma and
Radiation Physics (Romania)
We report on the latest developments at TRUMPF Scientific Lasers in the field of ultra-short pulse lasers with highest output energies and powers. All systems are based on the mature and industrialized thin-disk technology of TRUMPF. Thin Yb-YAG disks provide a reliable and efficient solution for power and energy scaling to Joule- and kW-class picosecond laser systems.
Due to its efficient one dimensional heat removal, the thin-disk exhibits low distortions and lensing even when pumped under extremely high pump densities of 10kW/cm?. Currently TRUMPF Scientific Lasers develops regenerative amplifiers with highest average powers, optical parametric amplifiers and synchronization schemes. The first few-ps kHz multi-mJ thin-disk regenerative amplifier based on the TRUMPF thin-disk technology was developed at the LMU Munich in 2007. Since, the average power and energy have continuously been increased, reaching more than 300W (10kHz repetition rate) and 200mJ (1kHz repetition rate) at pulse durations below
2ps. First experiments have shown that the current thin-disk technology supports ultra-short pulse laser solutions >1kW of average power.
Based on few-picosecond thin-disk regenerative amplifiers few-cycle optical parametric chirped pulse amplifiers (OPCPA) can be realized. These systems have proven to be the only method for scaling few-cycle pulses to the multi-mJ energy level. OPA based few-cycle systems will allow for many applications such as attosecond spectroscopy, laser wake field acceleration, table-top few-fs accelerators and laser-driven coherent X-ray undulator sources.
Furthermore, high-energy picosecond sources can directly be used for a variety of applications such as X-ray generation or in atmospheric research.
9726-41, Session 8
(Invited Paper)
Sven-Silvius Schad, Tina Gottwald, Vincent Kuhn, Matthias
Ackermann, Dominik Bauer, Michael Scharun, Alexander
Killi, TRUMPF Laser GmbH (Germany)
We present the latest results obtained on the first 10 PetaWatt laser
12 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9726:
Solid State Lasers XXV: Technology and Devices
The disk laser is one of the most important laser concepts for today’s industrial market. Offering high brilliance at low cost, high optical efficiency and great application flexibility the disk laser paved the way to many industrial laser applications. Over the past years power and brightness increased and the disk laser turned out to be a very versatile laser source, not only for welding but also for cutting. Both, the quality of the cut and speed are superior to previous CO2-based lasers for a vast majority of metals, and, most important, through a broad thickness range. In addition, the insensitivity against back reflections makes the disk laser suited for cutting highly reflective metal such as brass or copper. These advantages entail versatile cutting machines and explain the high and growing demand for disk lasers besides the classic welding application as can be observed today.
For the time being, the disk principle has not reached any fundamental limits regarding output power per disk or beam quality, and offers numerous advantages over other high power resonator concepts, especially over fiber lasers or even direct diode lasers. This paper will give insight in the latest progress in kW-disk laser technology at TRUMPF and will discuss recent results as well as power scaling strategies.
For many industrial and scientific applications, stable picosecond pulse laser operation at high repetition rate from 1kHz to 100kHz with good spatial beam quality is essential. Development of such kW-class Yb:YAG thin disk beamlines is going to be finished in 2015 at the Hilase facility.
A compact high repetition rate (100kHz) zero-phonon-line-pumped regenerative amplifier (footprint only 120x80cm incl. a pulse compressor) is reliably operated with 1mJ pulse energy in fundamental spatial mode.
Output pulse was successfully compressed bellow 2 ps by a tiny CVBG compressor and converted to second and fourth harmonic with >65% and
18% conversion efficiency, respectively. Upgrade of the regen to 5mJ will be demonstrated soon. The cavity of the upgrade amplifier has already been tested in CW regime with 560W output power and no sign of roll over.
Results of the seeded operation, efficiency of pulse compression at 0.5kW by a CVBG, and results of improved conversion to 2nd and 4th harmonics will be presented.
Other beamline which is being developed is a double stage 1kHz beamline with 0.5J expected energy in a picosecond pulse. The first stage, a
QCW-pumped Yb:YAG regenerative amplifier, is now used in application experiments with 45mJ pulse energy after compression by a grating-based compressor. Pulse length is <3ps and beam quality M2 =1.25. The second stage, a regenerative amplifier with a ring cavity, is being assembled now.
Until end of 2015 we expect operation with multi-100mJ pulse energy. An overview and the latest results of all thin-disk beamlines will be presented.
9726-42, Session 8
Thomas Sartorius, Peter Rußbüldt, Fraunhofer-Institut für Lasertechnik (Germany); Dominik Bauer, Dirk Sutter,
TRUMPF Laser GmbH (Germany); Hans-Dieter Hoffmann,
Fraunhofer-Institut für Lasertechnik (Germany)
9726-44, Session 8
John Vetrovec, Drew A . Copeland, Amardeep S . Litt,
Aqwest, LLC (United States); Detao Du, General Atomics
Aeronautical Systems, Inc . (United States) We present an Ytterbium based amplifier system for fs-pulses that combines the high gain of Innoslab amplifiers and the high average power of disk amplifiers. The system delivers an average power of 1.5 kW at a repetition rate of 40 MHz. The energy of the pulses results in 37.5 µ J. The pulse duration was measured to be 710 fs. The beam quality is M? = 1.5 x 2.0.
The seed source of the amplifier system is a commercial fiber MOPA with 7
W average power. The power is increased by a two-stage Innoslab amplifier to 720 W. After spatial filtering a beam quality of M? = 1.24 x 1.14 is achieved at an average power of 630 W.
The last stage of the amplifier system is a thin-disk multipass amplifier. The
Yb:YAG disk module is pumped with 4.2 kW at a pump spot diameter of approximately 10 mm. The laser beam is folded 18 times over the disk within a total beam path of 22 m using flat mirrors and three lenses with a focal length f = -8 m to compensate the focal power of the disk at 4.2 kW pump power. The total gain is currently limited by the number of reflections off the disk, and by thermal issues in the multi-pass arrangement. An improvement of the output beam quality should be possible via better mode matching to the pumped spot on the disk.
We report on a Yb:YAG laser amplifier for ultrashort pulse applications at kW-class average power. The laser uses two large aperture, disk-type gain elements fabricated from composite ceramic YAG material, and a multipassing architecture to obtain high gain in a chirped-pulse amplification system. The disks are edge-pumped [1, 2, 3], thus allowing for reduced doping of crystals with laser ions, which translates to lower lasing threshold and lower heat dissipation in the Yb:YAG material. The latter makes it possible to amplify a near diffraction-limited seed without significant thermo-optical distortions.
This work presents results of testing the laser amplifier with relay optics configured for energy extraction with up to 40 passes through the disks.
This work was in-part supported by the US Army ARDEC Contract Number
W15QKN09C0156. Applications for the ultrashort pulse laser amplifier include laser induced plasma channel, laser material ablation, and laser acceleration of atomic particles.
1. J. Vetrovec et al., “Ytterbium–based disk amplifier for an ultra–short pulse laser,” SPIE vol. 7578 (2010).
2. J. Vetrovec et al., “Initial Testing of Edge-Pumped Yb:YAG Disk Laser with
Multi-Passed Extraction,” SPIE vol. 8235 (2012).
3. J. Vetrovec et al., “Erbium-Based Edge-Pumped Disk Laser,” SPIE vol.
8599 (2013).
9726-43, Session 8
Martin Smr?, Taisuke Miura, HiLASE Ctr . (Czech Republic);
Michal Chyla, Jiri Muzik, Siva S . Nagisetty, HiLASE Ctr .
(Czech Republic) and Czech Technical Univ . in Prague
(Czech Republic); Ondrej Novák, Hana Turcicova, Jens
Linnemann, HiLASE Ctr . (Czech Republic); Jaroslav Huynh,
Patricie Severová, Pawel Sikocinski, HiLASE Ctr . (Czech
Republic) and Czech Technical Univ . in Prague (Czech
Republic); Akira Endo, Tomá? Mocek, HiLASE Ctr . (Czech
Republic)
9726-45, Session 8
John Vetrovec, Drew A . Copeland, Amardeep S . Litt,
Aqwest, LLC (United States)
We report on a new class of laser amplifiers for inertial confinement fusion (ICF) drivers based on a Yb:YAG ceramic disk in an edge-pumped configuration cooled by a high-velocity gas flow. The Yb lasant offers
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Conference 9726:
Solid State Lasers XXV: Technology and Devices very high efficiency and low waste heat. The ceramic host material has a thermal conductivity nearly 15-times higher than glass and it is producible in sizes suitable for a typical 10 to 20 kJ driver beam line. The combination of high lasant efficiency, low waste heat, edge-pumping, and host thermal conductivity, enable operation at 10 to 20 Hz at over 20% wall plug efficiency.
This work shows that the edge-pumped Yb:YAG driver operating at ambient temperature offers superior wall-plug efficiency with comparably smaller and less costly pump diodes than recently considered facepumped alternative drivers using Nd;glass, Yb:S-FAP, and cryogenic Yb:YAG gain elements [1].
Scalability of the laser driver over a broad range of sizes is presented. Also included is a design of a subscale 400-J laser amplifier in a configuration directly scalable to a full-size driver. When equipped with Yb:sesquioxide ceramic gain elements for improved bandwidth, the 400-J amplifier can be used in a driver for laser acceleration of nuclear particles. This work was in-part supported by the US Department of Energy Grant Number DE-
SC0011916.
1. A.C. Erlandson, et al., “Comparison of Nd:phosphate glass, Yb:YAG, and
Yb:S-FAP laser beamlines for laser inertial fusion energy (LIFE), Optical materials Express, vol. 1, no. 7, November 1, 2011.
9726-9, Session PTue
Helena Jelínková, Czech Technical Univ . in Prague (Czech
Republic); Maxim E . Doroshenko, A . M . Prokhorov General
Physics Institute (Russian Federation); Jan ?ulc, Michal
N?mec, Michal Jelínek, Czech Technical Univ . in Prague
(Czech Republic); Vjatcheslav V . Osiko, A . M . Prokhorov
General Physics Institute (Russian Federation); Valerii V .
Badikov, Dmitri V . Badikov, Kuban State Technological
Univ . (Russian Federation)
9726-68, Session PTue
Michal N?mec, Lukás Indra, Jan ?ulc, Helena Jelínková,
Czech Technical Univ . in Prague (Czech Republic)
Laser sources generating radiation in the spectral range from 1.5 to 1.7 um are very attractive for many applications such as satellite communication, range finding, spectroscopy, and atmospheric sensing. The goal of our research was an investigation of continuous-wave generation and wavelength tuning possibility of diode pumped eye-safe Er:YAG laser emitting radiation around 1645 nm. We used two 0.5 at. % doped Er:YAG active media with lengths of 10 mm and 25 mm (diameter 5 mm). As a pumping source, a fibre-coupled 1452 nm laser-diode was utilized, which giving possibility of the in-band pumping with small quantum defect and low thermal stress of the active bulk laser material.
The 150 mm long resonator was formed by the pumping mirror (HT @ 1450 nm, HR @ 1610 - 1660 nm) and output coupler with 96 % reflectivity at 1610 -
1660 nm. For continuous-wave generation, the maximal output powers were
1 W and 0.7 W for 10 mm and 25 mm long laser crystals, respectively. The corresponding slope efficiencies with respect to absorbed pump power for these Er:YAG lasers were 26.5 % and 37.8 %, respectively. The beam spatial structure was close to the fundamental Gaussian mode. The wavelength tunability was realized by a birefringent plate and four local spectral maxima at 1616, 1632, 1645, and 1656 nm were reached.
The output characteristics of the designed and realized resonantly diodepumped eye-safe Er:YAG laser show that this compact system has a potential for usage mainly in spectroscopic fields.
9726-69, Session PTue
Richard ?vejkar, Jan ?ulc, Michal N?mec, Helena Jelínková,
Czech Technical Univ . in Prague (Czech Republic); Maxim
E . Doroshenko, Pavel P . Fedorov, Vjatcheslav V . Osiko, A . M .
Prokhorov General Physics Institute (Russian Federation)
On the basis of our previous Dy3+:PbGa2S4 laser study, the laser output wavelength temporal evolution as well as tuning possibilities in the range
4.3–4.7um were investigated. Active crystal 12x6x2mm3 was pumped by a fiber-coupled Brightlase Ultra-50 diode laser (1.7um, max. power 7.5W).
The laser resonator was formed by a flat dichroic pumping mirror (T =
70%@1.7um, R~100%@3.5 - 5um) and a concave (r = 200mm) output coupler with R~99%@3.5 - 5um. In order to decrease thermal loading to the active crystal, the laser was operated in the pulsed regime at 10 Hz with various pump pulse duration. The laser output wavelength dependence on the pump pulse duration and its evolution within the pump pulse was investigated at first without any spectrally-selective filter in the resonator. At pump pulse duration of 1ms, generation just at 4.35um has been observed.
Prolongation to 5ms led to generation at 4.35um in the first millisecond, followed by simultaneous generation at 4.35 and 4.38um in the second millisecond, and further followed by generation almost just at 4.6um till the end of the pump pulse. Prolongation to 10ms led to similar behavior as in the previous case followed by generation at 4.6um only. Furthermore, output wavelength tuning possibilities using MgF2 birefringent filter inside the resonator were investigated under 10ms pumping. Almost continuous tuning without any significant dip has been observed in the wavelength range 4.3 up to 4.7um. The mean output power was in the order of 400uW corresponding to the power amplitude of 4mW.
We present laser and spectroscopic properties of crystal Er,La:SrF2-CaF2 at temperature range 80 - 320 K, which is appropriate for generation of radiation around 2.7 _m. The sample of Er,La:SrF2-CaF2 (concentration
Er(0.04), La(0.12):Ca(0.77)Sr(0.07)) had plan-parallel face-polished faces without anti-reflection coatings (thickness 8.2 mm). During spectroscopy and laser experiments the Er,La:SrF2-CaF2 was attached to temperature controlled copper holder and it was placed in vacuum chamber. The transmission and emission spectra of Er,La:SrF2-CaF2 together with the fluorescence decay time were measured in dependence on temperature.
The excitation of Er,La:SrF2-CaF2 was carried out by a laser diode radiation
(pulse duration 5 ms, repetition rate 20 Hz, pump wavelength 973 nm).
Laser resonator was hemispherical, 140 mm in length with flat pumping mirror (HR @ 2.7 um) and spherical output coupler (r = 150 mm, R = 95
% @ 2.5 - 2.8 um). Tunability of laser at 80 K in range 2690 - 2765 nm was obtained using MgF2 birefringent filter. With decreasing temperature of sample the fluorescence lifetime of manifold 4I11/2 (upper laser level) became shorter and intensity of upconversion radiation was increasing. The highest slope efficiency with respect to absorbed power was 2.3 % at 80 K.
The maximum output of peak amplitude power was 0.3 W at 80 K, i.e. 1.5 times higher than at 300 K. The wavelength generated by Er,La:SrF2-CaF2 laser (2.7 um) is relatively close to absorption peak of water (3 um) and so, one of the possible use should be in medicine.
14 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9726:
Solid State Lasers XXV: Technology and Devices
9726-70, Session PTue
Xiao Yuan, Han Xiong, Fan Gao, Xiang Zhang, Soochow
Univ . (China)
9726-72, Session PTue
Karel Veselsk?, Jan ?ulc, Helena Jelínková, Czech Technical
Univ . in Prague (Czech Republic); Karel Nejezchleb, Václav
?koda, CRYTUR spol s .r .o . (Czech Republic)
Laser beams will inevitably encounter modulations of spatial frequencies when propagating in optical paths, resulting in small-scale self-focusing and degrading the beam quality, especially in inertial confinement fusion lasers that have higher intensities. Spatial filter (SF) is an effective equipment to clean off the rapidly growing spatial frequencies, which consists of two convex lenses and a pinhole placed at their common focus. Nonetheless, the pinhole aperture should be less than a specific size to efficiently clean off the rapidly growing spatial frequencies, thus the pinhole aperture in large laser systems has to bear higher intense laser irradiation, which may induce pinhole closure. Besides, the SFs in large laser systems have to be placed in high vacuum to avoid breakdown in air. In order to solve the above problems, the conventional pinhole SF has to be improved. By introducing cylindrical lenses into SFs, the laser beams can be focused into a line instead of the original spot, thus the focal area can be significantly enlarged and the focal intensity greatly lowered.
We propose a new-type two-lens slit SF with two complex cylindrical lenses and two crossed slits. The characteristics of this slit filter on image relay, aperture match and spatial filtering are discussed by both theoretical calculations and numerical simulation. In simulation, we use this new-type
SF to replace the original transmission spatial filter (TSF) in NIF system, and found that the focal intensity on the slit drops by about 3 orders of magnitude, which greatly improves the pinhole closure for large laser systems and could reduce the vacuum degree in SF by about one order of magnitude, which is helpful in building and maintaining the large laser systems.
The aim of this study was to investigate whether refractive power of thermal lens for Yb:LuAG crystal at cryogenic temperatures depends on Yb doping concentration which has not been examined yet. The three measured
Yb:LuAG laser rods samples (length of 3 mm, diameter 3 mm, AR @ 0.94
µ m and 1.03 µ m, doping concentration 5.4, 8.4 and 16.6 at. % Yb/Lu) were mounted in the temperature controlled copper holder of the liquid nitrogen cryostat. Samples were longitudinally pumped with fiber coupled CW laser diode at 0.930 µ m with the focal point 0.2 mm in diameter. The 38 mm long semi-hemispherical laser resonator consisted of a flat pump mirror
(HR @ 1.03 µ m and HT 0.94 µ m) and curved output coupler (r=500 mm) of reflectivity 94 % @ 1.06 µ m. The refractive power of thermal lens was estimated indirectly by measuring of change in the position of focused laser beam focal point. The measurement was performed for constant absorbed power of 10 W in temperature range from 80 up to 240 K. It was observed that cryogenic cooling caused reduction of thermal lens power, which increased linearly with increasing temperature and was the same for each sample of different dopant concentration. Presented study shows that application of cryogenic temperature leads to reduction of thermal effect even for high dopant concentration in Yb:LuAG crystal. This is essential for reaching of high output power while maintaining high beam quality.
9726-71, Session PTue
Martin Fibrich, Jan ?ulc, Helena Jelínková, Czech Technical
Univ . in Prague (Czech Republic)
9726-73, Session PTue
Petr Navratil, Venkatesan Jambunathan, Lucie Horackova,
Antonio Lucianetti, Tomas Mocek, Institute of Physics of the ASCR, v .v .i . (Czech Republic)
In this contribution, 1 W of the output power in the orange spectral range
(607 nm) under blue laser diode pumping of the Pr:YLF crystal is reported.
To reduce reabsorption losses at this particular 3P0 ? 3H6 laser transition
(originating from the higher laying level of the ground state manifold to the
1D2 manifold), the laser system was designed for operation at cryogenic temperature.
In our experiment, 0.4 at. % doped 4 mm long non-antireflection coated
Pr:YLF crystal mounted on a liquid-nitrogen-cooled copper finger in the vacuum chamber of the cryostat was employed. Temperature of the sample was kept at 80 K. As a pump source, a fiber-coupled (core diameter 400 um, NA 0.22) blue laser diode module from Necsel company was used. The module provided 442 nm laser radiation with maximal output power of 10
W which was collimated and subsequently focused into the laser crystal by two antireflection coated achromatic doublets having focal lengths of
75 mm both. Pump absorption efficiency of the crystal was measured to be only 31 %, due to the non-perfect overlapping of the diode emission spectrum and the 444 nm absorption peak of the Pr:YLF crystal. Using 70% output coupler reflectivity at the designed laser wavelength, more than 1 W of the output power at 607 nm was reached from the Pr:YLF sample. The corresponding slope efficiency related to absorbed pump power was 37 %.
To our best knowledge, this is the first demonstration of diode pumped 1-W class Pr-ion based orange emitting laser system.
Development of compact diode pumped passive Q-switched solid state lasers with high peak power has become scientific interest because of their vast technological applications such as laser ignition, material processing, nonlinear optical studies, optical communications, etc. Especially for industrial applications compact, low maintenance, robust, stable and alignment free pulsed lasers are inevitable.
In this aspect, we are developing compact pulsed laser based on Yb:YAG/
Cr:YAG. It consists of monolithic crystal having cylinder shape with 5mm in diameter that houses both the active medium Yb:YAG (3at.% Yb/Y,
3mm length) and Cr:YAG saturable absorber (initial transmission 90%,
1mm length) which are diffusion bonded. The laser resonator is formed by depositing the dielectric mirrors on the surface with Yb-doped segment having high reflection for laser wavelength and high transmission for pump wavelength, while the reflection of laser wavelength on the Cr-doped side is
80%, meaning that 20% of generated light is extracted. The laser is pumped longitudinally by fiber coupled VBG stabilized laser diode emitting at 969nm and the monolithic crystal is cooled down to cryogenic temperatures.
In the initial experiment for temperature 140K we attained stable pulse operation with pulse energy over 60 µ J and pulse width of 1ns which leads to a peak output power better than 60kW.
Present work is focused on optimizing the thickness, doping and transmission of output coupling to extract more energy. Both the experimental results and theoretical modelling based on this compact cryogenic laser will be presented in detail.
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+1 360 676 3290 · help@spie.org 15

9726-74, Session PTue
Karel Nejezchleb, CRYTUR spol s .r .o . (Czech Republic);
Jan ?ulc, Helena Jelínková, Czech Technical Univ . in Prague
(Czech Republic); Václav ?koda, CRYTUR spol s .r .o . (Czech
Republic)
V:YAG crystal was investigated as a passive Q-switch of longitudinally diode-pumped microchip laser, emitting radiation at wavelength 1030.5 nm. This laser was based on diffusion bonded monolith crystal (diameter 3 mm) which combines in one piece an active laser part (Yb:YAG crystal, 10 at.%Yb/Y, 3 mm long) and saturable absorber (V:YAG crystal, 2 mm long, initial transmission 86 % @ 1031 nm). The microchip resonator consisted of dielectric mirrors directly deposited on the monolith surfaces (pump mirror
HT @ 968 nm and HR @ 1031 nm on Yb:YAG part, output coupler with reflection 55 % @ 1031 nm on the V:YAG part). For longitudinal CW pumping of Yb:YAG part, a fibre coupled (core diameter 100 mm, NA =0.22, emission
@ 968 nm) laser diode was used. The laser threshold was 3.8 W. The laser slope efficiency for output mean in respect to incident pumping was 16
%. The linearly polarized generated transversal intensity beam profile was close to the fundamental Gaussian mode. The generated pulse length, stable and mostly independent on pumping power, was equal to 1.3 ns (FWHM).
The single pulse energy was increasing with the pumping power and for the maximum pumping 9.7 W it was 78 mJ which corresponds to the pulse peak-power 56 kW. The maximum Yb:YAG/V:YAG microchip laser mean output power of 1 W was reached without observable thermal roll-over. The corresponding Q-switched pulses repetition rate was 13.1 kHz.
9726-75, Session PTue
Conference 9726:
Solid State Lasers XXV: Technology and Devices
Jari Nikkinen, Antti Härkönen, Iiro Leino, Ville-Markus
Korpijärvi, Tampere Univ . of Technology (Finland); Gabriela
Salamu, National Institute for Laser, Plasma and Radiation
Physics (Romania); Mircea Guina, Tampere Univ . of
Technology (Finland)
9726-76, Session PTue
Yongguang Zhao, QIyao Liu, Deyuan Shen, Jiangsu Key
Lab . of Advanced Laser Materials (China)
~4 W continue wave (cw) and ~0.8 mJ pulsed Laguerre-Gaussian (LG) vortex beam at ~1.6 ?m was generated in a simple Er:YAG ceramic solid-state laser resonator pumped with annular beam. A center punched mirror with high-reflected coating at pump wavelength was designed to reshape Gauss pump beam into annular intensity distribution with unaltered M2 parameter and ~68% mode conversion efficiency. After investigating the interference patterns of the doughnut-like output beam by a home-made Mach-Zehnder interferometer, two pure LG01 modes with opposite handedness were found to exist alternately over time, and the dynamical process was detailed analysis. The generated cw and pulsed eye-safe vortex laser with opposite helicity may have novel applications in microparticle manipulation, such as generation of opposite atomic rotational states, as an optical spanner to transmit opposite orbital angular momentum, high-filed laser physics, etc.
9726-78, Session PTue
Artur S . Gouveia-Neto, Marcos V . D . Vermelho, Carlos
Jacinto de Silva, Evandro J . T . A . Gouveia, Univ . Federal de Alagoas (Brazil); Fabia C . Cassanjes, Univ . Federal de
Alfenas (Brazil)
We report a master oscillator-power amplifier (MOPA) system based on 100 ps SESAM Q-switched microchip laser, Nd:YVO4 amplifier and frequencydoubling in bulk LBO crystal. An average power of more than 100 mW is demonstrated at 532 nm corresponding to a repetition rate of ~50 kHz.
Typical conversion efficiency from 1064 nm to 532 nm exceeds 30%. The system has small footprint and does not contain any moving parts. The monolithic master oscillator microchip laser was comprised of a GaAs-based semiconductor saturable absorber mirror and a Nd:YVO4 crystal with a thickness of 100 µm. It delivered a typical average output power in the range of 5 mW at 1064 nm. The seed was subsequently amplified in a Nd:YVO4 bulk amplifier using double-pass configuration increasing the average power beyond 300 mW. Both the seed laser and the amplifier were pumped with low-cost 808 nm laser diodes. A 10-mm long LBO crystal was used to convert the infrared radiation to 532 nm with over 30% efficiency in single pass.
The advantages of the demonstrated light source include short pulse duration, high peak power and simple design. Such compact visible light source could be highly useful for applications including two-photon microscopy, additive manufacturing (two-photon polymerization) and fluorescence lifetime imaging, for example.
Rare-earth doped frequency up-converters have drawn much scientific and technological interest lately owing to their potential application in color displays technology, optical sensing devices, visible solid-state lasers, biological markers, biomedicine, amongst many. Particularly, for applications in biomedicine such as fluorescence based nano-thermometers and fluorescence-based bio-imaging, the penetration depth is a major issue to be considered. Bearing that in mind, it is mostly desirable to produce and/or employ light sources within the two biological windows.
Generation of visible and NIR frequency upconversion emission light within the first biological window spectral region using excitation at 1319 nm in the second biological window in Tm3+/Er3+-codoped TeO2-based glass, is demonstrated. Efficient energy upconversion of cw radiation at 1319 nm into near infrared 800 nm emission in Tm3+ single-doped 60TeO2-
10GeO2-10K2O-10Li2O-10Nb2O5 glass is observed. The 800 nm signal is the sole light emission observed in the entire UV-VIS-NIR spectral region.
Luminescence emission around 1480 nm, and 1800 nm was also observed.
The proposed excitation mechanism for the 800 nm thulium emitting level is assigned to a multiphonon-assisted excitation from the ground-state
3H6 to the 3H5 excited-state level, a rapid relaxation to the 3H4 level and followed by an excited-state absorption of the pump photons mediated by multiphonons connecting the 3H4 level to the 3F4 emitting level. For Tm3+/
Er3+-codoped tellurite glass samples, green(550 nm), red(660 nm) and
NIR(980 nm) owing to erbium ions in addition to the main 800 nm signal originating form thulium ions is readily observed. Here, energy-transfer from Tm3+ (3H6 - 3F4) to Er3+(4I9/2) producing the NIR emission, followed by excited-state absorption of 1319 nm photons populating 2H11/2, 4S3/2, and 4F9/2 visible emitting levels. Erbium single-doped samples did not exhibited visible detectable emissions for excitation powers as high as 1.8
W of cw radiation at 1319 nm. The dependence of the emission signals upon the excitation power, erbium and thulium content and sample temperature is also analysed
16 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9726:
Solid State Lasers XXV: Technology and Devices
9726-79, Session PTue
Artur S . Gouveia-Neto, Univ . Federal de Alagoas (Brazil);
Alexandre O . Silva, Univ . Federal Rural de Pernambuco
(Brazil); Luciano A . Bueno, Univ . de Sorocaba (Brazil);
Carlos Eduardo N Oliveira, Universidade Federal Rural de
Pernambuco (Brazil) dry pressing of spray-dried powders and tape casting, all sintered under high vacuum. The selected geometry of materials was based on numerical simulations. Microstructure of the produced materials was characterized by SEM and EDX with a particular attention to the dopant content across the layers. The optical quality of produced ceramics was characterized and discussed in connection with the microstructure and laser emission results.
Output power of about 7 W and slope efficiency 60 % were obtained in
QCW regime from bilayered 0-10 %Yb:YAG. In the case of multilayered materials higher scattering losses were observed. The comparison between the two processing methods highlighted that the tape-cast materials provided higher optical uniformity and the diffusion zone between the single layers with different dopant content was about 150 nm compared to about 250 nm in samples produced by pressing of powders.
Novel glass materials suitable for the development of infrared excited up-converters have drawn much attention during the last few years.
Fluorogermanate glasses have recently emerged as a viable alternative for photonics and bio-photonics applications owing to the better mechanical strength, chemical durability, and thermal stability when compared to fluoride-based glasses. In addition, these glasses possess the durability and mechanical properties of an oxide glass and the maximum vibrational energy is intermediate (?800 cm-1) between those of silicate (?1100 cm-1) and fluoride (?500 cm-1) based glasses.
The optical properties and energy-transfer upconversion luminescence of
Er3+- and Pr3+/Yb3+-codoped PbGeO3-PbF2-xF2(Mg, Ba) glass under excitation at 980 nm is investigated. In Er3+/Yb3+-codoped samples, green(525, and 550 nm), and red(662 nm), luminescence corresponding to the 2H11/2?4I15/2, 4S3/2?4I15/2 e 4F9/2?4I15/2, respectively, was observed.
A blue signal at 410 nm assigned to the 2H9/2, ? 4I15/2 transition was also detected. The green signals are originated from a nearly resonant energy-transfer involving 2F5/2+4I15/2?2F7/2+4I11/2 process which sustain population of the erbium 4I11/2 level. The erbium green emitting levels were populated through excited-state absorption from the 4I11/2 to the
4F7/2, cross-relaxation 4I11/2+ 4I15/2 ? 4I11/2 + 4F7/2, and energy-transfer
2F5/2+4I11/2 ?2F7/2 +4F7/2. Multiphonon relaxation sustains population in the 2H11/2, and 4S3/2, excited-states, from where radiative decays to the ground-state yield the recorded signals. In the Pr3+/Yb3+ system, emissions around 485, 530, 610, 645, and 725 nm ascribed to the 3P0 - 3HJ
(J=4, 5, and 6), and 3P0 – 3FJ (J=2, and 3,4), transitions, respectively, were observed. The population of the praseodymium upper 3P0 emitting level was accomplished through a combination of ground-state absorption of
Yb3+ ions at the 2F7/2, energy-transfer Yb3+(2F5/2) – Pr3+(3H4), and excited-state absorption of Pr3+ ions provoking the 1G4 – 3P0 transition.
The dependence of the upconversion emission upon glass composition, pump power, heat treatment, and doping contents was also examined
9726-46, Session 9
Jan Hostasa, Laura Esposito, Valentina Biasini, Andreana
Piancastelli, Istituto di Scienza e Tecnologia dei Materiali
Ceramici (Italy); Matteo Vannini, Guido Toci, Istituto
Nazionale di Ottica (Italy)
9726-47, Session 9
Guido Toci, Istituto Nazionale di Ottica (Italy); Angela
Pirri, Istituto di Fisica Applicata Nello Carrara (Italy); Jiang
Li, Tengfei Xie, Yubai Pan, Shanghai Institute of Ceramics
(China); Vladimir Babin, Alena Beitlerová, Martin Nikl,
Institute of Physics of the ASCR, v .v .i . (Czech Republic);
Matteo Vannini, Istituto Nazionale di Ottica (Italy)
Mixed garnets represent an interesting class of laser materials, because their disordered structure broadens the emission spectrum of the lasing ion with respect to their parent materials, resulting in a wider tuning range and an increased capability to generate or amplify ultrashort laser pulses.
In this sense, the mixed Lutetium-Yttrium Aluminum Garnet ((LuxY1x)3Al5O12, LuYAG) was recently proposed in its crystalline form as host for several lasing ions.
We present the optical and spectroscopic characterization and the first example of laser operation of Yb doped LuYAG ceramics, with two different compositions, namely (Lu0.25Y0.75)3Al5O12 and (Lu0.50Y0.50)3Al5O12, both with 15% Yb doping.
Ceramic samples were prepared by reactive sintering from high purity
?-Al2O3, Lu2O3, Y2O3, Yb2O3 powders using Tetraethoxysilane and MgO as sintering aids. After ball milling, the slurry was dried, uniaxially pressed into
20 mm diameter pellets at 20 MPa, and cold isostatically pressed at 200
MPa. Sintering was conducted at 1850 °C for 30 h under vacuum, followed by annealing in air (1500 °C, 10 h) to remove the oxygen vacancies.
Laser test were carried out in a laser cavity end pumped by a fiber coupled diode laser emitting at 936 nm. A slope efficiency as high as 50% with a maximum output power of 6.7 W (in quasi-CW conditions) was obtained from the sample with composition (Lu0.25Y0.75)3Al5O12, whereas the sample with composition (Lu0.50Y0.50)3Al5O12 had a maximum slope efficiency of 34% (due to the higher scattering losses), 3.2 W output power.
The tuning range of the two samples has been characterized.
The use of Yb:YAG ceramic gain media in solid state lasers has been of growing interest for high repetition rate and high power lasers. Probably the most important advantage of ceramic production technology in comparison with that of single crystals is the flexibility of shaping methods that allow the production of near-net-shape components with a well-defined internal structure. In the case of Yb:YAG with dopant distribution designed accordingly to the pumping and cooling geometry the efficiency of the laser device can be enhanced by mitigating thermal lensing effects.
The presented work reports on Yb:YAG transparent ceramics composed of layers with different Yb doping produced by two shaping methods:
9726-48, Session 9
µ
Ronald Stites, Thomas Harris, Air Force Research Lab .
(United States)
In addition to the well-established 5I7 to 5I8 transition at 2.09 µ m in holmium doped laser materials, there also exists a less energetic transition from the 5I6 level to 5I7 at 2.95 µ m. As there has been a recent increase in interest and applications for 3.0 µ m light, this material stands to be a viable alternative to other rare earth doped laser systems. Unfortunately,
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Conference 9726:
Solid State Lasers XXV: Technology and Devices the wavelength required to directly pump the 5I6 level at 1.13 µ m is not convenient for commercial laser diodes. Furthermore, the emission lifetime of the 5I7 state is longer than the 5I6 level, leading to a suppression of lasing due to “bottlenecking” in the material. To overcome these effects, we investigated the activation and deactivation of holmium doped yttrium aluminum garnet (YAG) using ytterbium and praseodymium respectively. By including ytterbium ions in the host material, readily available 940 nm diode light can be used to resonantly excite the 5I6 level in holmium. Similarly, the presence of praseodymium resonantly de-excites the 5I7 state, reducing its lifetime, and making the material more suitable for lasing. Here, we report the absorption and photoluminescence spectra of this triply doped
Yb,Ho,Pr:YAG crystal. In addition, the emission lifetime for both the 2.09 µ m and 2.95 µ m transitions are reported and compared to a Yb,Ho:YAG control sample. Finally, we report progress toward 2.95 µ m laser operation of this
Yb,Ho,Pr:YAG crystal.
9726-49, Session 9
Guido Toci, Antonio Lapucci, Marco Ciofini, Istituto
Nazionale di Ottica (Italy); Laura Esposito, Jan Hostasa,
Istituto di Scienza e Tecnologia dei Materiali Ceramici
(Italy); Leonida A . Gizzi, Luca Labate, Paolo Ferrara,
Istituto Nazionale di Ottica (Italy); Angela Pirri, Istituto di Fisica Applicata Nello Carrara (Italy); Matteo Vannini,
Istituto Nazionale di Ottica (Italy)
Solid hosts doped with elements from the lanthanide series remain as the most heavily utilized method for high energy laser gain. The unique
4f orbitals and the forbidden electronic transitions between the f orbitals
(selection by the Laporte rule) make several lanthanide rare-earth elements
(Ln) attractive for laser emission. The forbidden transitions in the trivalent
Ln ions can be activated by pumping and the decay of electrons from the excited state to the ground state is comparatively slow. This makes it possible to achieve the necessary population inversion required for laser emission. The trivalent Er ion can produce direct emission into the 1540 nm wavelength, thus, it is the rare-earth emitter of choice for many eye-safe applications. In recent years, the need for high beam quality under passive operation in open air applications have renewed interest in Er-doped bulk glasses as the gain material of choice for solid-state eye-safe lasers.
With this target in mind, a study was initiated in order to strengthen a commercially available laser glass by adding modifiers that increase the short-range order in the starting phosphate glass structure. However, it is well known that the addition of the elements that drive the glass stability will decrease the laser gain obtained. It is also known that Er3+ emission is significantly impacted by the host glass phonon energy. Thus, the main goal of the study is to produce a laser gain material that would have an increased thermo-mechanical figure of merit (FOM) while maintaining or increasing any laser FOM’s. This report details the experimental work and the results obtained for optimizing all desired glass properties from a glass laser gain element perspective.
9726-51, Session 10
Soumya Sarang, Oliver Lux, Ondrej Kitzler, Robert
Williams, Aaron McKay, Richard Mildren, Macquarie Univ .
(Australia)
Ceramic-based laser materials are by now a widespread alternative to single crystals, in view of the development of high power laser applications. The flexibility of the ceramic process can be exploited to control the doping distribution, in order to optimize the thermal management of the lasing element.
The laser, optical and spectroscopic properties of multilayer Yb:YAG ceramic structures, differently activated, were investigated. The structures were designed by means of Finite Element Modeling, adjusting the doping distributions to reduce peak temperature, surface deformation and thermally induced stresses, depending on the pump and cooling geometry.
Two ceramic processes were used, i.e. dry pressing of spray-dried powders
(SD) and tape casting (TC), resulting in different defect density and size distribution: TC gives a more uniform transmission, whereas SD results in larger, unevenly scattered defects. The spectroscopic properties were found independent from the production process.
The laser performance has been characterized under high intensity pumping in a longitudinally diode pumped laser cavity, comparing the behavior of the different structures (including homogeneous doping) in terms of slope efficiency, stability under increasing thermal load, spatial uniformity of laser emission. Slope efficiency as high as 60% in Quasi-CW pumping conditions and 55% in CW conditions was measured in bi-layer structures.
The production process and the number of layers influenced the behavior of the samples, in particular the one regarding the spatial uniformity of the laser emission. Samples made by tape casting have shown overall a better thermal stability with respect to samples made by spray drying.
Owing to the high gain coefficient and excellent thermal properties, diamond has enabled efficient Raman frequency conversion of CW lasers in external Raman cavity configurations. While the potential for high power has received much attention, the detailed spectral properties of diamond
Raman lasers have not been thoroughly investigated. One particular area of interest is in generating single-longitudinal mode (SLM) output for highly wavelength-specific applications such as atom cooling and spectroscopy.
Till now, SLM Raman lasers have been realized either in low-power semiconductor spherical microcavities and waveguides or rather complex ring cavities and linear cavities including linewidth narrowing elements.
Here, we report a high-power standing-wave external cavity DRL pumped by a tunable fiber-amplified diode laser of linewidth 50 MHz. Despite the broad Raman gain linewidth (45 GHz) which is about 35 times larger than cavity mode spacing, SLM Stokes output at powers up to 1.2 W was obtained without any intracavity frequency-selective element. This can be attributed to absence of spatial hole burning in Raman lasers as opposed to inversion lasers. Nevertheless, strong mode competition has been observed at higher output powers, leading to multimode operation. The pump wavelength was tunable from 1062.9 to 1064.4 nm by changing the diode seed laser temperature, providing a tuning range of Stokes wavelength from 1237.8 to 1240.2 nm. In addition, since the Raman shift changes with diamond temperature, active temperature control was employed to stabilize and tune the Stokes wavelength with an accuracy of 1.5 pm, thus suppressing mode hopping.
9726-50, Session 9
Simi A . George, SCHOTT North America, Inc . (United
States)
9726-52, Session 10
µ
Simon P . Chard, Cristtel Y . Ramírez-Corral, Powerlase
Photonics Ltd . (United Kingdom); Michael Bass, Ying Chen,
CREOL, The College of Optics and Photonics, Univ . of
18 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9726:
Solid State Lasers XXV: Technology and Devices
Central Florida (United States); Young K . Kwon, Powerlase
Photonics Ltd . (United Kingdom)
High-power visible and UV ultrashort pulse lasers are increasingly in demand for industrial micromachining. For many applications, high energy and low M2 are essential for achieving clean processing by cold ablation.
However, energy scaling of ultrafast laser sources is often limited by nonlinear self-focusing. In this work we present a high-power, high-energy picosecond laser system based on a slab amplifier which has been designed to minimize this effect.
A master oscillator power amplifier system was built using a 5 W passively modelocked seed laser at 1064 nm and multiple ‘Z-slab’ power amplifiers.
The Z-slab is a high aspect ratio Nd:YAG zigzag slab, edge-pumped by a pair of diode arrays. A multi-pass Z-slab was designed for improved high-energy performance by careful optimization of the slab dimensions and beam width to reduce both the B-integral and the effect of thermal distortions on the beam.
The system produced up to 120 W average power at 1064 nm, which was frequency doubled to 84 W at 532 nm. The repetition rate of the seed laser was varied from 250 to 1000 kHz with high beam quality (M2 < 1.4) throughout this range. A maximum energy of 400 µ J was generated in infrared, giving 280 µ J at 532 nm. The pulse duration after the amplifiers was 9.4 ps. The seed laser was also operated in burst mode with bursts of 1 - 10 pulses separated by 33 ns. Over 1 mJ total burst energy was demonstrated at 100 kHz repetition rate at 1064 nm.
The integration of micro-electro-mechanical systems (MEMS) into solid-state laser systems enables extra functionalities for temporal, spectral or spatial tuning of laser characteristics, while simultaneously offering miniaturised, low-cost alternatives to conventional bulk optics used in solid-state lasers.
We will present results showing the Q-switch temporal characteristics of a novel Nd:YAG laser system incorporating two intracavity MEMS micromirrors. This new arrangement extends the functionality of single micromirror based Q-switched solid-state lasers that we, and other research groups, have previously reported. The micromirrors used in our dualmicromirror cavity configuration have different actuation mechanisms: one is electrostatically-controlled for fast resonant scanning at 10 kHz; the other is electrothermally-controlled for slower resonant scanning at 2 kHz or quasi-static displacement. This dual-micromirror technique enables the “fast scan” mirror to control the Q-switch pulse duration. Pulse durations ranging from 30 ns (cavity-limited) up to multiple microseconds can be achieved, with average output powers exceeding 50 mW. Further functionalities, such as pulse burst control or pulse-on-demand control, are achievable through simultaneous actuation of the “slow scan” micromirror.
MEMS can also allow spectral control of solid-state laser outputs. Using an intracavity micromirror and a prism or diffraction grating, the output wavelength of a Yb:KGW laser platform can be tuned by controlling the angular position of the micromirror. We will present initial results on the spectral tuning characteristics, and discuss combining spectral and temporal control using MEMS micromirrors. This combined control could provide avenues for a miniaturised, flexible laser system impacting defence and industrial applications.
9726-54, Session 10
Jesse A . Frantz, Lynda E . Busse, Jasbinder S . Sanghera,
U .S . Naval Research Lab . (United States); Kevin J . Major,
Gopal Sapkota, Menelaos K . Poutous, The Univ . of North
Carolina at Charlotte (United States); Ishwar D . Aggarwal,
Sotera Defense Solutions, Inc . (United States)
Random anti-reflection surface structures (rARSSs) have been shown to increase the transmission of an optical surface to >99.9%. They are an attractive alternative to traditional thin film anti-reflection (AR) coatings for several reasons: They provide AR performance over a larger spectral and angular range; and unlike thin film coatings, they are patterned directly into the optic rather than deposited on its surface. As a result, they are not prone to delamination under thermal cycling that can occur with thin film coatings, and their laser damage thresholds can be considerably higher. In this work, an optimized reactive ion etch procedure was used to pattern rARSSs on fused silica windows, with performance optimized for high energy laser
(HEL) applications at 1.06 µ m. We have demonstrated scale up of this processing technique for windows up to 12” in size. This work represents what we believe to be the largest diameter nanostructured surface on an inorganic material. The windows have been shown to have a laser damage thresholds at 1.06 µ m of >100 J/cm2 – approaching those of the substrate, and approximately five times higher than those of comparable, high quality thin film AR coatings. We present results for the AR properties and uniformity of these large windows.
9726-56, Session 11
Enkeleda Balliu, Magnus Engholm, Mid Sweden Univ .
(Sweden); Lars Norin, Acreo FiberLab (Sweden); Gunnar
Elgcrona, Jonas Hellström, Håkan Karlsson, Cobolt AB
(Sweden)
Our objective in this work is to demonstrate a highly compact, singlefrequency, polarization maintaining CW laser system (MOPA) at 1064nm
(and 532/355 nm by frequency conversion). Our motivation is to reduce the complexity (and cost) of the overall laser system by using only one amplification stage and a few optical components. The overall system is based on a hybrid solid state laser (SSL)/fiber amplifier where a key component is a compact ring-cavity Nd:YAG solid state laser (SSL) operating in single frequency (10 kHz linewidth), with an ultra-low noise and an excellent beam quality. In the present configuration the SSL provides up to 500mW and with a PER of > 30dB but can be designed for power levels up to 3W. The single stage fiber amplifier is constructed by using PM fiber optic components with relatively small core/cladding dimensions of 10/125 um. A short (less than 2 m), custom made, highly Yb-doped fiber (pump absorption >3 dB/m at 920nm) with high photodarkening resistance is used, allowing for reduced non-linear effects (Stimulated Brillouin Scattering).
In the present configuration, a (2+1)x1 PM combiner and two pump LD’s at
976nm (25W) provides SBS free output power levels up to 30W at 1064nm with a PER of more than 20dB. A custom made, anti-reflective coated fused silica endcap (2 x 4mm) is spliced to end of the active fiber. Single-pass, extra-cavity frequency conversion to 532nm (and 355nm) is demonstrated by using different non-linear crystals (LBO, KTP and PPKTP) with conversion efficiencies up to 40%.
9726-55, Session 11
Alan Paterson, Ralf Bauer, Ran Li, Univ . of Strathclyde
(United Kingdom); Caspar Clark, Helia Photonics
Ltd . (United Kingdom); Walter Lubeigt, Deepak
Uttamchandani, Univ . of Strathclyde (United Kingdom)
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9726-57, Session 11
Conference 9726:
Solid State Lasers XXV: Technology and Devices
9726-59, Session 11
Mamoun Wahbeh, Raman Kashyap, Ecole Polytechnique de Montréal (Canada) Brian M . Anderson, Evan Hale, George Venus, Daniel Ott,
Ivan Divliansky, Leonid Glebov, CREOL, The College of
Optics and Photonics, Univ . of Central Florida (United
States)
The design of Q-switched lasers capable of producing pulse widths of
100’s of picoseconds necessitates the cavity length be shorter than a few centimeters. Increasing the amount of energy extracted per pulse requires increasing the mode area of the resonator that for the same cavity length causes exciting higher order transverse modes and decreasing the brightness of the output radiation. To suppress the higher order modes of these multimode resonators while maintaining the compact cavity requires the use of intra-cavity angular filters.
A novel Q-switched laser design is presented using volume transmitting
Bragg gratings (TBGs) as angular filters to suppress the higher order transverse modes. The laser consists of a 5 mm thick slab of Nd:YAG, a 3 mm thick slab of Cr:YAG with a 20% transmission, two orthogonally aligned
TBGs to suppress the higher order modes, and a 40% output coupler. The gratings are recorded in photo-thermo-refractive (PTR) glass, which has a high damage threshold that can withstand both the high peak powers and high average powers present within the resonator. The TBGs recorded in PTR glass have narrow angular selectivity ranging from 0.1 to 10 mrad, and can spatially filter beams with a diameter ranging from 0.1 to 10 mm.
Experimental results are presented demonstrating the Q-switched laser with a cavity length of 1.5 cm, millijoule level output, sub-nanosecond pulse width, and diffraction limited beam quality.
A hybrid laser, based on a C-band semiconductor optical amplifier (SOA) coupled to a long fiber external cavity, is carefully engineered to operate with high spectral purity. The fiber cavity is made of a piece of PM erbium doped fiber, whose one end is sculpted into a biconic lens with an FBG directly written on the other end. The fiber lens has an asymmetric focus, designed to couple the diverging light beam from the SOA into the fiber core with high efficiency. Also, the waveguide of the SOA is tilted relative to the AR facet to suppress axial mode instabilities. Thus combining the attributes of an FBG, erbium doped fiber and semiconductor optical amplifier, a highly stable 2-kHz linewidth single external-cavity mode operating with a SMSR of > 42 dB is demonstrated. Fine tunability of this mode within a single mode-spacing is experimentally achieved. The ability to scan 218 MHz with a frequency-current coefficient of ~2.18 MHz/mA is reported. Moreover by changing temperature of the external fiber Bragg grating, a range of 1.8 GHz is smoothly scanned at a resolution of ~170 MHz and with a frequency-temperature coefficient of 3.1GHz/K. Consequently, the desired operating wavelength can be roughly set by tuning Bragg wavelength and exactly reached via the bias current. A frequency accuracy of ±11 Hz is estimated while the output power at the peak lasing wavelength is measured to be 13.3 dBm. This compact laser with such simple structure and high spectral quality is sought by many segments of industry.
9726-58, Session 11
Hiroki Tanaka, Ryosuke Kariyama, Kodai Iijima, Ryota
Sawada, Fumihiko Kannari, Keio Univ . (Japan)
9726-60, Session 11
Stephen J Beecher, James A Grant-Jacob, Tina L
Parsonage, Ping Hua, Jacob I Mackenzie, Dave P Shepherd,
Robert W Eason, Univ of Southampton (United Kingdom)
We report our recent progress of solid-state lasers directly pumped by
InGaN diode lasers of blue and green. Diode-laser-pumped mode-locked
Ti:sapphire laser and praseodymium-doped LiYF4 lasers are demonstrated.
A blue and green diode lasers deliver output powers of >3.5 W and >1
W. We applied these diode lasers to a Ti:sapphire laser which have been pumped by a frequency-doubled neodymium-doped lasers, and a modelocked Ti:sapphire laser is successfully demonstrated. We confirmed that the green-diode-laser pumping is advantageous compared with blue-diodelaser pumping not only due to the higher Stokes efficiency but also the lack of additional absorption loss which is induced by shorter wavelength pumping.
The praseodymium-doped laser is one of the most successful lasers oscillating in visible region. It can be efficiently and directly pumped by the blue diode laser because it has absorption band around 440 nm. We report a CW operation at 640, 607 and 523 nm from the praseodymium doped
LiYF4 laser, and slope efficiency of >40 % is achieved at 640 and 523 nm. In addition to the CW operation, we demonstrate a Q-switching of the laser at
640 and 607 nm by employing a Cr4+:YAG crystal as a saturable absorber, which have been recognized as a conventional passive Q-switching element for Nd:YAG laser. We finally report a mode-locking of the laser with a semiconductor saturable absorber mirror (SESAM) at 640 nm.
We present details on the fabrication, characterization and laser performance of a Yb:YAG planar waveguide grown by pulsed laser deposition. The 8mm long waveguide features a 15 µ m-thick-core of Yb:YAG grown onto a <100> YAG substrate. In a simple oscillator formed of a mirror highly transmissive for the pump light and highly reflecting for the signal and a 50% reflectivity output coupler, both proximity coupled to opposing waveguide facets, 11.5W of output power was observed with a threshold of
3.0W and a slope efficiency of 47% with respect to absorbed pump power.
The waveguide also oscillated with feedback provided from the Fresnel reflection of ~8% from one of the uncoated facets, but with a significantly higher threshold of 7W. This performance, with output coupling of 92%, highlights the potential suitability of these devices for use as compact high gain amplifiers with very large mode areas, in our case ~20,000 µ m2. Further improvements in performance are expected by increasing the dopant concentration from 1.4 at.% to 3.0 at.% and increasing the pump power.
9726-61, Session 11
A C Butler, P C Shardlow, R T Uren, W A Clarkson,
Optoelectronics Research Centre (United Kingdom)
Laguerre-Gaussian (LG0m) beams are characterised by a donut-shaped intensity profile and have a wide range of applications. One emerging application area is in the field of laser micromachining of materials where the sharper transverse intensity gradient of the ring-shaped beam profile
20 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9726:
Solid State Lasers XXV: Technology and Devices compared to a Gaussian fundamental (TEM00) mode yields better edge definition and edge quality.
In this paper we describe a power-scalable laser architecture for generating
LG0m modes directly in a solid-state laser. Our approach employs a hybrid fiber-laser-pumped Ho:YAG laser, where the pump beam from a Tm fiber laser at 1908 nm is re-shaped to yield a near-field annular profile for the purpose of directly exciting the desired LG0m mode in an end-pumped
Ho:YAG laser. The beam shaping element is a simple silica capillary fiber with air:silica radius ratio of 50%. The output from the capillary fiber is reimaged using an appropriate arrangement of lenses to spatially match the intensity profile of the required LG0m mode in the Ho:YAG laser to achieve preferential lasing on this mode. The combination of a low quantum defect pumping cycle and the ring-shaped pump deposition profile leads to weak thermal lensing opening up the prospect of high lasing efficiency and high output power. We report on preliminary results for direct generation of the first order (LG01) donut mode at 2.1?m and discuss a simple strategy for extending operation to higher order LG0m donut modes.
9726-64, Session 12
Brian Cole, Chris McIntosh, Alan D . Hays, Tom DiLazaro,
Lew Goldberg, U .S . Army RDECOM CERDEC NVESD
(United States)
9726-62, Session 12
Hadiya Jasbeer, Robert Williams, Aaron McKay, Richard
Mildren, Macquarie Univ . (Australia)
The excellent thermal properties of diamond have recently been shown to enable frequency conversion of high-power CW beams with high efficiency and high output beam quality. To date, up to 380 W at efficiencies above
60% have been demonstrated in the infra-red. The typically high intra-cavity
Stokes intensities in these lasers indicates potential for further efficient frequency conversion via second-order parametric processes as a method to generate high power and high brightness visible and UV output at wavelengths important for applications such as laser guide-stars, medical treatments and remote sensing. Here we report intra-cavity frequency doubling of an external cavity diamond Raman laser (EC-DRL) pumped using a Nd:YAG laser at 1064 nm. A lithium triborate crystal was used in a near-concentric EC-DRL to convert the intracavity 1240 nm Stokes field to 620 nm. Pumping of the EC-DRL at power up to 300 W was used with on-time durations limited to 250 micro-seconds to provide a convenient method for demonstrating high power CW conversion. The period is sufficiently long to achieve steady-state thermal gradients in the diamond, thus providing results indicative of genuine CW operation (assuming negligible heat deposition in LBO). To date, we have achieved 2.1 W (ontime power) of 620 nm with 1.4% power conversion efficiency with respect to 1064 nm pump. It is found that careful management of polarization properties of optical elements and nonlinear output coupling are crucial for increasing output power and efficiency, opening up prospects for further power scaling.
9726-63, Session 12
Santanu Basu, Basu Labs Inc . (United States)
Visible lasers with high pulse energy and high repetition rate are required for several important applications such as high-precision material processing and adaptive optics. Fiber lasers are unable to produce high pulse energy due to mode size limitation. In this paper, we will present results of a
Q-switched rotary disk laser that produces 7.5 mJ pulses at 515 nm at 7 kHz repetition rate. The peak power of the green laser is 350 kW. Due to the absence of aberrations in a rotary disk laser, the beam quality is measured to be diffraction limited.
Laser sources in the UV have found utility for Raman based remote sensing applications. For this application, we have explored using a Yb:YAG passively
Q-switched laser, side-pumped by a single bar diode, as a source for the fourth harmonic generation (FHG) at 257.5 nm. Side pumping of Yb:YAG with a pulsed, high peak power (100 W) laser diode bar offers a number of advantages: large pump intensities (>5kW/cm2) for efficient laser operation, a simplicity for resonator design, and compact size.
The compact 30 mm long laser cavity, Q-switched by a Cr:YAG saturable absorber, was operated in a burst mode with the 5 mm pump diode pulsed for 2-4 ms at low duty cycles. Q-switched pulse repetition frequencies varied from 5-20 kHz depending on the Cr:YAG transmission, which was varied from 70% to 85%. Pump duration, pulse repetition frequency and output coupler reflectivity were optimized to yield maximum Yb:YAG laser average power and laser efficiency, while providing sufficient peak intensity, typically 0.3-1 MW, to enable efficient FHG. Pulse energies and durations were in ranges of 1-2 mJ and 2-3ns ranges, respectively. We achieved an optical efficiency of greater than 15% for the Yb:YAG laser.
Extra-cavity 515 nm second harmonic generation (SHG) was achieved using a 5mm long KTP crystal. The 515 nm light was then frequency doubled by focusing it into a 7mm long BBO crystal, resulting in a 20% conversion efficiency from 1030nm to 257.5 nm, with an average UV power greater than
50 mW.
9726-66, Session 12
Satoshi Tanaka, Masaki Arakawa, Atsushi Fuchimukai,
Yoichi Sasaki, Takashi Onose, Yasuhiro Kamba, Hironori
Igarashi, Chen Qu, Mitsuru Tamiya, Shinji Ito, Koji Kakizaki,
Gigaphoton Inc . (Japan); Hongwen Xuan, Yohei Kobayashi,
The Univ . of Tokyo (Japan); Hakaru Mizoguchi, Gigaphoton
Inc . (Japan)
There remains a huge frontier in laser applications because of the constraints of a light source. It is the high power DUV region, in which single photon energy matches the covalent energy levels of various carbon compounds. Considering the absorption spectrum of oxygen, 193 nm is the shortest wavelength suitable for laser processing in air. At 193 nm, however, solid state lasers are difficult to produce even 1 W output, because there is not any durable nonlinear crystal available in the short wavelength region.
As a solution for this frontier, we have been developing a unique hybrid
193 nm ArF laser system which consists of a solid state laser for seeding and an ArF excimer laser for power-boosting. The high coherence quality of the solid state laser can be maintained even after the excimer boosting, enabling superior performance in the fields of interference exposure pattering, ablation process and so forth. The advantage of a solid state laser and that of an excimer compensate each other in this DUV hybrid system.
The solid state laser consists of Yb and Er fiber laser systems and wavelength mixing units [1]. We have got more than 0.3 W output at 6 kHz repetition rate. By seeding the 193 nm laser light into the ArF excimer laser, we have obtained 100 W averaged power with high coherence. In this paper, we will present details of the hybrid laser system and output performance as well as some feasibility test results for various applications.
[1] Hongwen Xuan et al. Optics Express 23, 10564 (2015).
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Conference 9726:
Solid State Lasers XXV: Technology and Devices
9726-67, Session 12
Ahmed Y . Alyamani, King Abdulaziz City for Science and
Technology (Saudi Arabia); Maksim S . Leanenia, National
Academy of Sciences of Belarus (Belarus); Lafi M . Alanazi,
Maher M . Aljohani, Abdulaziz A . Aljariwi, King Abdulaziz
City for Science and Technology (Saudi Arabia); Nikolay
V . Rzheutskij, Evgeniy V . Lutsenko, Gennadiy P . Yablonskii,
National Academy of Sciences of Belarus (Belarus)
Room temperature random lasing with “white” light emission in a mixture of AIIBVI semiconductor powders was achieved for the first time. The scattering gain media was formed by the mixture of closely packed active micron sized crystallites of ZnSe, CdS and CdSSe semiconductors. The micropowders were produced by grinding bulk crystals of each compound.
Optical excitation was performed by 10-nanosecond pulses of tuned
Ti:Al2O3-laser at 390 nm. The lasing in the mixture of semiconductor powders was achieved simultaneously at four wavelengths in blue, green, yellow and red spectral regions after exceeding the threshold excitation power density. A drastic integral intensity increase, spectrum narrowing and appearance of mode structure accompanied the laser action. ZnSe crystallites produce the laser light at about 460 nm while CdS particles
– at about 520 nm. Two types of CdSSe semiconductor micropowders with different sulfur content lase at 580 nm and 660 nm. The threshold excitation power densities for all laser lines in the emission spectrum are approximately the same of about 900 kW/cm2. The sum of the emission spectrum of the mixture of the micropowders forms “white” light with high brightness. Lasing is due to an appearance of random feedback for amplified radiation in the active medium of closely packed light scattering crystallites. The presented results may find their applications in visualization systems, lighting technology, data transmission, medicine as biosensors and in identification systems. The key feature of random lasers is low cost of its production and possibility to be deposited on any type of surface.
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9727-1, Session 1
Amir R . Ali, The German Univ . in Cairo (Egypt) and
Southern Methodist Univ . (United States); Catherine
Elias, Sara Iskander, Khalid Al-Agha, The German Univ . in
Cairo (Egypt); Tindaro Ioppolo, Southern Methodist Univ .
(United States)
This paper presents an interaction study of solvent with the polymeric spheres. When a cross-linked polymer interacts with a solvent the polymer swells. This effect is due to diffusion of polymers and solvent molecules into each other. In turn, that leads to change in the optical and mechanical properties of the polymeric spheres. Several experiments were carried out to study the solvent induced whispering gallery modes (WGM) shift using microsphere immersed in a solvent atmosphere. In the preliminary experiments the microsphere is placed above the surface of three different solvents (Methanol, Ethanol and Hexane) and the measurements of the
WGM shift signal are acquired using a 16 bit DAQ card and recorded on a
PC. Results show the observed WGM shift is mainly due to three effects: (1) change in the index of refraction of the medium surrounding the sphere; (2) change in the index of refraction of the polymer due to solvent diffusion and
(3) change in the microsphere radius due to swelling. This behavior has been examined using preliminary experiments to fully investigate this behavior.
9727-2, Session 1
Daniele Farnesi, Istituto di Fisica Applicata “Nello Carrara”
(Italy) and Museo Storico della Fisica e Ctr . Studi e
Ricerche “Enrico Fermi” (Italy); Francesco Chiavaioli,
Francesco Baldini, Istituto di Fisica Applicata “Nello
Carrara” (Italy); Giancarlo C . Righini, Centro Studi e
Ricerche “E . Fermi” (Italy) and Museo Storico della Fisica e Ctr . Studi e Ricerche “Enrico Fermi” (Italy); Silvia Soria,
Cosimo Trono, Gualtiero Nunzi Conti, Istituto di Fisica
Applicata “Nello Carrara” (Italy)
Fiber optics sensors are ideal transducers for applications requiring devices that are durable, stable and insensitive to external perturbations.
Additionally, they typically provide distributed or quasi-distributed measurement capability at multiple points. The goal of this work was to find an all-in-fiber coupling method to implement a quasi-distributed interrogation of whispering gallery mode (WGM) micro-optical resonators, which are known to exhibit unique properties for sensing. In a previous work, we proposed a configuration based on a long period grating (LPG) written in silica fiber followed by a thick fiber taper (with waist diameters in excess of 15 um), where coupling of cladding modes to WGMs occurs.
This configuration is more robust than the standard fiber taper coupler but it does not allow interrogating more spheres coupled to the same fiber by monitoring the transmitted light. The new approach demonstrated in this work consists of replicating more times the same structure, which includes a second LPG (identical to the first one) that couples back the modulated light into the core. Typical Q-factors of the order of 10^8 and total coupling efficiency up to 60% were measured collecting the resonances of high-Q silica microspheres or microbubbles at the fiber end. Independent addressing of two different resonators at two different wavelengths (1519 nm and 1613 nm) along the same fiber was demonstrated.
9727-3, Session 1
Pengfei Wang, Harbin Engineering Univ . (China);
Ramgopal Madugani, Okinawa Institute of Science and
Technology Graduate Univ . (Japan); Haoyu Zhao, College of Science, Harbin Engineering University (China);
Jonathan Ward, Yong Yang, Light-Matter Interactions Unit,
OIST Graduate University (Japan); Gerald Farrell, Dublin
Institute of Technology (Ireland); Gilberto Brambilla, Univ . of Southampton (United Kingdom); Síle G . NicChormaic,
Okinawa Institute of Science and Technology Graduate
Univ . (Japan)
Previously, microresonator-based add-drop filters have been developed, with silica fiber tapers used to efficiently couple evanescent fields to and from microresonators for their characterization and use. However, it is difficult to maintain stable alignment between microresonators and fiber tapers for an extended period, which is a disadvantage when fabricating add-drop devices for practical, real-world applications. In order to increase the mechanical stability of the microsphere resonator coupling system, in this research, a high quality silica microsphere was first coupled and packaged with two low-loss optical tapered fibers, and their relative positioning was optimized under an optical microscope and then fixed on a microscope slide using a low refractive index UV curable epoxy. The use of a coating epoxy significantly increased the mechanical alignment stability of the microsphere-fiber tapers system. At wavelengths near 1550 nm, a high-Q mode of up to 0.9?105 can be efficiently excited via evanescent coupling from the input tapered silica fiber. The temperature dependence of the packaged silica microsphere add-drop filter has also been investigated.
In order to simplify the fabrication, a one-step fabrication process has been developed using a microsphere coupled to and then packaged with an optical microfiber coupler. Both of the packaging techniques offer the potential to develop low-cost, robustly-assembled fully integrated applications including WDM, sensors, ultra-small optical tunable filters and integrated micro-lasers due to the simplicity of the fabrication process compared with a conventional, costly photolithographic technique.
9727-4, Session 1
(Invited
Paper)
Yuanlin Zheng, Jianjun Cao, Wenjie Wan, Shanghai Jiao
Tong Univ . (China)
Electromagnetically induced transparency (EIT) allows for rendering optical opaque transmission windows to a transparent one under illumination of a second coherent light beam. It was first observed in an atomic gas; intermediately, much attention has been drawn to its unique optical properties including: slowing light, all-optical switching, photon storage,
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etc. This opens up tremendous opportunities for information science.
However, atomic gas systems requires optical cooling or vapor heating techniques combined with vacuum isolation, making it difficult for chipscale integrations. Alternatively, classical analogies mimicking EIT effect are under active pursuit in various physical systems, including coupled resonators, photonic crystals, and plasmonic meta-materials. However, most of them relying on the linear coupling between the resonances, can only exhibit EIT-like spectra but lacking of active-controlled transparency.
Until recently, successful attempts have cloned the idea of EIT in an optomechanical micro-cavity to induce a narrow transparency with the aid of mechanical oscillations excited through Brillouin scattering nonlinearity, which provide phonons to couple some hybrid optical-mechanical resonances, similar to their counterparts: photons in the EIT. Here we report an optically induced transparency (OIT) scheme in a compact micro-cavity in ambient environment by exploring cavity-enhanced four-wave mixing gain to introduce a transparency window in an opaque resonance dip, which directly results from the interference between two resonances coupled nonlinearly through FWM process. Active-controlling of the OIT can be achieved by varying a strong pump beam. Furthermore, OIT observed here is a non-reciprocal one, since FWM gain is a unidirectional one owing to the conservation law of momentum.
9727-5, Session 1
Conference 9727: Laser Resonators,
Microresonators, and Beam Control XVIII
(Invited Paper)
Orel Bechler, Serge Rosenblum, Itay Shomroni, Yulia
Lovsky, Gabriel Guendelman, Barak Dayan, Weizmann
Institute of Science (Israel)
9727-6, Session 2
(Invited Paper)
Andrea M . Armani, Soheil Soltani, Hyungwoo Choi, Vinh
Diep, Andre Kovach, Kelvin Kuo, The Univ . of Southern
California (United States)
High and ultra-quality factor (Q) optical resonators have been used in numerous applications, ranging from biodetection and gyroscopes to nonlinear optics. In the majority of the measurements, the fundamental optical mode is used as it is easy to predict its behavior and subsequent response. However, there are numerous other modes which could give improved performance or offer alternative measurement opportunities.
For example, by using a mode located farther from the device surface, the optical field becomes less susceptible to changes in the environment.
However, selectively exciting a pre-determined, non-fundamental mode or, alternatively, creating a “designer” mode which has one’s ideal properties is extremely challenging. One approach which will be presented is based on engineering a gradient refractive index (GRIN) cavity.
We use a silica ultra-high-Q toroidal cavity as a starting platform device.
On top of this structure, we can controllably deposit, layer or grow different materials of different refractive indices, with nm-scale precision, creating resonators with a GRIN region co-located with the optical field. Slight adjustments in the thicknesses or indices of the films result in large changes in the mode which is most easily excited. Even in this architected structure, we have maintained Q>1 million. Using this approach, we have demonstrated the ability to tune the properties of the device. For example, we have changed the thermal response and the UV response of a device by over an order of magnitude.
9727-7, Session 2
(Invited Paper)
Hong-Bo Sun, Huai-Liang Xu, Xue-Peng Zhan, Qi-Dai Chen,
Jilin Univ . (China)
I will present our progress toward the demonstration of a completely passive scheme for deterministic state transfer between a single photon and a single atom and vice versa. Based on a series of theoretical works [1-5], this scheme relies on a 3-level system coupled to a single mode waveguide
(a single 87Rb atom interacting with a fibre-coupled microsphere resonator in our case). This scheme swaps a flying qubit, encoded in the two possible modes of the photon, with a stationary qubit, encoded in the two ground states of the atom: the state of the incoming photon is mapped to the state of the atom, and the state of the atom is mapped to the state of the outgoing photon [2]. Beyond performing as a passive photonic quantum memory, this scheme can in principle be modified to perform a universal quantum gate [3]. The scheme is completely passive, requiring no control fields beyond the single photons pulses.
In the first experimental realization of this scheme [6], the state of the atom was shown to be determined by the direction of an in-coming single-photon pulse sent through the fiber. The state of the atom was read by a subsequent photon, thereby realizing all-optical switching of single photons by single photons. We then applied this scheme for demonstrating deterministic single-photon extraction from an incoming pulse with arbitrary number of photons [7]. This scheme, which can be applied with any atom-like 3-level L system, provides a building block for scalable quantum networks based on completely passive nodes interconnected and activated solely by single photons.
[1] D. Pinotsi & A. Imamoglu, Phys. Rev. Lett. 100, 093603 (2008)
[2] G. Lin, X. Zou, X. Lin, and G. Guo, Europhysics Letters 86, 30006 (2009)
[3] K. Koshino, S. Ishizaka & Y. Nakamura, Phys. Rev. A 82, 010301(R) (2010)
[4] S. Rosenblum, A.S. Parkins & B. Dayan, Phys. Rev. A 84, 033854 (2011)
[5] S. Rosenblum & B. Dayan, arXiv: quant-ph 1412.0604 (2014) )
[6] I. Shomroni, S. Rosenblum, Y. Lovsky, O. Bechler, G. Guendelman & B.
Dayan, Science 345, 903 (2014)
[7] S. Rosenblum, O. Bechler, Y. Lovski, I. Shomroni, G. Guendelman, and B.
Dayan, under review (2015)
In summary, we have designed and fabricated 3D deformed polymer microcavity by FsLDW via two-photon polymerization, and demonstrated that these microlasers enable high Q-factor and single-mode lasing output with a low lasing threshold at room temperature. From the far field intensity distribution pattern, the deformed microcavities show that they can operate either highly unidirectional emission or single mode output, or both depending on the designs. Because the precise 3D fabrication capability of FsLDW and the good compatibility of polymer to other materials, the realization of the creation of active unidirectional lasers in polymer in this work provides an important step towards the functional integrated organic optoelectronic devices.
9727-8, Session 2
(Invited Paper)
Diederik S . Wiersma, Karlsruher Institut für Technologie
(Germany) and European Lab . for Non-linear
Spectroscopy (Italy) and Consiqlio Nazionale delle
Ricerche-istituto Nazionale di Ottica (Italy)
In this contribution we report on the realization of photonic components with embedded elastomers that deform when they are illuminated with light. This allows to create tunable structures where a light beam influences the optical response of the structure and hence can influence the response to a signal beam. In particular, one can tune efficiently this way the resonance frequency of a high Q resonator, but also create strong (but slow) optical non-linearities
24 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9727: Laser Resonators,
Microresonators, and Beam Control XVIII
9727-9, Session 2
Stephane Calvez, Gaël Lafleur, Clément Arlotti, Alexandre
Larrue, Pierre-Francois Calmon, Alexandre Arnoult,
Guilhem Almuneau, Olivier Gauthier-Lafaye, Lab . d’Analyse et d’Architecture des Systèmes (France) it is possible to realize all-optical modulation on-chip based on the Kerr effect at a record low power of 36 uW. I will also discuss the generation of optical Kerr combs, and talk about the dependence of the input power on the transition from modulation instability, multi-free-spectral range (FSR) mode locking, and 1-FSR mode locking. The hysteresis behavior caused by the optical bistability of a nonlinear cavity plays an important role at the transition between the states; and due to this hysteresis nature, the modelocking state in a low-order FSR is achieved only when we reduce the pump power after strong pumping. I will also describe the competition between four-wave mixing and Raman gain, and will show that the Raman comb becomes dominant during the transition between multi-FSR mode locking states.
Integrated whispering-gallery mode resonators are attractive devices which have found applications as selective filters, low-threshold lasers, high-speed modulators, high-sensitivity sensors and even as nonlinear converters.
Their performance is governed by the level of detrimental (scattering, bulk, bending) loss incurred and the usable loss represented by the coupling rate between the resonator and its access waveguide. Practically, the latter parameter can be more accurately controlled when the resonator lies above the access waveguide, in other words, when the device uses a vertical integration scheme. So far, when using such an integration technique, the process involved a rather technically challenging step being either a planarization or a substrate transfer step.
In this presentation, we propose and demonstrate an alternative method to fabricate vertically-coupled whispering-gallery mode resonators on
III-V semiconductor epitaxial structures which has the benefit of being planarization-free and performed as single-side top-down process. The approach relies on a selective lateral thermal oxidation of aluminium-rich
AlGaAs layers to define the buried access waveguide and enhance the vertical confinement of the whispering-gallery mode into the resonator. As a first experimental proof-of-principle of this approach, 75 µ m-diameter micro-disk devices exhibiting quality factor reaching ~4500 have been successfully made. Further characterization results will be presented at the conference.
9727-12, Session 3
(Invited Paper)
Alexander L . Gaeta, Columbia Univ . (United States)
No Abstract Available
9727-13, Session 4
(Invited Paper)
Victor Brasch, Michael Geiselmann, Martin H . P . Pfeiffer,
Arne Kordts, Maxim Karpov, Hairun Guo, Michail Zervas,
Junqiu Liu, Ecole Polytechnique Fédérale de Lausanne
(Switzerland); Michael L . Gorodetsky, Lomonosov Moscow
State Univ . (Russian Federation) and Russian Quantum
Ctr . (Romania); Tobias J . Kippenberg, Ecole Polytechnique
Fédérale de Lausanne (Switzerland)
9727-10, Session 3
(Invited Paper)
Kerry J . Vahala, California Institute of Technology (United
States)
Two recent applications of nonlinear optics in high-Q microcavity systems will be described. First, the generation of highly coherent light in Brillouin microlaser systems will be examined. Experimental results in which this process is used for rotation sensing is then discussed. Rotation sensitivity of
20 degrees per hour is demonstrated. Second, the generation of frequency combs using dissipative solitons is discussed. Solitons are formed in silica disk resonators at a repetition frequency of 22 GHz. The solitons have a pulse width of 130 fs and are readily broadened. The phase noise of the detected pulse train is low in in the range of a good K-band oscillator.
9727-11, Session 3
(Invited Paper)
Takasumi Tanabe, Takumi Kato, Tomoya Kobatake, Ryo
Suzuki, Akitoshi C Jinnai, Keio Univ . (Japan)
Discovered in 2007, microresonator (Kerr) frequency combs have emerged as an alternative and widely investigated method to synthesize optical frequency combs offering compact form factor, chip-scale integration, multi-gigahertz repetition rates, broad spectral bandwidth and high power per frequency comb line. Since their discovery there has been substantial progress in fundamental understanding and experimental realizations. Yet, in no demonstration could two key properties of optical frequency combs, broad spectral bandwidth and coherence, be achieved simultaneously. Here we overcome this challenge by accessing, for the first time, soliton induced
Cherenkov radiation in an optical microresonator. By continuous wave pumping of a dispersion engineered, planar silicon nitride microresonator, continuously circulating, sub-30 fs short temporal dissipative Kerr solitons are generated that constitute a coherent optical frequency comb in the spectral domain. Emission of soliton induced Cherenkov radiation caused by higher order dispersion broadens the spectral bandwidth to 2/3 of an octave, sufficient for self-referencing and the broadest coherent microresonator frequency comb generated to date. Once generated it is shown that the frequency comb can be fully phase stabilized. The overall relative accuracy of the generated comb with respect to a reference fiber laser frequency comb is measured to be 3*10e-15.
Our findings mark a critical milestone in the development of planar optical frequency combs, enabling applications in e.g. coherent communications, broadband dual comb spectroscopy and Raman spectral imaging.
Our results underscore the utility and effectiveness of planar microresonator frequency comb technology, that offers the potential to make frequency metrology accessible beyond specialized laboratories.
A cavity with an ultrahigh quality factor (Q) and a small size is attractive because it can confine light in a tiny space and allow the strong integration of light and matter. A toroidal microcavity made of silica is of particular interest because it exhibits an ultrahigh Q/V, where V is the mode volume of the cavity. In addition, it can employ the Kerr effect. I will show that
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Conference 9727: Laser Resonators,
Microresonators, and Beam Control XVIII
9727-14, Session 4
(Invited Paper)
Marko Loncar, Pawel M . Latawiec, Vivek Venkataraman,
Michael J . Burek, Harvard School of Engineering and
Applied Sciences (United States)
Owing to its wide bandgap, large linear & nonlinear refractive index, and excellent thermal properties, diamond is well suited for applications in nonlinear and high-power photonics. I will present our work on on-chip diamond frequency combs operating in telecom wavelength range, as well as the efforts aimed at realization of combs operating in the visible.
In addition, I will discuss on-chip Raman lasers that emit at ~2 micron wavelength.
9727-17, Session 5
Yong-Zhen Huang, Ming-Ying Tang, Yue-De Yang, Jin-Long
Xiao, Yun Du, Institute of Semiconductors (China)
Mode selection in square resonator semiconductor microlasers is demonstrated by adjusting the width of the output waveguide coupled to the midpoint of one side. The simulation and experimental results reveal that widely tunable single mode lasing can be realized in square resonator microlasers. Through adjusting the width of the output waveguide, the mode interval of the high-Q modes can reach four times of the longitudinal mode interval. Therefore, mode hopping can be efficiently avoided and the lasing wavelength can be tuned continuously by tuning the injection current.
For a 17.8-?m-side-length square microlaser with a 1.4-?m-width output waveguide, mode-hopping-free single-mode operation is achieved with a continuous tuning range of 9.2 nm.
9727-15, Session 4
(Invited
Paper)
Chee Wei Wong, Shu-Wei Huang, Jinkang Lim, Abhinav
K . Vinod, Jinghui Yang, Univ . of California, Los Angeles
(United States); Heng Zhou, Univ . of Electronic Science and Technology of China (China)
9727-18, Session 5
Andrey B . Matsko, Wei Liang, Danny Eliyahu, Vladimir
Ilchenko, Anatoliy A . Savchenkov, Lute Maleki, OEwaves,
Inc . (United States)
Recent advances in sub-wavelength nanoscale platforms have afforded the control of light from first principles, with impact to ultrafast sciences, optoelectronics and precision measurements. In this talk I will describe recent advances in chip-scale Kerr frequency comb oscillators. Coherent mode-locking is observed in the normal dispersion regime, verified by phase-resolved ultrafast spectroscopy at sub-100-attojoule sensitivities. A phase-locked frequency comb is also achieved over 3,600 modes spanning
65 THz at 18 GHz spacing. The normal dispersion architecture uncovers the mode-locking mechanisms in Kerr frequency combs, matched with firstprinciples coupled-mode theory, complementing our efforts on precision optical clocks.
Miniature radiofrequency (RF) photonic oscillators based on microresonator
Kerr frequency combs generate the highest spectral purity RF signals compared with other electronic and photonic devices with similar size and power consumption. The low spectral frequency phase noise of the Kerr comb oscillators is comparable with the best frequency multiplied ovenized quartz oscillators, while the high spectral purity is similar to the phase noise of the lab scale RF photonic devices. Understanding fundamental limitations on the performance of Kerr comb oscillators is critically important for further development of the technology. In this presentation we review the major known noise sources of the Kerr comb oscillator and discuss possible methods for its improvement.
9727-16, Session 4
(Invited
Paper)
Nan Yu, Jet Propulsion Lab . (United States)
High-Q whispering gallery mode resonators have been mostly studied in the visible and near-IR wavelength regions for optical frequency comb and spectroscopy. With crystalline materials, their use can be extended to the mid-IR beyond 2 µ m where molecular gases not only have very rich characteristic spectral lines but also very large absorption cross sections. In this paper, we describe our continued efforts of pushing whispering gallery mode resonator applications in the MIR wavelength region, including Kerr comb generation and molecular absorption spectroscopy. With a variety of MIR transmitting crystalline materials, we have investigated their Q and limiting factors, dispersion and spectral engineering, parametric oscillation and comb generation. We have also explored the utility and limitation of using high Q resonators for ringdown molecular absorption measurements.
9727-19, Session 5
Silvia Soria Huguet, Istituto di Fisica Applicata Nello
Carrara (Italy); Daniele Farnesi, Istituto di Fisica Applicata
Nello Carrara (Italy) and Museo Storico della Fisica e
Centro Studi e Ricerche “Enrico Fermi” (Italy); Andrea
Barucci, Franco Cosi, Istituto di Fisica Applicata Nello
Carrara (Italy); Giancarlo C . Righini, Istituto di Fisica
Applicata Nello Carrara (Italy) and Museo Storico della
Fisica e Centro Studi e Ricerche “Enrico Fermi” (Italy);
Gualtiero Nunzi Conti, Istituto di Fisica Applicata Nello
Carrara (Italy)
Dielectric microspheres and microbubbles can confine light and sound for a length of time through high quality factor whispering gallery modes
(WGM). We report efficient generation of nonlinear phenomena related to third order optical non-linear susceptibility ?(3) interactions in resonant silica microspheres and microbubbles in the regime of normal dispersion.
The interactions here reported are: Stimulated Raman Scattering (SRS), and four wave mixing processes comprising Stimulated Anti-stokes Raman
26 SPIE Photonics West 2016 · www.spie.org/pw
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Scattering (SARS) and comb generation. SARS is always detected in presence of SRS, and never in the absence of SRS, in agreement with the theory of Bloembergen and Shen. Unusually strong anti-Stokes components and extraordinarily symmetric spectra have been observed. Resonant SARS and SRS corresponding to different Raman bands were also observed. The anti-Stokes Raman components are known to be coupled to the Stokes
Raman ones, even for large dispersion. This coupling results in the growth of the anti-Stokes wave along the microresonator in direct proportion to the Stokes wave through an effectively phase-matched hyper-parametric process. A proof of the cavity-enhanced phenomenon is given by the lack of correlation among the pump, signal and idler: a resonant mode has to exist in order to obtain the pair of signal and idler.
9727-20, Session 5
Conference 9727: Laser Resonators,
Microresonators, and Beam Control XVIII
Guoping Lin, Souleymane Diallo, Yanne K . Chembo,
FEMTO-ST (France) with only ~85 mW pump threshold power in the feeding waveguide is shown along with continuous, mode-hop-free tuning over ~7.5 GHz in a compact, integrated-optics platform.
9727-22, Session 5
(Invited Paper)
Alessia Pasquazi, Marco Peccianti, Univ . of Sussex (United
Kingdom); Sai T . Chu, City Univ . of Hong Kong (Hong
Kong, China); David J . Moss, RMIT Univ . (Australia);
Roberto Morandotti, Institut National de la Recherche
Scientifique (Canada)
Whispering-gallery mode resonators are known to host a wide variety of nonlinear behaviors. In particular, a large body of literature has focused on
Kerr optical frequency combs in recent years. Here we investigate a wider range of nonlinear behaviors, including Brillouin, Raman, and thermo-optical effects. We first perform an experimental investigation in order to evidence the various nonlinear phenomena of interest. Basically, these phenomena involve nonlinear scattering at widely spaced spatial scales, including the electronic (for Kerr), molecular (for Raman), lattice (for Brillouin) and resonator (for thermal) scales. In our study, the host materials are fluoride crystals with a quality factor of the order of one billion at one micron. We then develop various spatiotemporal formalisms in order to investigate these nonlinear phenomena. Our theoretical analysis enables us to explore and understand how extreme events such as thermo-optical relaxation oscillations can be triggered in the resonator. Our study is complemented with numerical simulations that are in full agreement with the experimental findings.
Passive fiber mode-locked lasers enable the excitation of multiple pulses per round trip representing a potential solutions for the increasing demand of practical optical sources with repetition rates of hundreds of GHz or higher.
The control of such high repetition rate regimes is however a challenge. To this purpose, linear filters have been used in an “intracavity” configuration to force the repetition rate of the laser. This design is known as dissipative four wave mixing (DFWM) but it is usually unstable and hence marginally suitable for practical applications.
We explore the use of nonlinear intracavity filters, such as integrated microring resonators, capable of “driving” the FWM interaction in the laser. We term this approach as Filter-Driven FWM.
With a proper choice of the filter properties in terms of free spectral range
(FSR) and Q factor, we could observe stable regimes over a wide range of operating conditions, from high repetition rate oscillation at a 200GHz to the formation of two stable spectral comb replicas separated by the FSR of the main cavity (65MHz). High order filters, moreover, allow achieving nonlinear operation over large passbands. With an 11th order filter we achieve low-frequency mode-locking between the main cavity modes that oscillate within each resonance of the filter, producing burst pulsed operation. A stable mode-locked pulse train at 655GHz with an envelope of
42ps at 6.45MHz is achieved.
9727-21, Session 5
Pawel Latawiec, Vivek Venkataraman, Michael J . Burek,
Harvard Univ . (United States); Birgit J . M . Hausmann,
Lawrence Berkeley National Lab . (United States); Irfan
Bulu, Schlumberger-Doll Research Ctr . (United States);
Marko Lon?ar, Harvard Univ . (United States)
9727-23, Session 6
(Invited
Paper)
Amit Vainsencher, Kevin J Satzinger, Greg A Peairs,
University of California - Santa Barbara (United States);
Andrew N . Cleland, Univ . of California, Santa Barbara
(United States)
Fully integrated microresonator Raman lasers offer the ability to generate unique wavelengths of light on-chip. To date, device demonstrations have been confined to silica and silicon, limiting the scope of generated wavelengths. Here, we introduce an integrated Raman laser based on high quality-factor (>400,000) diamond racetrack resonators. Synthetic singlecrystal diamond is a promising platform for Raman lasers due to its giant
Raman shift (~40 THz), large transparency window (from UV to THz) and excellent thermal properties yielding a greatly enhanced figure-of-merit compared to conventional materials. A polished diamond plate was thinned to specification (<1 ?m) and bonded to a SiO2/Si substrate, after which
~600 ?m path length racetrack resonators were defined via electron-beam lithography. The pattern was transferred to the diamond with an oxygenbased etch chemistry, and polymer coupling pads were aligned to the adiabatically tapered diamond bus waveguides. The demonstrated Raman laser shows a Stokes output discretely tunable over a ~100 nm bandwidth centered around 2 ?m with output powers >250 ?W, extending the functionality of diamond Raman lasers to a wavelength range at the edge of the mid-infrared useful for telecommunication. Continuous-wave operation
We are building nanoscale interfaces to convert coherently between optical and microwave frequencies, ultimately to provide a quantum interface between different qubits operating at microwave frequencies, linked by an optical telecommunications channel. The design is based on piezoelectric optomechanical crystals that co-locate a high quality factor optical and a mechanical resonance in the same sub-micron scale volume, allowing very strong parametric interactions between the two modes. Building these structures from piezoelectric materials allows a strong electromechanical transduction, thus coupling an electric signal at a few GHz to the mechanical resonance at the same frequency. This then allows bilateral parametric coupling between the microwave electrical signal and a 1550 nm telecommunications signal. I will report on progress in this effort.
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Conference 9727: Laser Resonators,
Microresonators, and Beam Control XVIII
9727-24, Session 6
Raphael Dahan, Technion-Israel Institute of Technology
(Israel)
Droplets represent a basic liquid structure that is contained by interfacial tension while bounded almost completely by free surfaces. Such droplets can host three types of resonances: optical-, capillary- and acousticalones. Contrary to their capillary resonances (Rayleigh, 1879) and to optical resonances (Ashkin, 1977), droplets’ acoustical resonances were rarely considered. The challenge lies in the fact that ?droplets’ acoustics requires modulating forces at MHz rates. Here we rely on optical forces (that can act sufficiently quickly) to experimentally excite acoustical resonances at
37 MHz that starts vibrating at an optical threshold of 68 ?W. The optical modes that we are using as a mechanical exciter are circulating in the 40 ?m drop with a ?108 quality-factor. Our results open an experimental access to the acoustical resonances of droplets, which were rarely considered, neither theoretically nor experimentally.
The native shape of the single-mode laser beam used for high power material processing applications is circular with a Gaussian intensity profile.
Manufacturers are now demanding the ability to transform the intensity profile and shape to be compatible with a new generation of advanced processing applications that require much higher precision and control.
We describe the design, fabrication and application of a dual-optic, beamshaping system for single-mode laser sources, that transforms a Gaussian laser beam by remapping – hence field mapping - the intensity profile to create a wide variety of spot shapes including discs, donuts, squares and rectangles. The optic pair transform the intensity distribution and subsequently flatten the phase of the beam, to generate spot sizes and depth of focus close to that of a diffraction limited beam. The field mapping approach to beam-shaping is a refractive solution that does not add speckle to the beam, making it ideal for use with single mode laser sources.
We describe a manufacturing process for refractive optics in fused silica that uses a freeform direct-write process that is especially suited for the fabrication of this type of freeform optic. The beam-shaper described above was manufactured in conventional UV-fused silica using this process. The fabrication process generates a smooth surface (<1nm RMS), leading to laser damage thresholds of greater than 100J/cm2; which is well matched to high power laser sources. Experimental verification of the dual-optic beamshaper will be presented.
9727-25, Session 6
Shai Maayani, Technion-Israel Institute of Technology
(Israel)
We experimentally demonstrate, for the first time, binding of aeroslols with a variety of sizes and shapes in white light. The optomechancial interaction between particles is long range and at the underdamped regime. Incoherency allows mitigation of interference fringes to enable monotonically changing the distance between particles from 60 micron to touching - constituting a parametrically controlled testbed for transition studies at new scales.
9727-28, Session 7
Clémence Jollivet, Kevin F . Farley, Michael Conroy,
Jaroslaw Abramczyk, Nufern (United States); Steffen
Belke, Frank Becker, ROFIN-SINAR Laser GmbH
(Germany); Kanishka Tankala, Nufern (United States)
9727-26, Session 6
Leopoldo L . Martin, Samuel Kaminski, Technion-Israel
Institute of Technology (Israel)
We experimentally demonstrate trapping a micro-droplet with an optical tweezers and then functionalize it as a micro-resonator by bringing it close to a tapered fiber coupler. Our tweezers facilitated tuning of the coupling from the under-coupled to the critical coupling regime with an optical Q of 12 million and micro-resonator size at the 85 um scale. We prove the concept of using an optical trap for activating oil droplets as fiber-coupled micro-resonators. We believe that our technique will extend to several resonators and then to an optical circuit where the shape and position of many optical devices will be controlled.
Our long-term vision includes optical circuits where a multi-minima optical trap shapes and positions multiple resonators. Being practical, we start here with modestly proving this concept by activating one drop as a resonator, and using an optical trap to hold and position it next to a tapered-fiber coupler.
The performance of an ever-increasing number of applications directly depends on the spatial properties of the optical beam such as the shape of its intensity profile and/or its angular divergence. More recently, the strong need for efficient all-fiber beam control techniques has been motivated by the progressive generalization of optical fiber-based systems.
The concepts of transverse mode up-conversion and beam control in allfiber devices are discussed. The shape of the beam emerging the fiber is defined by the shape of the individual transverse modes and their relative fractional power. On the other end, the angular divergence of the output beam, also called the Beam Parameter Product (BPP) depends on the order of the highest transverse mode excited. Therefore, to simultaneously control the beam intensity profile and the BPP, a specific mode scrambling must be achieved in the fiber.
Here, we report a novel specialty fiber designed to tailor transverse mode scrambling in a low-maintenance and cost-effective single-fiber device is reported. Numerical analysis of controlled mode mixing by tailoring the fiber design will be discussed with an emphasis on the high degree of scalability.
Furthermore, the beam control performances will be experimentally demonstrated using a fiber specially designed to transform a single mode
(SM) beam into a flat-top beam with targeted BPP values. Results for fibers with 50, 100 and 200 um core diameters transforming SM laser beams into flat-top beam profiles with BPP values around 2, 4 and 8 mm x mrad respectively will be discussed.
9727-27, Session 7
Paul Blair, Matthew O . Currie, Natalia Trela, Howard
J . Baker, Eoin Murphy, Duncan Walker, Roy McBride,
PowerPhotonic Ltd . (United Kingdom)
9727-29, Session 7
Michael J . Scaggs, Gilbert J . Haas, Haas Laser
28 SPIE Photonics West 2016 · www.spie.org/pw
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Technologies, Inc . (United States)
Conference 9727: Laser Resonators,
Microresonators, and Beam Control XVIII
The ISO 11146-1 standard for measurement of a laser’s M-square requires the minimum measurement of five (5) spatial profiles within the first Rayleigh range and an addition five (5) outside the second Rayleigh range. The first five spatial profiles within the first Rayleigh range establish the beam waist and its location; the second five beyond the second Rayleigh range establish the divergence or convergence from the focusing lens for the M-square computation. The majority of methods used to date are all time averaged and as such are incapable of a real time M-square measurement. We present an ISO 11146-1 compliant method for measuring single shot M-square or beam parameter product values or the measurement of continuous wave sources at rates greater than five frames per second utilizing a pair of GigE based CMOS sensors.
One GigE CMOS sensor is setup to measure the minimum of five spots within the first Rayleigh range for the establishment of the beam waist and its location. A second GigE CMOS sensor is setup to measure the five spatial profiles beyond the second Rayleigh range for the determination of the beam divergence from the focusing lens. Both GigE cameras utilize optics that passively create multiple spatial time slices of the beam and superimpose these time slices on the CMOS sensor in real time resulting in the ability to make single pulse measurements or continuous wave measurements at speeds of greater than five frames per second with full ISO
11146-1 compliance.
9727-31, Session 8
Sebastian Haag, Fraunhofer-Institut für
Produktionstechnologie IPT (Germany); Olaf Ruebenach,
INGENERIC GmbH (Germany); Andreas Beleke,
Fraunhofer-Institut für Produktionstechnologie IPT
(Germany); Tobias Haverkamp, INGENERIC GmbH
(Germany); Tobias Müller, Daniel Zontar, Fraunhofer-
Institut für Produktionstechnologie IPT (Germany);
Christian Wenzel, Innolite GmbH (Germany) and
Fraunhofer-Institut für Produktionstechnologie IPT
(Germany); Christian Brecher, Fraunhofer-Institut für
Produktionstechnologie IPT (Germany)
9727-30, Session 8
Jens Meinschien, Thomas Mitra, Klaus Bagschik, LIMO
Lissotschenko Mikrooptik GmbH (Germany)
A novel micro optical element is introduced allowing coupling of light from several emitters of a laser diode bar into an optical fiber at high brightness.
The approach is unique in terms of a simple design of the laser system in combination with its high brightness. Fiber coupled laser modules of up to
50 W output power from a 100 µ m fiber and NA 0.15 are feasible with just a single mini bar of 10 emitters and the monolithic fiber coupler as only optical element for beam shaping.
Standard configurations for fiber coupling of laser diodes bars require typically multiple optical elements a) for collimation in the fast axis, b) for collimation in the slow axis, c) for rearrangement of beam lets and d) for focusing to the fiber facet. The novel monolithic fiber coupler comprises all these functions into a single element. Special emphasis is drawn on the rearrangement of beam lets to generate a symmetrized beam parameter product which suits to that of the optical fiber.
The monolithic fiber coupler is designed with individual segments for each emitter of the laser diode bar providing two refractive surfaces for each emitter. In principle, beam shaping of the fast axis is done by the first surface whereas beam shaping of the slow axis is done by the second surface. The originally horizontally arranged emitters are rearranged by displacements/tilts of the segments to end up with a vertical stacking of the emitters at the fiber facet.
By means of the monolithic fiber coupler, very cost effective fiber coupled laser diode modules based on bars are feasible. There are several advantages compared to current designs due to the very small number of pieces per laser modules and their small size. Thus, approaches based on laser diodes bars can also compete with single emitter solutions for pumping application due their superior power per pump module combined with inexpensive cost structure with very small numbers of pieces and mounting steps, consequently. Further applications of laser modules with monolithic fiber couplers may also be for direct material processing or as component in projection and illumination systems.
The versatility of products in the market of high-power diode lasers (HPDL) is high. HPDL modules vary in characteristics such as wavelength, form factor, number of emitters, and divergence angles in slow and fast axis.
Most applications require the collimation of the beam emitted by the diode laser. Fiber-coupled laser modules usually require beam homogenization using a beam-tilting unit. Therefore, standard beam-shaping modules for
HPDL consist of fast-axis collimators (FAC), slow-axis collimators (SAC), and a beam-tilting element. The architectures of laser modules from different manufacturers require different arrangements of the optical elements. It becomes obvious that providers of optical modules for HPDL are confronted with a high number of product variants. One flexible way of arranging optical elements for industrial laser production is the use of support structures – sometimes referred to as bottom tabs. The paper presents a flexible module used for the production of beam-shaping optical modules using bottom tabs. The assembly module has been designed for flexibility in order to support the efficient production of beam-shaping product families. Results regarding the achievable precision considering the process capability index and cycle time will be dicsussed.
9727-55, Session PTue
Lebohang T . Bell, Council for Scientific and Industrial
Research (South Africa); Darryl Naidoo, CSIR National
Laser Ctr . (South Africa); Sandile Ngcobo, Council for
Scientific and Industrial Research (South Africa); Andrew
Forbes, Univ . of KwaZulu-Natal (South Africa)
The effects of a temperature gradient in a laser gain medium in an endpumped configuration in a solid-state laser resonator, results in thermally induced aberrations. For our experiment, we measured the thermally induced lens from the coefficient of defocus aberration using a Shack-
Hartmann wavefront sensor. A collimated Gaussian beam at 633 nm was used as a probe beam to an Nd:YAG medium under active pumping, at room temperature. This result is compared to thermal lens determination where the end mirror curvature of an unstable solid state digital laser cavity is varied.
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9727-57, Session PTue
Conference 9727: Laser Resonators,
Microresonators, and Beam Control XVIII
9727-56, Session PTue
Tetsuya Kouno, Shizuoka Univ . (Japan); Katsumi Kishino,
Sophia Univ . (Japan); Masaru Sakai, Univ . of Yamanashi
(Japan); Kazuhiko Hara, Shizuoka Univ . (Japan)
High density GaN-based nano-umbrellas with an optical nanocavity were demonstrated. The GaN-based nano-umbrellas consist of the InGaN curbed hexagonal nanoplates; the diameter and thickness were approximately
200-800 nm and 50 nm, respectively, and GaN nanocolumns supporting the nanoplates; the diameter and height were approximately 50-200 nm and 1500 nm, respectively. As described, nano-umbrellas with various sizes appeared in the arrays. The GaN-based nano-umbrellas were grown on a nitrogen polarity c-plane GaN template by crystal growth technique of radio-frequency plasma-assisted molecular beam epitaxy. The photoluminescence (PL) measurement was carried out at room- (RT-) and low- (t = 4K) (LT) temperature. Each nano-umbrella emitted different colors in the arrays with the RT-PL measurement, resulting that the high density nano-umbrella arrays emitted wide range from approximately 365 to 750 nm wavelengths, and the emission corresponded to white light. The emission color of the nano-umbrellas probably depended on the diameter of the InGaN curbed hexagonal nanoplates. With the LT-PL measurement, many sharp peaks appeared in the wide range emissions of the LT-PL spectra from the high density nano-umbrellas, and the intensities of the sharp peaks nonlinearly increased with increasing the power density of the excitation laser. These sharp peaks were caused by the whispering gallery mode in each InGaN curbed hexagonal nanoplate. In these points, the sharp peaks were probably caused by the lasing actions. These results indicate that high density GaN-based nano-umbrellas are potentially used to white light lasers.
Matthew K . Block, Leidos, Inc . (United States); Leanne J .
Henry, Air Force Research Lab . (United States); Michael
Klopfer, Ravinder Jain, The Univ . of New Mexico (United
States)
There is interest in frequency doubling linearly polarized narrow linewidth
1178 nm for sodium guidestar laser applications. One way of achieving this is through a Raman laser system seeded with both the pump at 1069 nm and narrow linewidth 1178 nm. In this system, 1069 nm is Raman converted to 1121 nm in a resonator cavity having high reflector fiber Bragg gratings (FBGs) centered at 1121 nm. Linewidth broadening in the resonator cavity has been found to result in significant power leakage around the FBGs, decreased
1121 nm power buildup in the resonator cavity, and decreased amplification of 1178 nm. In order to study what impacts this for the lower power stage in polarization maintaining (PM) 10/125 germanosilicate fiber, the effect of cavity length for a fixed FBG bandwidth of 3 nm was investigated. It was found that the effective reflectivity of the FBGs decreased as cavity length increased for a given intracavity 1121 nm power level with saturation at a minimum value occurring for cavity lengths greater than 90 m. Also, for fixed cavity length of 90 m, FBGs having bandwidths of 1, 2, 3, and 5 nm were investigated. It was found that the effective reflectivity of the FBGs decreased for a given 1121 nm intracavity power level as the bandwidth of the FBGs decreased. These results as well as the achieved 1178 nm output power levels and characteristics of both the lower and higher power stages in PM 10/125 and 20/400 germanosilicate fiber, respectively, will be reported.
9727-58, Session PTue
Alan H . Paxton, Air Force Research Lab . (United States)
Closed form solutions are known for the eigenvalues of matrices of the type resulting from the finite-difference approximation to the paraxial wave equation. We discuss the implications of these eigenvalues and the corresponding eigenvectors for obtaining solutions to the wave equation and for obtaining a feel for the form of these solutions.
9727-59, Session PTue
Sandile Ngcobo, Teboho Bell, CSIR National Laser Ctr .
(South Africa)
No Abstract Available
9727-60, Session PTue
Nathália B . Tomazio, Instituto de Física de São Carlos
IFSC-USP (Brazil); Xavier Roselló, Univ . de València
(Spain); Adriano J . G . Otuka, Gustavo F . B . Almeida,
Instituto de Física de São Carlos IFSC-USP (Brazil);
Antonio D . Cremades, Miguel V . Andrés, Univ . de València
(Spain); Cleber R . Mendonça, Instituto de Física de São
Carlos IFSC-USP (Brazil)
Whispering gallery modes microresonators have been attracting increasing interest due to their ability to strongly confine light within small dielectric volumes. This property is quite useful for basic research envolving light-matter interaction and nonlinear optics, but their applications go beyond. The ease of fabrication, on-chip integration and operation at telecommunication frequencies make them suitable for a variety of practical applications, including photonic filters and sensing. In the current work, we demonstrate the fabrication of such resonators via two-photon polymerization. Using this technique, complex 3D structures with submicrometer feature size can be produced. Besides, the flexibility of geometry and the possibility of incorporating a variety of additional materials, such as organic compounds make it a powerful tool for the fabrication of microresonators.
The microstructures we have fabricated are 45 ?m outer diameter hollow microcylinders with sidewall roughness estimated in 100 nm. Light from a 1540 nm-centered broadband source was coupled into the fabricated microresonators via evanescent coupling using a 1.5 ?m waist tapered fiber. The transmitted light is then guided to an optical spectral analyzer, where it was possible to measure resonances, represented as attenuation peaks, with free spectral range of about 9.6 nm. Such microresonators were subsequently functionalized with biopolymers in order to be used as sensors for biological applications.
30 SPIE Photonics West 2016 · www.spie.org/pw
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9727-61, Session PTue
Hoshi Takeshima, Tetsuya Kouno, Shizuoka Univ . (Japan);
Katsumi Kishino, Sophia Univ . (Japan); Masaru Sakai, Univ . of Yamanashi (Japan); Kazuhiko Hara, Shizuoka Univ .
(Japan)
The GaN nanorings were fabricated via nanocrystal growth technique using radio-frequency plasma-assisted molecular beam epitaxy. The outside diameter, ring-width, and height of the nanorings were approximately
900 nm, 150 nm, and 900 nm, respectively. With the room temperature photoluminescence characterization using a nitrogen laser as an excitation source, the sharp peak appeared at 374.5 nm (FWHM: 1.3 nm) and the peak nonlinearly increased with increasing the excitation power. The result indicated that the lasing action was obtained from the nanorings, and the lasing action was caused by the whispering-gallery-mode (WGM); the resonant light propagated in a nanoring with total internal reflection at the boundary of the outside wall of the nanoring. The nanoring lasers were potentially used to the biosensors, because the evanescent component of the WGM is strongly affected by the ambient condition of a nanoring.
Subsequently, the length of the effective resonant path may be changed, resulting in the changing in the lasing wavelength. We examined a sugar sensor based on the GaN nanorings lasers. In the experiment, the lasingwavelengths obtained from the nanorings were investigated with the aqueous solutions with various sucrose concentrations. With the result, the lasing peaks were red-shifted with 2.2 nm where the concentration of aqueous sucrose solution was increased from 31.2 % to 53.7 %. Note that the refractive index of the aqueous sucrose solution increases with increasing its concentration. The results evince that the GaN nanorings potentially used to label-free sugar sensors.
9727-62, Session PTue
Conference 9727: Laser Resonators,
Microresonators, and Beam Control XVIII
Gustav Schweiger, Thomas Weigel, Andreas Ostendorf,
Ruhr-Univ . Bochum (Germany) the light-matter interaction is enhanced inside it. In terms of science and engineering, an interesting use of a WGM cavity is as a coupled cavities system. When two cavity modes are strongly coupled, they are split in the frequency domain and photons are transferred cyclically between the two modes in the time domain. Recently, the time-domain observation and control of the coupling states were reported with photonic crystal nanocavities, and this technology is essential for developing a quantum node and a quantum network. However, such experiments have not yet been achieved with ultra-high Q modes despite the potential benefit to be gained from the use of ultra-high Q cavities.
In this study, we observed strong coupling between ultra-high Q modes in the time domain for the first time. We employed two counter-propagating modes that coupled with each other via surface scattering in a silica toroid microcavity. We employed two tapered fibers (add-drop configuration), one for excitation and the other for observing the energy oscillation between two cavities, which is a necessary technique for directly observing energy in a cavity. The results revealed clear oscillatory behavior, which was induced by the strong coupling. In addition, the oscillation period in the time domain precisely matched that inferred from the mode splitting in the frequency domain, and the measured results showed excellent agreement with those calculated with the developed numerical model.
9727-64, Session PTue
Chao Yang, Guoying Feng, Hong Zhang, Sichuan
University (China); Shouhuan Zhou, North China Research
Institute of Electro-Optics (China)
In this work, we prepared Al nanoparticles/Rh6G doped silica gel and observed random laser action by pumping it with nanosecond laser pulses for the first time. The random laser threshold, the dependence of emission spectra with the outputting direction and the bulk sample’ physical and chemical stability was also experimentally studied. A significant lasing mode centered at 559.7 nm has been observed above the threshold. The intensity of laser emission varies from different directions. The specific output wavelength and remarkable machinability as well as the physical and chemical stability both make it a novel solid-state random laser source for potential applications in biosensors or medical imaging.
Optical microresonators have attracted much interest due to their potential as highly sensitive sensors in a variety of fields, for example as label free biological sensors. For this application the resonator - often a highly transparent microsphere - has to be functionalized by additional surface layers. We present a straight forward theoretical model using geometrical optics to analyze the effect of changes in the resonator properties and the surrounding medium on the resonance wavelength. It is shown that the interaction of the sensor with the surroundings can be expressed by the magnitude of the phase change by total reflection on the resonator surface.
This holds for naked resonators as well as for a resonator with a layer.
9727-65, Session PTue
Alexis V Kudryashov, Julia Sheldakova, Alexey Rukosuev,
Vadim Samarkin, Anna Lylova, Moscow State Univ . of
Mechanical Engineering (Russian Federation)
In this paper we present recent results of formation of different beam intensity distribution by means of bimorph deformable mirrors. We discuss the results of such formation as well as the problems that one faces on this way. A new method for beam structure modification is suggested based on the use of Shack-Hartmann wavefront sensor with the combination of standard M2 meter.
9727-63, Session PTue
Wataru Yoshiki, Zhelun Chen, Keio Univ . (Japan); Tomohiro
Tetsumoto, Shun Fujii, Keio University (Japan); Takasumi
Tanabe, Keio Univ . (Japan)
9727-66, Session PTue
Michael L . Gorodetsky, Lomonosov Moscow State Univ .
(Russian Federation) and Russian Quantum Ctr . (Russian
An ultra-high Q whispering gallery mode (WGM) cavity is attractive because
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Conference 9727: Laser Resonators,
Microresonators, and Beam Control XVIII
Federation); Maxim Karpov, Hairun Guo, Erwan Lucas,
Ecole Polytechnique Fédérale de Lausanne (Switzerland);
G . Lihachev, Lomonosov Moscow State Univ . (Russian
Federation) and Russian Quantum Ctr . (Russian
Federation); Tobias J . Kippenberg, Ecole Polytechnique
Fédérale de Lausanne (Switzerland)
Dissipative Kerr solitons that can be generated in optical microresonators provide stable optical frequency combs and low-jitter femtosecond optical pulses demanded in many applications. We demonstrate a method for nonperturbative real time tracking of dynamical behavior of solitons in microresonators using weak phase modulation of the pump driven by vector network analyzer (VNA) at sweeping frequency. The response function in soliton state demonstrates two resonances. Theoretical analysis using
Lagrangian perturbation approach and numerical simulations reveal that this two-lobe function characterizes detuning of the pump from resonance, the number of solitons, existence domains and proximity to switching points.
Experimental results obtained for two different platforms (integrated SiN microrings and crystalline MgF2 microresonators are in good agreement with theoretical predictions.
challenging because a high degree of indistinguishability requires resonant excitation schemes while electrical pumping using pin-diode structures is intrinsically non-resonant. To tackle this issue we propose an on-chip quantum optics concept where an integrated microlaser resonantly excites a QD-micropillar cavity acting as non-classical light source. As such, our approach combines two very active but so far independent routes of cavity quantum electrodynamics (cQED), namely high-? lasing and single QD lightmatter interaction at the quantum in a novel, integrated device concept.
To be more specific, our on-chip device concept utilize an electrically pumped whispering gallery mode microlaser as in-plane coherent light source which is used for p-shell and strict resonant excitation of an integrated QD-micropillar operating in the weak coupling regime of cQED.
Using this concept, we demonstrate electrically triggered emission of nonclassical light from the QD-micropillar. To this end, our concept also allows for on-chip photon detection and electro-optical feedback, to pave the way for integrated ultra-high bit-rate random number generators.
9727-32, Session 9
Andreas W . Schell, Hideaki Takashima, Yasuko Oe, Shinjiro
Fujita, Shigeki Takeuchi, Kyoto Univ . (Japan)
9727-34, Session 9
Anatoliy Savchenkov, Andrey B . Matsko, Vladimir S .
Ilchenko, Lute Maleki, OEwaves, Inc . (United States)
We describe theoretically, and demonstrate experimentally, power dependent stimulated Rayleigh scattering in monolithic optical resonators.
The effect originates from nonlinear interaction of nearly degenerate high-Q optical modes from two different mode families. It results in total coherent back-reflection of the light coupled to the resonator when the optical power exceeds certain threshold. The effect can be used for tracking and stabilizing optical power as well as for controllable optical gating and modulation.
To efficiently address quantum optical emitters, e.g., nitrogen vacancy centers in diamond or quantum dots, a variety of different micro and nano cavities has been introduced – all of them with specific pros and cons.
Main requirement for the cavities are to have a reasonable high quality factor, good and reliable ways to address and read out the emitter, and the tunability of the system over a broad wavelength range. Here, we will show Nanofiber Bragg grating cavities (NFBCs), which are cavities directly produced on the thin region of tapered optical fibers. Using focused ion beam milling, two Bragg mirrors are created by milling a grating into the fiber, which modulates the effective index of refraction for the guided mode.
The so produced cavities have high quality factors, small mode volumes, allow for highly efficient coupling of the photons directly to the guided mode of the optical fiber, and are easily tunable. We will show experiments of controlled coupling of quantum emitters to NFBCs and show efficient addressing and read out. Performing numerical simulations, we gain insight into the behavior of the cavities and evaluate potential improvements to the cavity design, such as one-sided cavities, in order to further optimize and adjust the NFBCs to different quantum emitters.
9727-35, Session 9
Jintian Lin, Shanghai Institute of Optics and Fine
Mechanics (China); Yingxin Xu, Zhejiang Univ . (China);
Zhiwei Fang, ShanghaiTech Univ . (China); Min Wang,
Shanghai Institute of Optics and Fine Mechanics (China);
Wei Fang, Zhejiang Univ . (China); Ya Cheng, ShanghaiTech
Univ . (China)
9727-33, Session 9
Pierce Munnelly, Matthias M . Karow, Tobias Heindel,
Technische Univ . Berlin (Germany); Martin Kamp, Sven
Höfling, Christian Schneider, Julius-Maximilians-Univ .
Würzburg (Germany); Stephan Reitzenstein, Technische
Univ . Berlin (Germany)
The prospect of studying quantum optics effects in the solid state and the development of quantum light sources for applications in the field of quantum communication has triggered enormous efforts in the fabrication of micro- and nanocavity systems with embedded quantum dots (QDs).
The further development of such quantum devices towards applications in quantum technology focusses to a large extend on the realization of triggered sources of indistinguishable photons and efficient schemes for electrical pumping. Combining these two goals has turned out to be highly
Recently, high-Q microresonators have been fabricated in lithium niobate
(LN) wafer by femtosecond laser direct writing, followed by focused ion beam (FIB) polishing and thermal treatment. The Q factor has reached
2.45?10^6 in the fabricated LN microresonators which is only about one order of magnitude lower than the theoretical limit. Due to the high-Q factor, small mode volume, and large second-order nonlinear susceptibility, the LN microresonators has allowed for second harmonics generation
(SHG) at ultra-low pump powers. It is well known that in the nonlinear frequency conversion processes, phase matching often plays a determining role in terms of the achievable conversion efficiency. However, in a WGM microresonator, it is not straightforward to achieve phase matching because not only the fundamental and second waves should be at least partially phase matched but also their wavelengths must be tuned into resonance with the modes in the microresonators. Here, we overcome the difficulty by controlling the thickness of the LN microdisk and selectively exciting high-order mode of the fundamental wave in the microresonator. Thanks to the low optical absorption and the high nonlinear optical coefficient of LN crystal, we achieve a normalized conversion efficiency of 1.1?10^(-3)/mW.
32 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9727: Laser Resonators,
Microresonators, and Beam Control XVIII
9727-36, Session 9
(Invited
Paper)
Qinghai Song, Harbin Institute of Technology Shenzhen
Graduate School (China)
Recent developments in parity-time (PT) symmetric systems have ushered in unique photonic devices with enhanced functionalities. While singlemode laser emission has been demonstrated in such systems, the current designs face severe challenges in applications, either due to their stringent requirement on fabrication precision or non-scalability to larger devices.
Here we demonstrate a general mechanism to achieve single-mode lasing in coupled cavities, which relies on external mode coupling and overcomes these drawbacks. We find significant gain enhancement for selected modes by external coupling, and our experiments have confirmed the resulting single-mode laser emission in size-mismatched photonic molecules (PMs), when only one constituent cavity is pumped. This behavior persists for a wide range of pump power, from transparent threshold to gain saturation, and it is highly tolerant of fabrication imprecisions. In addition, the output intensity of such single-mode lasers also displays enhancement when compared with the same PMs under uniformly pumping. We believe our results will both advance the understanding of different coupling scenarios in coupled cavities and improve the characteristics of on-chip laser sources for practical applications.
9727-37, Session 10
Amir R . Ali, German Univ . in Cairo (Egypt); Nada El
Ghandoor, Shaimaa El Baklish, The German Univ . in Cairo
(Egypt); Ben Wise, Volkan Ötügen, Tindaro Ioppolo,
Southern Methodist Univ . (United States)
The structure of biopolymers is known to change with temperature, affecting for example the activity of enzymes and the folding of proteins.
We have now shown that such structural change can be monitored using highly sensitive “whispering gallery mode” (WGM) optical biosensors. We devised a technique to temperature-stabilize the WGM sensor system, by adding glycerol to a WGM glass microsphere placed in an aqueous sensing environment. The temperature stabilized WGM sensor was utilized to track structural changes in biopolymers, by monitoring frequency shifts associated with optical polarizability change. Using this sensing method, structural changes in albumin protein (figure) could be resolved for only one degree in temperature variation. Such highly sensitive detection of structural change can have many important applications: in single molecule studies, for thermodynamic investigations of biological systems, and for monitoring temperature-dependent reaction kinetics.
We have improved the time resolution of our biosensing platform, potentially resolving the kinetics of complex molecular systems on timescales ranging from few nanoseconds to several hours.
Asymmetric microspheres allow for free-space coupling and enable “standoff” biosensing and whispering-gallery mode measurements in the far field.
Various unpublished examples for novel single molecule measurements will be shown.
E. Kim, M.R. Foreman, M.D. Baaske, F. Vollmer, “Thermal characterisation of (bio)polymers with a temperature-stabilised whispering gallery mode microsensor” Applied Physics Letters 106, 161101 (2015)
S. Rosenblum, Y. Lovsky, L. Arazi, F. Vollmer, B. Dayan, “Cavity ring-up spectroscopy for ultrafast sensing with optical microresonators” Nature
Communications accepted (2015)
Z. Ballard, M.D. Baaske, F. Vollmer, “Stand-Off Biodetection with Free-Space
Coupled Asymmetric Microsphere Cavities” Sensors 15, 8968-8980 (2015)
M.R. Foreman, J. Swaim, F.Vollmer “Whispering Gallery Mode Sensors” Adv.
Opt. Photon. 7(2), 168-240 (2015)
9727-40, Session 10
(Invited Paper)
Xudong Fan, Univ . of Michigan (United States)
In this paper, we present a new fabrication method for the whispering gallery mode (WGM) micro-sphere based electric field sensor based which allows for longer time periods of sensitivity. Recently, a WGM-based photonic electric field sensor was proposed using a coupled dielectric microsphere-beam. The external electric field imposes an electrtrostriction force on the dielectric beam, deflecting it. The beam, in turn compresses the sphere causing a shift in its WGM. As part of the fabrication process, the PDMS micro-beams and the spheres are curied at high-temperature
(100oC) and subsequently poled by exposing to strong external electric field (~8 MV/m) for two hours. The poling process allows for the deposition of surface charges thereby increasing the electrostriction effect. This methodology is called curing-then-poling (CTP). Although the sensors do become sufficiently sensitive to electric field, they start de-poling after a short period (within ~ 10 minutes) after poling, hence losing sensitivity. In an attempt to mitigate this problem and to lock the polarization for a longer period, we use an alternate methodology whereby the beam is poled and cured simultaneously (curing-while-poling or CWP). The new fabrication method allows for the retention of polarization (and hence, sensitivity to electric field) longer (~ 1500 minutes). An analysis is carried out along with preliminary experiments. Results show that electric fields as small as ~ 100
V/m can be detected with a 300 um diameter sphere sensor a day after poling.
9727-39, Session 10
(Invited Paper)
Frank Vollmer, Max-Planck-Institut für die Physik des Lichts
(Germany)
The optofluidic ring resonator (OFRR) is a thin-walled micron-sized glass capillary that integrates high Q-factor ring resonator (>106) and capillarybased microfluidics. In the OFRR, the circular shaped capillary cross section forms the optical ring resonator that supports the optical whispering gallery modes (WGMs) traveling along the circumference. The WGM has an evanescent field extended into the capillary core, and therefore, interacts with molecules inside the capillary.
This presentation sits at the intersection of photonics, micro/nanofluidics, mechanics, biomedicine, nanobiotechnology, and analytical chemistry, as well as nanoelectronics and fundamental physics. I will start with the introduction of the OFRR, describing its optical and mechanical properties.
Then I will discuss how to utilize the OFRR technology platform in the following vastly different areas: (1) label-free biosensing; (2) microfluidic optomechanics; (3) optofluidic laser; and (4) multi-dimensional microgas chromatography. Finally, if time permits, I will discuss how we expand the OFRR concept, i.e., synergy of photonics and microfluidics, to detect analytes in vapor and liquid phases at the molecular or cellular level for various applications, and to develop novel photonic devices whose performance can be precisely controlled by biological processes and interactions.
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Conference 9727: Laser Resonators,
Microresonators, and Beam Control XVIII
9727-67, Session 10
Rosa Zullo, Antonio Giorgini, Saverio Avino, Pietro Malara,
Paolo De Natale, Gianluca Gagliardi, Istituto Nazionale di
Ottica (Italy)
9727-42, Session 11
Stephen Lane, Peter West, Univ . of Alberta (Canada);
Alexandre François, The Univ . of Adelaide (Australia); Al
Meldrum, Univ . of Alberta (Canada)
Over the last decade, optical whispering-gallery modes (WGMs) have been observed in solid micro-cavities of various geometries and materials showing Q factors higher than 109. These resonators were studied for laser emission, non-linear optics, comb generation and recently proved ultra-sensitive bio-chemical probes. The peculiarity of WGMs supported by dielectric microspheres and toroids is that light travels along closed paths at the interface between the surface of the resonator and the surrounding environment. Unfortunately, most of the light circulates inside the resonator and only a small fraction is actually used for light-matter interaction, thereby reducing the effective cavity enhancement. Here, we propose to use liquid droplets as micro-resonators for sensing applications.
The droplet itself serves as the cavity and the sample at the same time, where the internal optical field is directly used to probe dissolved analytes or particles. We demonstrate free-space excitation and laser frequency locking on whispering-gallery modes in vertically-suspended liquid droplets. The Q-factor limit is investigated by means of cavity photon lifetime measurements performed with cavity ring-down techniques.
Q-factors ranging from 105 to > 107 are observed in the near-infrared and visible spectral regions. Mixtures made from different liquids are also used as a proof-of-concept of chemical sensing. The droplet system appears very promising for applications to spectroscopy, biosensing, material characterization and non-linear optics.
We developed a microfluidic optical resonance biosensor and demonstrated its refractometric and biosensing performance. The device uses the whispering gallery modes (WGMs) that form within a glass capillary whose channel walls are coated with a high-index layer of fluorescent silicon quantum dots (QDs). These cylindrical resonances appear as periodic maxima in the fluorescence spectrum emitted by the quantum dots. Here we utilize the WGMs of a fluorescent core microcapillary for protein detection. The device is comprised of a glass microcapillary with a
50-?m-diameter inner channel coated with a thin film of silicon QDs. Most of the resonant electromagnetic field of the WGMs is contained within the
QD layer but a fraction extends into the capillary channel where it samples a fluidic analyte pumped inside. Changes in the local analyte refractive index cause shifts in the resonant WGM wavelengths, providing the sensing transduction mechanism. The refractometric sensitivity of this device was found to be between 3 and 24 nm per refractive index unit depending on the QD film thickness. Biosensing was demonstrated using the biotin-avidin system, by first functionalizing the channel surface (i.e., the QD film) with amine-terminated polyelectrolyte layers. This fluorescent device showed concentration detection limits on the order of 10 nM, and an equilibrium association constant of 1.1 x 106 M-1 for the biotin-neutravidin interaction.
We then demonstrated the nonspecific binding of vitamin D binding protein as the first step toward developing a microfluidic competition assay for vitamin D.
9727-41, Session 11
(Invited
Paper)
Alper Kiraz, Koç Univ . (Turkey) and Univ . of Michigan
(United States); Qiushu Chen, Univ . of Michigan (United
States); Mehdi Aas, Koç Univ . (Turkey); Alexandr Jonas,
Istanbul Technical Univ . (Turkey); Xudong Fan, Univ . of
Michigan (United States)
We achieved three types of laser emissions with aqueous quantum dots
(QDs) using the same high-Q-factor optofluidic ring resonator (OFRR) platform. In the first type, 2 ?M QDs were in bulk buffer solution that filled the entire OFRR cavity volume. The lasing threshold was 0.1 ?J/mm2, over 3 orders of magnitude lower than the state-of-the-art. In the second type, the
QDs were immobilized as a single layer on the interface between the OFRR inner wall and buffer solution with a surface density as low as 3 ? 109–1010 cm–2. The lasing threshold of 60 ?J/mm2 was achieved. In the third type, we achieved optofluidic FRET lasing using QDs as FRET donors and Cy5 dye molecules as acceptors. We observed lasing from Cy5 emission band in QD-
Cy5 pair when excited at QD absorption band, far away from Cy5 absorption maximum. The demonstrated capability of QDs as donors in FRET lasers greatly improves the versatility for optofluidic laser operation due to the broad and large absorption cross-section of QDs in the blue and UV range.
I will also discuss the comprehensive theoretical analysis of optofluidic
FRET lasers that we have performed based on a Fabry-Perot microcavity using a rate equation model. By comparing FRET lasing-based sensors with conventional sensors using FRET signals obtained by spontaneous fluorescence emission, we show that for optimal pump fluence and
FRET pair concentration, FRET lasing can lead to more than 100-fold enhancement in detection sensitivities of conformation changes for linker lengths in the Förster radius range.
9727-43, Session 11
Jonathan M . Ward, Yong Yang, Síle G . NicChormaic,
Okinawa Institute of Science and Technology Graduate
Univ . (Japan)
Optical sensing of flow in microfluidic systems is an important area of study.
Flow sensing using the concept of a “hot WGM microlaser” is presented.
Silica microcapillary or microbubble whispering gallery resonators were coated with a layer of laser glass, in this case Yb:Er doped phosphate glass.
This was realised by the fact that the two glasses have different melting points. A CO2 laser was used to melt a small piece of doped glass wire onto an 80 µ m silica capillary. The power of the CO2 laser was controlled to flow the doped glass around the capillary. The resulting geometry is a hollow microbottle shaped resonator.
The Er:Yb doped glass outer layer was pumped at 980 nm via a tapered optical fiber and whispering gallery mode (WGM) lasing was recorded at
1535 nm.
Gas was then passed through the capillary and the WGMs were observed to shift towards shorter wavelengths due to the cooling effect of the gas flow.
In this way thermal tuning of the lasing modes over 70 GHz was achieved.
The end of the capillary was connected to a mass flow sensor and the WGM shift rate as a function of flow rate and pump laser power was measured.
Results were fitted using the theory of hot wire anemometry.
Flow sensing can also be realized when the cavity is passively probed at 780 nm. At this wavelength the Q factor of the WGMs was estimated to be in excess of 105.
34 SPIE Photonics West 2016 · www.spie.org/pw
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9727-44, Session 11
Simone Berneschi, Francesco Baldini, Andrea Barucci,
Istituto di Fisica Applicata “Nello Carrara” (Italy);
Alessandro Cosci, Museo Storico della Fisica e Ctr . Studi e Ricerche “Enrico Fermi” (Italy) and Istituto di Fisica
Applicata “Nello Carrara” (Italy); Franco Cosi, Istituto di
Fisica Applicata “Nello Carrara” (Italy); Daniele Farnesi,
Museo Storico della Fisica e Ctr . Studi e Ricerche “Enrico
Fermi” (Italy) and Istituto di Fisica Applicata “Nello
Carrara” (Italy); Gualtiero Nunzi Conti, Istituto di Fisica
Applicata “Nello Carrara” (Italy) and Museo Storico della Fisica e Ctr . Studi e Ricerche “Enrico Fermi” (Italy);
Giancarlo C . Righini, Museo Storico della Fisica e Ctr .
Studi e Ricerche “Enrico Fermi” (Italy); Silvia Soria, Sara
Tombelli, Cosimo Trono, Istituto di Fisica Applicata “Nello
Carrara” (Italy); Stefano Pelli, Istituto di Fisica Applicata
“Nello Carrara” (Italy) and Museo Storico della Fisica e Ctr .
Studi e Ricerche “Enrico Fermi” (Italy); Ambra Giannetti,
Istituto di Fisica Applicata “Nello Carrara” (Italy)
Optical microbubble resonators (OMBRs) are gaining more and more interest as suitable platform for sensing applications because they combine the whispering gallery mode (WGM) resonator properties with an embedded microfluidics. In particular, their operation as optical biosensors is based on the fact that, for a suitable value of the OMBR wall thickness, the WGM optical field extends on both sides of the wall. Therefore the inner surface can be used for the interaction with the analyte inside the flowing fluid and the outer one for the resonance excitation by an external guiding structure (i.e.: a tapered fiber or an optical waveguide). Due to the morphological dependence of the WGMs, any change on the OMBR inner surface related to any biochemical bond causes a shift of the resonances and produces a resonance linewidth broadening with a decrease of the Q factor value. By measuring these changes, information about the concentration of the analyte to be detected can be achieved. A crucial step for the development of an OMBR – based biosensor is constituted by the functionalization of its inner surface. Here we report on the development of an ad-hoc spatially selective photo-chemical procedure, concerning a localized immobilization of fluorescent biomolecules on the OMBR inner surface, able both to maintain high Q factor (> 10^5) for the optical transducer in buffer solution and to guarantee that the OMBR is the unique biosensing element of the overall optical device. The OMBR characterization involves fluorescence microscopy and real time measurement of the resonance broadening.
9727-45, Session 11
Conference 9727: Laser Resonators,
Microresonators, and Beam Control XVIII
Myung-Gi Ji, Byung-Hee Son, Tae-Ryong Kim, Mi Jung,
Chung-Ang Univ . (Korea, Republic of); Hong-Seung Kim,
Chil-Min Kim, Daegu Gyeongbuk Institute of Science
& Technology (Korea, Republic of); Kwang Ryong Oh,
Electronics and Telecommunications Research Institute
(Korea, Republic of); Young-Wan Choi, Chung-Ang Univ .
(Korea, Republic of)
In this paper, we propose a bio-sensing method using optical heterodyne detection based on optical technique for ultra-high Q micro-disk laser
(MDL) as sensor platform. MDL structure with ultra-high Q-factor(~108) has advantages in detecting a small variation of the lasing wavelength.
For example, when a single molecule is attached to sidewall of MDL, the lasing wavelength is changed by sub-pico meter. Optical spectrum analyzer(OSA) has limits to detect sub-pico meter variation in the resonant wavelength because of the spectral resolution. In order to overcome this limitation, we used a heterodyne detection method which needs two MDLs with the same characteristics.
One is used as a reference laser which has a 1550 nm lasing wavelength(?1), and the other laser is used as a sensor for the detection of molecules attached to sidewall of MDL structure. In that case, sub-pico meter variation in lasing wavelength ?1 +?? (sub-pico meter) can be expected.
We performed a heterodyne detection using light beating, and measured ?? changing a sub-pico meter wavelength band to beating frequency ranging from several hundred MHz to several GHz band.
9727-46, Session 11
Shai Maayani, Technion-Israel Institute of Technology
(Israel)
Liquids serve microcavity research ever since Ashkin’s studies on optical resonances in levitating droplets to recent optofluidic resonators. Droplets can provide optical quality factor (Q) in proximity to the limit restricted by water absorption and radiation loss. However, water micro-drops vaporize quickly due to their large area/volume ratio. Here we fabricate a water-air interface that almost entirely surrounds our device, allowing for >1,000,000 recirculations of light (finesse). We sustain the droplets for >16 hours using a nano-water-bridge that extends from the droplet to a practically-unlimited distant-reservoir that compensates for evaporation. Our device exhibits surface tension 8000-times stronger than gravity that self-stabilizes its shape to a degree sufficient to maintain critical coupling as well as to resolve split modes. Our device has 98% of their surrounding walls made strictly of water-air interfaces with concave, convex or saddle geometries, suggesting an arbitrary-shape microfluidic technology with water-walls almost all-over.
9727-47, Session 11
Amir R . Ali, The German Univ . in Cairo (Egypt) and
Southern Methodist Univ . (United States); Andrew
Gatherer, Rice Univ . (United States)
Spinning spherical resonators in the torsional vibrational applications could cause a shift in its whispering gallery mode (WGM). The centripetal force acting on the spinning micro sphere resonator will leads to these
WGM shifts. An analysis and experiment were carried out in this paper to investigate and demonstrate this effect using different polymeric resonators. In this experiment, centripetal force exerted by the DC-Motor on the sphere induces an elastic deformation of the resonator. This in turn induces a shift in the whispering gallery modes of the sphere resonator.
Materials used for the sphere are polydimethylsiloxane (PDMS 60:1 where
60 parts base silicon elastomer to 1 part polymer curing agent by volume) with shear modulus (G=1kPa), (PDMS 10:1) with shear modulus (G=300kPa), polymethylmethacrylate (PMMA, G=2.6*10^9GPa) and silica (G=3*10^10
GPa). The sphere size was kept constant with 1mm in diameter for all above materials. The optical modes of the sphere exit using a tapered single mode optical fiber that is coupled to a distributed feedback laser. The transmission spectrum through the fiber is monitored to detect WGM shifts. The results showed the resonators with smaller shear modulus G experience larger
WGM shift due to the larger mechanical deformation induced by the applied external centripetal force. Also, the results show that angular velocity sensors used in the torsional vibrational applications could be designed using this principle.
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Conference 9727: Laser Resonators,
Microresonators, and Beam Control XVIII
9727-48, Session 12
(Invited Paper)
Andrew Forbes, Bienvenu I . Ndagano, Melanie G . McLaren,
Univ . of the Witwatersrand (South Africa)
Brillouin gain spectrum, the SBS threshold will be enhanced significantly and the power scaling for these narrow linewidth lasers is easier accordingly.
In this paper, we report a kilowatts-level, narrow linewidth, all-fiber format, linearly polarized laser source at 1064 nm in master oscillator-power amplifier (MOPA) configuration. The laser source consists of a linearly polarized, narrow linewidth (~20 GHz) double cladding (DC) fiber laser oscillator and two stages of linearly polarized DC fiber amplifiers. A linearly polarized laser beam with >1kW average power, ~ 35 GHz linewidth, >14.4 dB polarization extinction ratio (PER), and diffraction-limited beam quality
(M2 < 1.1), was achieved. The high power narrow linewidth, transform-limited laser are pretty suited for coherent beam combining, seeding high power
Nd:YAG laser, nonlinear laser frequency conversion, etc.
In the 1990s statistical techniques were applied to laser beams with the result that new measures were introduced to define the beam quality. The moment analysis could be applied to any beam, returning a quantitative measure of its ?quality?. The value of the approach was that the quality could be described by a single number. In this work we apply tools from quantum mechanics to find a single quality factor for how ?vector? a vector beam really is. The applicability of quantum tools to these beams is due to the inherent non-separability of vector beams, a trait they share with entangled quantum states. We show how to practically implement this in the laboratory and show how the approach may be used to monitor degradation in vector beams from lasers, for example, radially polarized laser beams.
9727-51, Session 12
(Invited Paper)
Jean Claude M . Diels, Ladan Arissian, The Univ . of New
Mexico (United States)
9727-49, Session 12
Ji Won Kim, Dong Joon Kim, Eun Jee Park, Hanyang Univ .
(Korea, Republic of); Minjee Jeon, Hanyang Univ . (Korea,
Republic of) and Korea Institute of Industrial Technology
(Korea, Republic of); Hoon Jeong, Korea Institute of
Industrial Technology (Korea, Republic of)
We report a simple technique to allow selective generation of the Laguerre-
Gaussian mode (LG0n) output in an end-pumped Nd:YAG laser. Our approach employs the double resonator configuration, which is composed of two cavities sharing a single gain medium and an input coupling mirror but having two resonating beams of different output coupling with the aid of an intracavity polarizer. Since the population inversion density in the gain medium is determined by the threshold of the first excited cavity (secondary cavity), the other cavity (the primary cavity) using a higher transmittance output coupler cannot lase on the same transverse mode due to the higher threshold level. As a result, we can select the excited transverse mode of the primary cavity simply by controlling the lasing condition of the secondary cavity. Based on this approach, we already demonstrated selective excitation of the fundamental Gaussian TEM00 or the first-order Laguerre-
Gaussian LG01 mode and, moreover, generation of the laser output with a tailored beam profile in an end-pumped Nd:YAG laser. Here, we extend our technique to generate a higher order LG mode output in an Nd:YAG laser yielding the LG01, LG02 or LG03 mode output with well-determined helical wavefronts. The prospects of power scaling and further improvement will be discussed along with the underlying mechanism and the previous results.
Diffraction and atmospheric distortion limits the propagation of laser beams.
“Filamentation was presented as a solution, by self-trapping intense beams, with the transmission limited “only” by nonlinear effects. The “only” evolved in a plethora of parameters to control . . . and understand.
In this field of light matter interaction it becomes difficult to distinguish the controlling from the controlled parameter. The power of the original beam is drained by emission at various wavelengths.
Two types of mechanisms are involved in generating these wavelengths:
(i) emission from individual molecules (self-phase modulation, shock, fluorescence), and (ii) collective mechanisms (four wave mixing, inversion gain) where the new wavelengths are amplified by a group of molecules.
With ultrashort pulses, the amplification at a particular wavelength proceeds along a direction group velocity matching. Resonant amplification occurs when a population inversion is created between electronic, vibrational and rotational levels; inversion affected by molecular orientation, which is in turn controlled by the beam polarization. The filamented beam can be controlled through the seeding process (involving single molecules) and the amplification process. Seeding of new wavelengths is considerably reduced by starting with long, bandwidth limited pulses, and/or a beam waist in vacuum as initial condition. Filaments produced with GHz bandwidth UV pulses are presented, which do not loose energy to “conical emission”. It will be shown how control of the amplification process is made through manipulation of the initial beam polarization. The continuum spectrum, as well spectral lines can be enhanced through polarization control.
9727-52, Session 13
(Invited Paper)
Alexis V . Kudryashov, Moscow State Univ . of Mechanical
Engineering (Russian Federation) 9727-50, Session 12
Wei Shi, Tianjin Univ . (China); Qiang Fang, HFB Photonics,
Inc . (China)
Here we report the design and installation of the largest bimorph deformable mirror (420x480 mm). This mirror is intended to correct for the aberrations of the final amplifier in FIREX laser complex in Osaka University
(Japan). Initial surface and main optical properties of such a mirror are presented. Response functions of all 120 electrodes were investigated. The results of mirror test showed the possibility to build of such kind of mirrors with the size of 500 mm and larger apertures.
High power narrow linewidth linearly polarized fiber lasers have been widely utilized in various applications, such as the nonlinear frequency conversion, coherent laser beam combining etc. The power scaling for the narrow linewidth fiber lasers is challenging mainly due to the limitation from the stimulated Brillouin scattering (SBS). However, when the laser linewidth is broadened to GHz level, which is much greater than the bandwidth of the
36 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9727: Laser Resonators,
Microresonators, and Beam Control XVIII
9727-53, Session 13
Sandile Ngcobo, Teboho Bell, CSIR National Laser Ctr .
(South Africa)
No Abstract Available
9727-54, Session 13
Lebohang T . Bell, Council for Scientific and Industrial
Research (South Africa); Kamel Äit-Ameur, ENSICAEN
(France); Andrew Forbes, Univ . of KwaZulu-Natal (South
Africa); Sandile Ngcobo, Council for Scientific and
Industrial Research (South Africa)
Laguerre-Gaussian, LGpl, modes of radial-order p and azimuthal order l=0 were generated inside the resonator. By using amplitude mask encoded on digital holograms, that were displayed on a spatial light modulator, acting as an end-mirror of the resonator. The digital holograms were encoded to act as an amplitude mask that contained absorbing rings that matched the zeros of the desired Laguerre-Gaussian mode. We show that we can generate LGp0 of p=0 to p=4, when using full circular absorbing rings and also when using half circular absorbingrings. We will demonstrate the advantages associated with using half circular absorbing rings. We observed that the laser resonator will have a lower threshold, while at the same time maintain the same laser characteristics. The characteristics such as; slope efficiency, mode purity and beam quality factor.
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9728-1, Session 1
(Invited Paper)
Iyad Dajani, Angel Flores, Roger H . Holten, Thomas
Ehrenreich, Air Force Research Lab . (United States)
In contrast to stimulated Brillouin scattering (SBS) where larger mode field areas can lead to greater suppression in fiber amplifiers, the modal instability (MI) threshold is typically reduced with increased core sizes.
Consequently, the fiber SBS/modal instability threshold tradeoff plays a key role for further power scaling. We report results from two ~1.5kW, all-fiber
Yb-doped amplifiers with comparable optical to optical efficiencies and effective linewidths; one with a 25 µ m core fiber from Nufern and one with a 20 µ m core fiber from LEIKKI. SBS suppression in both amplifiers was achieved through pseudo-random bit sequence (PRBS) phase modulation which has proved to be more effective than white noise source. Both amplifiers can provide fringe visibilities >90% when a sample of the output is coherently combined with a low power channel. While the power output from the 25 µ m core fiber was MI limited at ~1.5 kW, no sign of MI was observed in the smaller core fiber. Furthermore, there were strong indications that the Brillouin gain coefficient was substantially lower in the
20 µ m core fiber. Overall, this may allow us to utilize the higher MI threshold
20 µ m fiber to scale further in power while maintaining sufficiently narrow linewidth for either coherent or spectral beam combination. Finally, as a demonstration of the combinability of multiple kW class amplifiers driven by
PRBS phase modulation, we coherently combined 5 commercial amplifiers using a 1x5 diffractive optical element leading to a 5 kW beam with a measured M2 value of 1.06. The combining efficiency was 82%.
9728-3, Session 1
Nader A . Naderi, Angel Flores, Kenneth B . Rowland Jr .,
Iyad Dajani, Air Force Research Lab . (United States)
Development of Yb-doped fiber lasers has seen rapid progress with emerging wide range of applications. Operating at shorter wavelengths of the gain bandwidth is desired due to lower quantum defect heating which may be beneficial in suppressing the modal instability (MI), and in order to expand the wavelength range in spectral beam combining architectures. To date, high-power narrow-linewidth monolithic fiber amplifiers operating at wavelengths <1040 nm are much less developed compared to their 1060 nm counterparts. We report here on a kilowatt narrow-linewidth monolithic fiber amplifier operating at 1034 nm. To suppress SBS, the single-frequency master oscillator was phase modulated using pseudo-random bit sequence
(PRBS) format. By utilizing a band pass filter and a WDM, as well as by optimizing the length of fiber used in the pre-amplifier stages, we were able to appreciably suppress unwanted lasing. The pre-amplifier was spliced onto a mode field adapter (MFA) followed by a (6+1)?1 tapered fiber bundle
(TFB). The high-power stage was powered by six ?250 W pump diodes centered at 976 nm. The final stage consisted of ~8 meters of a conventional non-PM 25/400 µ m Yb-doped fiber from Nufern. The output of the amplifier was terminated with a cladding mode stripper and an endcap. With an optimal PRBS pattern set at a clock rate of 4.4 GHz, we demonstrated 1 kilowatt of power with a slope efficiency of 84% and an ASE content of <3%.
Beam quality measurements at 1 kilowatt provided M2 values of 1.09-1.17 with no sign of modal instability.
9728-2, Session 1
µ
Simon S . Duval, Michel Olivier, Vincent Fortin, Martin
Bernier, Michel Piché, Réal Vallée, Ctr . d’Optique,
Photonique et Laser (Canada)
The direct generation of high-peak-power femtosecond pulses from a compact and efficient source in the mid-infrared spectral region (2-20 µ m) is of great interest for ultrabroad and ultrasensitive spectroscopy in the molecular fingerprint region as well as for medical and defense applications.
Recently, we demonstrated the first mid-infrared femtosecond fiber laser operating at a wavelength above the transparency limit of silica fibers. This mode-locked fiber ring laser emitting at 2.8 µ m is based on an erbiumdoped double-clad fluoride fiber. Mode locking is achieved via nonlinear polarization evolution through the use of a quarter waveplate, a half waveplate and an optical isolator that also acts as a polarizer. End caps are spliced on both ends of the fluoride fiber to prevent fiber tip degradation and ensure long term mode-locked operation. We introduce here an improved cavity design based on numerical simulations. By adjusting the output coupling and the erbium-doped fiber length, 294-fs pulses with a peak power of 10.1 kW are generated at a repetition rate of 96.5 MHz. Since water vapor has an important absorption band around 2.8 µ m, the impact of the intracavity atmospheric absorption on the laser dynamics is also discussed. Numerical simulations, which agree well with the experimental results, suggest that the generation of 150-fs pulses with peak powers above
20 kW should be feasible without intracavity dispersion compensation.
9728-4, Session 1
Nader A . Naderi, Iyad Dajani, Angel Flores, Air Force
Research Lab . (United States)
Recent advances in power scaling of narrow-linewidth monolithic fiber amplifiers have made them suitable candidates for many applications including coherent beam combination for directed energy platforms.
One major obstacle to power scaling of narrow-linewidth fiber amplifiers, however, is the onset of stimulated Brillouin scattering (SBS) which is the lowest threshold nonlinear process for such amplifiers. Over the past decade, several effective SBS mitigation techniques including the application of phase modulation and thermal gradients have been demonstrated. Another novel approach is based on the laser gain competition technique which relies on seeding the amplifier with two laser sources; one broadband while the other is narrow-linewidth possessing a longer wavelength. The SBS suppressing mechanism behind this technique relies on reduction of the effective length of the amplifier due to a sudden rise in the narrow-linewidth signal at the output end of the fiber. One key advantage of laser gain competition approach is its compatibility with other SBS mitigation techniques such as phase modulation and thermal gradient. In this study, we investigate power scaling of a two-tone Yb-doped monolithic fiber amplifier seeded with 1064 nm narrow-linewidth light along with spectrally broader 1034 nm light. For further SBS suppression, pseudorandom bit sequence (PRBS) phase modulation was applied. A factor of
13 dB in SBS threshold enhancement was realized at a PRBS clock rate of 2.5 GHz; leading to 1 kW of output power at 1064 nm with 81% optical
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efficiency. The beam quality was near the diffraction limit with no sign of modal instability.
9728-5, Session 1
Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
Yasuhiro Mashiko, Huy K . Nguyen, Masahiro Kashiwagi,
Tomoharu Kitabayashi, Kensuke Shima, Daiichiro Tanaka,
Fujikura Ltd . (Japan) available wavelengths. High power operation of such amplifiers with narrow linewidth seed signals is frequently limited by non-linear effects and higher order mode instabilities of output beam due to an interaction between the fundamental mode and higher order modes. In this paper we report a development of fiber amplifier with >1.5kW output power and M2-value of the beam <1.2 in broad wavelength band from 1030nm to 1070nm for 15GHz linewidth and up to 3m output delivery cable. The fiber amplifier with direct laser diode pumping in the ruggedized compact modular package has 40% wall-plug efficiency. The maximum output power of the broadband amplifier at longer wavelength edge of the band was limited by mode instability effects. The spectral dependence of higher order mode instability threshold and quantum defect heating are described and discussed.
A 2 kw single-mode fiber laser with a 20-m long delivery fiber and high back reflection resistance has been demonstrated. An Yb-doped fiber with large core size and differential modal gain is used to realize high
SRS suppression and single-mode operation simultaneously. A length of a delivery fiber is 20 m that gives flexibility to the design of processing systems. An output power of 2 kW is achieved at a pump power of 2.86 kW.
A slope efficiency is 70%. The Stokes light power by SRS is more than 50 dB below the laser light power at the output power of 2 kW even with a 20-m delivery fiber. Nearly diffraction-limited beam quality is also confirmed (M2
= 1.2). An output power of 3 kW is believed to be achieved by increasing pump power. The back reflection resistance properties of the fabricated single-mode fiber laser are evaluated numerically by SRS gain calculated from measured laser output spectra and fiber characteristics. Acceptable power of coupling light back into the delivery fiber is 500 W which is high enough for processing of highly reflective materials. The output power fluctuation caused by SRS and back reflection in materials processing will be well suppressed. Our high power single-mode fiber lasers can provide high quality and stable processing of highly reflective materials.
9728-8, Session 2
Jae M . Daniel, Defence Science and Technology Group
(Australia) and Aether Photonics Ltd . (Australia); Nikita
Simakov, Defence Science and Technology Group
(Australia) and Univ . of Southampton (United Kingdom);
Alexander V . Hemming, Defence Science and Technology
Group (Australia); W . A . Clarkson, Univ . of Southampton
(United Kingdom); John Haub, Defence Science and
Technology Group (Australia)
9728-6, Session 1
Charles X . Yu, Oleg Shatrovoy, Tso Yee Fan, MIT Lincoln
Lab . (United States)
We present results from a Yb fiber amplifier pumped by an ultrahigh brightness pump. The pump outputs 2 kW in a 200 µ m, 0.2 NA multi-mode fiber. The pump utilizes wavelength-beam combining technology from
Teradiode Inc. Two gain fibers have been utilized. Both fibers have MFD of
17 ?m. The high brightness enables relatively short gain fibers, 3-4 meters, while maintaining excellent pump absorption of 19 dB. The maximum fiber amplifier output power is 1350 W, limited by multimode instability, with 90%
O-O efficiency and diffraction-limited BQ. The fiber amplifier linewidth is 3
GHz at 1050 W.
We present a novel metal coated triple clad active fibre design, utilising an all glass inner cladding structure and aluminium outer coating. This metal coated active fibre enables a number of benefits to high power laser design, such as increase robustness and extended operating temperature range.
As a demonstration of the advantages of this design a passively cooled ytterbium fibre laser is presented. Consisting of a 20 m length of active fibre coiled into a planar arrangement and mounted onto a high emissivity heatsink. Up to 405 W of output power was achieved without the need for active water or forced air cooling. The slope efficiency of this source was 74
% and maximum outer heat sink temperature was ~140°C. This arrangement allowed for significant weight and size savings to be achieved with the active fibre laser head weighing less than 100 g. We will discuss the design choices and trade-offs of metal coated active fibre on high power fibre laser systems as well as the prospects for further power scaling to the kW level.
9728-9, Session 2
Yang Xu, Wei Shi, Tianjin Univ . (China); Qiang Fang, HFB
Photonics, Inc . (China)
9728-7, Session 2
Roman Yagodkin, Nikolai Platonov, Alexander Yusim,
Valentin P . Gapontsev, IPG Photonics Corp . (United States)
Fiber laser output power scaling with near diffraction limited beam to
100s of kilowatts through spectral beam combining requires kW level fiber amplifiers with wide gain bandwidth and low nonlinearity for narrow linewidth seed amplification. Yb-doped fiber amplifier with diffractionlimited beam and direct laser diode pumping is a remarkable source of CW IR radiation distinguished by high efficiency and broad range of
We demonstrate a monolithic continuous wave (CW) fiber laser source at
1070.25 nm, producing 2 kW laser power with very narrow spectral linewidth
(<0.3 nm) and near diffraction-limited beam quality (M2 =~1.3). The laser consists of a CW fiber laser oscillator and two double cladding (DC) fiber amplifier in the master oscillator-power amplifier (MOPA) configuration. The master ocillator is a distributed Bragg reflected (DBR) fiber laser, producing
~ 6 W laser power with <0.1nm spectral linewidth. The two double cladding fiber amplifiers were developed to enhance the laser power up to ~200W and ~2050 W, respectively. The optical to optical efficiency of the main amplifier reach 84.8%. Under the full power output, the 3-dB linewidth and
20-dB linewidth of the laser emission spectrum was 0.28 nm and 1.2 nm respectively. The all-fiber construction of the 2kW near diffraction-limited laser source allows compact size, no maintenance and robust operation and thus enables various practical applications in industrial material processing
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications and especially in the laser combining due to the pretty narrow spectral linewidth. and fiber oscillators. The guidelines derived from the simulations do not involve changes in the composition of the active material (except for its doping concentration), but they can still lead to a significant increase of the transverse mode instability threshold. The dependence of this parameter on the active ion concentration, the core conformation, the pump configuration
(co-, counter- or bi-propagating pump) and wavelength or the mirror reflectivities in a fiber oscillator among others will be studied and discussed.
9728-10, Session 3
(Invited
Paper)
Oleg L . Antipov, Institute of Applied Physics of the RAS
(Russian Federation); Maxim S . Kuznetsov, Institute of Applied Physics of the RAS (Russian Federation) and N .I . Lobachevsky State Univ . of Nizhni Novgorod
(Russian Federation); Valentin A . Tyrtyshnyy, IRE-Polus
Co . (Russian Federation); Dmitry Alekseev, IRE-Polus Co .
(Russian Federation) and Moscow Institute of Physics and
Technology (Russian Federation); Oleg I . Vershinin, IRE-
Polus Co (Russian Federation)
Mode instability (MI) in Yb-doped fiber amplifiers attracted great interest in the last years. This effect was referred to nonlinear transformation of power from the intense fundamental mode LP01 to the initially-weak higher-order modes. The MI was observed both in large mode area fibers with large core diameter and in few-mode fibers with a relatively small core. Two mechanisms of formation of refractive index gratings caused by population inversion (due to polarizability difference of the excited and unexcited Yb3+ ions) and temperature distributions induced by the modes interference field were discussed as the main reason for the MI. This paper is devoted to the detailed experimental investigation and theoretical modeling of the MI effect in Yb-doped fibers with core diameter of 8-10 um. The influence of a backward propagating wave (due to a backward reflection or scattering) on the MI threshold and a temporal behavior of the output power was investigated. The MI threshold was registered at 1-100 Watts pump power.
The threshold was found to decrease dramatically in the presence of a backward reflection; an increase of the signal bandwidth or input power resulted in increase of the MI threshold. Numerical simulation revealed self-consistent growth of the higher-order mode and traveling electronic index grating accompanying the population grating induced by the mode interference field (due to different polarizability of the excited and unexcited
Yb3+ ions).
9728-12, Session 3
Arlee V . Smith, Jesse J . Smith, AS-Photonics, LLC (United
States)
Previously we developed a model of mode instability in Yb-doped fiber amplifiers based on the process of stimulated thermal Rayleigh scattering.
Here we extend the model to treat Tm-doped fiber amplifiers pumped at 790 nm and including a strong cross relaxation process to populate the upper laser level. The quantum defect heating in such Tm fiber is approximately four times greater than in Yb fiber. At first glance this suggests much lower mode instability thresholds for Tm fibers. However, strong population saturation in Tm counteracts the greater heating, and leads to higher thresholds in Tm than in Yb fibers.
We model Tm operating at 2040 nm and Yb fibers operating at 1060 nm. Other properties are as much alike as possible to achieve a direct comparison of mode instability in the two fibers. This comparison uses 4 meter long 25/400 ?m core/cladding diameter fiber with equal V numbers
(5.92) and with the doping levels adjusted for equal pump absorption. The doping levels were (NYb = 1.05E26/m3) and (NTm = 6.0E26/m3). At this doping level the cross relaxation in Tm increased the power efficiency from
39% to 62%. The fibers were co- and counter-pumped at 976 nm (Yb) and
790 nm (Tm), both seeded with 6 W input signal. For co-pumped amplifiers, signal output power at threshold was found to be 20% higher in Tm than Yb; for counter-pumped 45% higher.
9728-13, Session 3
Shadi A . Naderi, Ball Aerospace & Technologies Corp .
(United States); Iyad Dajani, Jacob Grosek, Timothy
Madden, Air Force Research Lab . (United States)
9728-11, Session 3
Cesar Jauregui-Misas, Hans-Jürgen Otto, Friedrich-
Schiller-Univ . Jena (Germany); Sven Breitkopf, Friedrich-
Schiller-Univ Jena (Germany); Jens Limpert, Friedrich-
Schiller-Univ . Jena (Germany); Andreas Tünnermann,
Fraunhofer-Institut für Angewandte Optik und
Feinmechanik (Germany)
The average output power of Yb-doped fiber laser systems is currently limited by the onset of transverse mode instabilities. Besides, it has been recently shown that the transverse mode instability threshold can be significantly reduced by the presence of photodarkening in the fiber. Therefore, reducing the photodarkening level of the core material composition is the most straightforward way to increase the output average power of fiber laser systems but, unfortunately, this is not always easy or possible. In this paper we present guidelines to optimize the output average power of fiber laser systems affected by transverse mode instabilities and photodarkening. The study is focused not only on power amplifiers but also, for the first time to the best of our knowledge, on double-pass amplifiers
It is well-known that the onset of the modal instability (MI) is a limiting factor for achieving higher powers in Yb-doped fiber amplifiers with good beam quality. In this paper, we present simulation results for MI in an alternate gain medium; a core-pumped Raman fiber amplifier (RFA). Raman amplification in silica is broad and tunable and thus Raman fiber lasers can offer access to wavelengths that are inaccessible via rare-earth-doped fiber lasers. Furthermore, since the core of a Raman fiber does not contain rare earth elements, photodarkening is not present and fabrication is relatively easy. A system of equations is derived to represent the transfer of energy in core-pumped RFAs and the simulation results are presented. Similar to Ybdoped fiber amplifiers, heat generated in a Raman fiber amplifier primarily derives from the quantum defect, and time-dependent oscillations in the temperature ultimately cause the fundamental mode to transfer energy to higher-order transverse modes; thus degrading the beam quality of the amplifier output. The modal interference in the pump can also lead to a travelling index of refraction grating. Consequently, our model allows for propagating gratings that may be written by either pump or signal. Using this model, dependence of MI threshold on the Raman gain in a corepumped RFA is discussed. The gain tailored design is shown to be effective only if the outer region has significantly lower Raman gain. Finally, the effect
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications of cross interactions on MI due to the presence of two gratings is discussed in detail.
Bigot, Lab . de Physique des Lasers, Atomes et Molécules
(France)
9728-14, Session 3
Hans-Jürgen Otto, Cesar Jauregui, Friedrich-Schiller-
Univ . Jena (Germany); Jens Limpert, Friedrich-Schiller-
Univ . Jena (Germany) and Helmholtz-Institute Jena
(Germany); Andreas Tünnermann, Friedrich-Schiller-Univ .
Jena (Germany) and Helmholtz-Institute Jena (Germany) and Fraunhofer-Institut für Angewandte Optik und
Feinmechanik (Germany)
The maximum average power that can be emitted from an ytterbium-based fiber-laser system is estimated. The analysis takes into account all the effects known so far that may limit the average power including transverse mode instabilities and photodarkening. Hereby, the recent finding that transverse mode instabilities depend on the average heat load is exploited. The results of this analysis show that there are three main limiting effects: stimulated
Raman scattering, the brightness of the pump laser and transverse mode instabilities. Moreover, it seems feasible, disregarding possible practical constrains, that the average output power can be significantly increased to
50kW and beyond when following the proposed optimizations.
9728-16, Session 4
Benjamin G . Ward, U .S . Air Force Academy (United States)
Large mode area fiber is a well-known solution to prevent the appearance of nonlinear effects that impede the rise of the optical power in fiber lasers.
Solid Core Photonic Bandgap Fibers (SC-PBGF) have shown over the last few years their potential to give access to large effective mode area. They are easy to splice and can be doped with rare-earth ions, their spectral properties enabling, for example, spectral filtering for high-power laser. We report on the design and the fabrication of a new all-solid Bragg fiber based on the pixelization and heterostructuration of its cladding. Pixelization is a discretization of the high index rings that compose the cladding to get true photonic bandgap guidance and heterostructuration consists in removing some of these “pixels” so as to increase the losses of higher order modes
(HOM) by “sieve” effect. The cladding is made of only two high index rings. The thickness of the low index ring as well as the heterostructuration
(its symmetry and the number of removed pixels) have been chosen to maximize the HOM confinement losses (above 10 dB/m) while keeping the fundamental mode losses low (below 0.1 dB/m). Single mode behavior has been confirmed experimentally even for short fiber length kept straight.
The proposed geometry allows to have access to different MFD from 48
µ m to 60 µ m at 1 µ m wavelength by drawing the same stack with different core radius. As a result, a record MFD of 60 µ m is obtained in the case of
SC-PBGF.
9728-18, Session 4
Aurélien Benoit, Romain Dauliat, Dia Darwich, Raphaël
Jamier, XLIM Institut de Recherche (France); Stephan
Grimm, Jens Kobelke, Kay Schuster, Leibniz-Institut für
Photonische Technologien e .V . (Germany); Philippe Roy,
XLIM Institut de Recherche (France)
Rod-type photonic crystal fiber amplifiers show tremendous potential to enable high peak and average output powers by virtue of their large mode field area and strong mode discrimination properties. In such fibers, employing a large-pitch air hole lattice causes higher order transverse modes to become delocalized thus reducing their overlap with the amplifying core of the fiber, and minimizing the gain they experience.
Due to the extremely low effective numerical aperture of the core, the delocalization mechanism is very sensitive to thermal lensing in high average power amplifier configurations exhibiting significant heat loads.
In these situations, the thermal lensing may distort the fundamental mode enough to influence the resulting heating distribution thus affecting simultaneously several key amplifier parameters such as local population inversions, mode field areas, and effective intermodal intensity overlap.
These parameters affect both the fundamental mode output characteristics as well as power transfer to higher order transverse modes caused by stimulated thermal Rayleigh scattering. This paper describes a method of accurately modeling these amplifiers taking into account a converged solution to the thermo-optic feedback loop. This method also accounts for the possibility of asymmetric doping profiles and directly treats higher order mode STRS gain competition along the entire length of the amplifier.
Example applications are described. This approach enables further fiber design optimization for higher yet peak and average power outputs.
Since the double-clad fiber architectures development, fiber-based laser have witnessed an impressive power scaling. The extracted power rising has been accompanied by the development of Very Large Mode
Area (VLMA) fiber designs allowing overcome some key hurdles like the non-linear process or photo-darkening. However, due to the very large core size of fiber architectures, a new phenomenon, referring to modal instabilities, has been evidenced recently like the current limitation which hampers any further power increase in the field of fiber laser sources without a dramatic degradation of the emitted beam quality. In order to push away the appearance power threshold of this limitation, new aperiodic cladding microstructurations have been proposed to improve the higher-order modes (HOM) rejection out of the gain region and then to optimize the amplification of the sole fundamental mode. These aperiodic microstructures have proved recently their potential to enhance an efficient
HOM delocalization enabling singlemode confinement in the core region with passive VLMA fibers.
In this communication we report on the first high power emission demonstration obtained using a solid non-filamented core fully-aperiodic large pitch fiber manufactured by the REPUSIL method based on the sintering and vitrification of micrometric doped silica powders. Using a simple laser cavity, an average output power of 233 W was achieved with an available pump power of 400 W for the first time in such a fiber. The preliminary M2 measurements have shown an excellent beam quality with values less than 1.4.
9728-17, Session 4
Jean-Paul Yehouessi, Géraud Bouwmans, Olivier Vanvincq,
Andy Cassez, Rémi Habert, Yves Quiquempois, Laurent
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
9728-19, Session 4
µ
Mette M . Johansen, Technical Univ . of Denmark (Denmark);
Mattia Michieletto, Technical Univ . of Denmark (Denmark) and NKT Photonics A/S (Denmark); Torben Kristensen,
Thomas T . Alkeskjold, NKT Photonics A/S (Denmark);
Jesper Lægsgaard, Technical Univ . of Denmark (Denmark)
Ytterbium-doped silica based fiber lasers and amplifiers can generate megawatts of peak power and hundreds of watts in average power using direct amplification. Achievements of higher extracted output power have led to observations of transverse mode instabilities (TMIs) above a system and fiber dependent average power threshold. TMI significantly degrades beam quality and constitutes an impediment to future power scaling. High power operations of rod fiber amplifiers cause the TMI threshold to degrade probably related to photodarkening and increased core absorption.
In this work we test an improved version of the DMF rod fiber with an 85 µ m core and a 260 µ m pump air cladding in a high power setup. The improved
DMF rod fiber delivers 350W of stable extracted output limited by the available pump power. To our knowledge, this is the highest achieved stable average output power from a 1m rod fiber amplifier, and an increase of
25% compared with the first generation DMF rod fiber. The slope efficiency was measured to 70%, and a maximum of 71% optical to optical efficiency was obtained. The first generation DMF rod fiber was operated in the leaky regime, whereas the improved DMF rod fiber is operated in the guiding regime resulting in higher core confinement and improved beam quality. The improved DMF rod fiber is tested several times allowing the fiber to degrade due to photodarkening, and also causing the TMI threshold to degrade from
>360W to ~290W.
9728-21, Session 5
(Invited Paper)
Darren D . Hudson, The Univ . of Sydney (Australia)
Ultrashort pulse generation in mid-Infrared fiber lasers operating near 3 µ m has become a hot topic of research. In this talk, we cover the rise of ultrafast fiber lasers in this exciting wavelength range.
Using a saturable absorber mirror in a Er:ZBLAN fiber laser, we demonstrated the first stably mode-locked 3 µ m class fiber laser in 2014, which generated 6 ps pulses with a peak power of > 0.5 kW. More recently, we employed nonlinear polarization rotation based mode-locking in this system. Using a mid-IR Frequency Resolved Optical Gating technique, we measured 500 fs pulses, with a peak power of > 6 kW. The leap to subps operation of these lasers systems opens the door for a wide range of exciting applications and experiments including mid-IR supercontinuum generation, mid-IR fiber based frequency combs, human tissue surgery, and sensitive broadband trace gas detection.
Here, we review the progress from initial Q-switched laser systems generating 100 ns pulses with < 0.1 kW peak power all the way to the subps, multi-kW level mode-locked systems. The potential for these systems to be a driver for mid-IR fiber laser frequency comb sources is explored in detail, including calculations of supercontinuum and coherence. Finally, a view towards the future of ultrashort pulse generation in these systems is presented, with a particular emphasis on creating sub-100 fs gainbandwidth limited pulses directly from the oscillator.
9728-20, Session 5
(Invited Paper)
Anna C . Peacock, Li Shen, Fariza H . H . Suhailin, Univ . of
Southampton (United Kingdom); Natasha Vukovic, Univ of Southampton (United Kingdom); Noel Healy, Univ . of
Southampton (United Kingdom)
9728-22, Session 5
µ
µ
(Invited Paper)
Reza Salem, Thorlabs Quantum Electronics (United
States); Zhuo Jiang, Dongfeng Liu, Robert M . Pafchek, Paul
Foy, Mohammed Saad, Doug Jenkins, Alex E . Cable, Peter
Fendel, Thorlabs Inc . (United States)
The nascent field of semiconductor optical fibers is attracting increased interest as a means to exploit the optoelectronic functionality of the semiconductor materials directly within the fiber geometry [1]. Compared to their planar counterparts, this new class of waveguide retains many of the advantageous properties of the fiber platforms such as robustness, flexibility, cylindrical symmetry, and long waveguide lengths. Furthermore, owing to the large Kerr nonlinearity of the materials, fibers with semiconductors embedded in the core are also ideal for the development of integrated nonlinear optical devices. In this paper we review our progress in characterizing the transmission properties of the semiconductor fibers and demonstrate their use in nonlinear applications. Particular focus will be placed on fibers with a hydrogenated amorphous silicon (a-Si:H) core as this material offers several favorable properties such as high nonlinear coefficients, low fabrication costs, and low transmission losses. Exploiting these features, we have demonstrated an array of nonlinear processes in the fibers including ultrafast optical switching, modulation and broadband continuum generation. Although many of the first generation semiconductor fibers have been fabricated with relatively large micron sized cores, by scaling these down towards the nanoscale dimensions used on-chip the nonlinear effects will be enhanced, paving the way for the development of low power, high speed all-fiber systems.
[1] A.C. Peacock, J.R. Sparks, and N. Healy, “Semiconductor optical fibres: progress and opportunities,” Laser & Photonics Reviews 8, 53?72 (2014).
We report mid-infrared supercontinuum (SC) generation in a dispersionengineered step-index indium fluoride fiber pumped by a femtosecond fiber laser around 2 µ m. The SC spans 1.8 octaves from 1.25 µ m to 4.6 µ m with an average output power of 270 mW. The pump source is an all-fiber femtosecond laser that generates sub-100-fs pulses at 50 MHz repetition rate with 570 mW average power. The SC-generation fiber is engineered through core size and numerical aperture adjustments to have a zerodispersion wavelength close to 1.9 µ m. The fiber dispersion is calculated to be small and anomalous at the pump wavelength and to maintain a small absolute value (<7 ps/nm.km) over the mid-infrared region from 2 um to 4.5 um. Two fiber lengths of 30 cm and 55 cm are selected for the
SC generation experiments based on the numerical modelling results.
The measured spectra and the numerical modelling results are presented showing good agreement for both lengths. The femtosecond pumping regime is a key requirement for generating a coherent SC. We show by modelling that the SC is coherent for a pump with the same pulse width and energy as our fiber laser and added quantum-limited noise. The results are promising for the realization of coherent and high-repetition-rate SC sources, two conditions that are critical for spectroscopy applications using
FTIR spectrometers. Additionally, the entire SC system is built using optical fibers with similar core diameters, which enables integration into a compact platform.
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9728-24, Session 5
Christian Gaida, Martin Gebhardt, Fabian Stutzki, Hans-
Jürgen Otto, Cesar Jauregui, Jens Limpert, Friedrich-
Schiller-Univ . Jena (Germany); Andreas Tünnermann,
Fraunhofer-Institut für Angewandte Optik und
Feinmechanik (Germany)
We analyze the average power scaling capabilities of Tm-based fiber lasers in the context of transverse mode instabilities. Based on very fundamental scaling laws for the guiding properties of optical fibers, a four times higher critical thermal load for the operation at 2 µ m wavelength in comparison to 1 µ m systems can be expected prior to the onset of transverse mode instabilities. While for Yb-based systems critical thermal loads of 30-35 W/m have been demonstrated, an average thermal load of more than 120 W/m can be expected for Tm-based systems. In order to validate this hypothesis a high average power experiment was realized with a 1.2 m long Tm-doped large-pitch fiber as main amplifier, which was bi-directionally pumped. A pump-limited average output power of 248 W with a slope efficiency of more than 40% has been achieved. Heating of mirrors, coatings and the ambient atmosphere have been mitigated to maintain a Gaussian-like wellconfined beam profile. A detailed simulation of the thermal conditions in this fiber amplifier reveals an average thermal load of more than 100 W/m, which is more than three times higher than the critical value for state-ofthe-art near-diffraction limited systems operating around 1 µ m. Based on the current understanding of transverse mode instabilities in combination with the experimental results presented herein, the expected average power limits for various Tm-doped fibers can be predicted. Strategies for the optimization of Tm-based fiber laser systems, with respect to the fiber length, cross-relaxation and excited-state pumping, will be discussed.
9728-25, Session 6
Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
Tobias Tiess, Saher Junaid, Martin Becker, Manfred
Rothhardt, Leibniz-Institut für Photonische Technologien e .V . (Germany); Hartmut Bartelt, Leibniz-Institut für
Photonische Technologien e .V . (Germany) and Abbe
School of Photonics (Germany); Matthias L . Jäger, Leibniz-
Institut für Photonische Technologien e .V . (Germany)
9728-26, Session 6
Saniye Sinem Yilmaz, Laser Zentrum Hannover e .V .
(Germany) and Bilkent Univ . (Turkey); Christoph
Ottenhues, Thomas Theeg, Laser Zentrum Hannover e .V . (Germany); Samir Lamrini, Karsten Scholle, Michael
Schaefer, Peter Fuhrberg, LISA Laser Products OHG
(Germany); Hakan Sayinc, Laser Zentrum Hannover e .V .
(Germany); Fatih Ömer Ilday, Bilkent Univ . (Turkey);
Jörg Neumann, Laser Zentrum Hannover e .V . (Germany);
Ludger Overmeyer, Institut für Transport- und
Automatisierungstechnik (Germany); Dietmar Kracht,
Laser Zentrum Hannover e .V . (Germany)
Thulium doped fiber lasers are being shown to be suitable for addressing a range of applications in both pulsed and CW mode of operation at this wavelength range. Over the last decade, the power scaling of 2 µ m sources has been demonstrated by 790 nm diode pumped thulium doped fiber lasers. These lasers have achieved kW power levels, as well as high power narrow line-width demonstrations of more than 600 W. Active and passive fibers supporting higher order modes were employed in such sources, leading to the degradation of the beam quality. A promising alternative approach is spectral beam combining of laser sources by using WDMs
(wavelength division multiplexer) developed from truly single mode fiber for power scaling while simultaneously maintaining the excellent beam quality.
Since many applications increasingly require high power thulium-doped fiber lasers with distinct wavelengths, spectral beam combination is a key technology, which must be further explored and developed.
We demonstrate an in-house-made WDM cascade for spatially combining signals and scaling up the laser power available from a truly single mode fiber. The experimental setup contains four identical continuous wave oscillators each emitting narrow line-width signals at three distinct wavelengths, which are 1920 nm, 1950 nm, 1977 nm and 2030 nm. These lasers are combined by using in-house-made WDMs and we achieved output power of more than 38 W with a combining efficiency of 80 %.
Future work will include investigations on power scaling of the used individual laser sources and explore dense spectral combination with WDM cascades.
Over the past years, Thulium-(Tm-) doped fiber lasers in the 2 µ m region have gained lots of interest due to many potential applications in material processing and biophotonics. Based on the broad gain regions spanning from 1800nm to 2100nm, they offer the perfect basis to implement broadly tunable and user-friendly light sources like they are increasingly demanded in spectroscopic applications. Recently, a novel tuning mechanism based on a FBG array as versatile spectral filter has been reported combining a unique spectral freedom for customized tuning ranges and ultrabroad bandwidths with a fiber-integrated setup in order to maintain the advantages of the waveguide geometry. In this work, we demonstrate such a dispersion-tuned and pulsed fiber laser in the Tm domain around 1950nm using a modulator and a discrete FBG array to control the emission wavelength. In order to comply with the demands of potential applications in biophotonics, for the first time, this tuning concept is realized in a polarization-maintaining (PM) configuration ensuring linearly polarized output. While a simple FBG array is employed containing 5 gratings inscribed in PM fiber, we also discuss the possibility to implement FBGs inscribed in standard single mode fiber.
Based on a tuning range of 58nm, the emission characteristics of the system are investigated showing pulse durations of around 15ns and a good spectral signal contrast. In order to highlight the prospect for tunable high-power operation, we have also implemented a single-pass amplification stage. In such a MOPA configuration, the average power is scaled to more than 25W.
9728-27, Session 6
Till Walbaum, Matthias Heinzig, Fraunhofer-Institut für
Angewandte Optik und Feinmechanik (Germany); Franz
Beier, Fraunhofer-Institut für Angewandte Optik und
Feinmechanik (Germany) and Institute of Applied Physics,
Friedrich-Schiller-University Jena (Germany); Andreas
Liem, Thomas Schreiber, Ramona Eberhardt, Fraunhofer-
Institut für Angewandte Optik und Feinmechanik
(Germany); Andreas Tünnermann, Fraunhofer-Institut für
Angewandte Optik und Feinmechanik (Germany) and
Institute of Applied Physics, Friedrich-Schiller-University
Jena (Germany)
We present measurements of the temperature increase inside the active fiber of a thulium fiber amplifier during high power operation. At a pump power of over 100 W at 793 nm, we measure the core temperature
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications distribution along the first section of a large mode area (LMA) highly thulium doped active fiber by use of an optical backscatter reflectometer.
A mode field adaptor is used to maintain single mode operation in the
LMA fiber, which is ensured by beam quality measurement. An increase in temperature of over 100 K can be observed in spite of conductive cooling, located at the pumped fiber end and jeopardizing the fiber coating. The recoated splice can be clearly identified as the hottest fiber region. This allows us to estimate the maximum thermally acceptable pump power for this amplifier.
We also observe that the temperature can be decreased by increasing the seed power, which is in agreement with theoretical predictions on the increase of cross relaxation efficiency by depletion of the upper laser level.
This underlines the role of power scaling of the respective seed power of a thulium amplifier stage as a means of thermal management.
of producing high power pulses typically use free-space propagation or non-PM fibers but suffer from obvious environmental limitations. In an effort to increase the output power delivered by all-fiber Tm oscillators, high repetition rate cavities (as high as 611MHz) have been used. But such systems, which cannot use pulse-picking devices, are not suitable for many application requiring few MHz repetition rates.
In this contribution we present an all integrated all-PM laser system with the potential to deliver femtosecond pulses after external recompression.
It is, to the best of our knowledge, the first net-normal cavity all-PM Tm fiber oscillator. Our source has a very good (few percent) short and long term stability. By design it delivers long pulses which allow for direct amplification in a multi-stage system. This all-fiber all-integrated MOPA system producing 60ps, 6W average power, pulses at 20MHz is an ideal seed for supercontinuum generation. The current system is limited by the available pump diodes. The booster stage has an efficiency of 40%, which is
10% higher than similar amplification stages already published.
We will present at the conference the various laser and MOPA architectures we have developed together with their performances and stability.
9728-28, Session 6
Nikita Simakov, Defence Science and Technology Group
(Australia) and Univ . of Southampton (United Kingdom);
Jae M . O . Daniel, Defence Science and Technology Group
(Australia); Jon D . Ward, Gooch & Housego plc (United
Kingdom); W . Andrew Clarkson, Univ . of Southampton
(United Kingdom); Alexander V . Hemming, John Haub,
Defence Science and Technology Group (Australia)
9728-30, Session 6
Alex M . Sincore, Lawrence Shah, CREOL, The College of
Optics and Photonics, Univ . of Central Florida (United
States); Vadim Smirnov, OptiGrate Corp . (United States);
Martin C . Richardson, CREOL, The College of Optics and
Photonics, Univ . of Central Florida (United States) Sources in the 2.1?m wavelength region are required for numerous applications including remote sensing, LIDAR, free-space optical communications and for pumping mid-infrared optical parametric oscillators. In some instances it is desirable to be able to tune the wavelength of the 2.1?m source and such tuning can be achieved by mechanically rotating an etalon or diffraction grating. These mechanical components, while suitable for swept wavelength sources, are typically less reliable when rapid wavelength switching is desired due to the inertia associated with the rotation of the mechanical arrangement. Intra-cavity, all fiber etalons have less inertia, however these components are limited in peak power handling and sensitive to external temperature fluctuations. All of these elements also suffer from the problem that switching to another position involves a transition where the wavelength selective element is resonant at unwanted wavelengths.
Recently, acousto-optic tunable filters (AOTFs) have attracted substantial attention as a wavelength selective element in the 2 µ m range. The AOTF used in this report enables an electronically-controlled and inertia-free wavelength selective filter with a response FWHM of 1 nm. We incorporated this filter as a wavelength selective element in a holmium-doped fiber laser cavity and demonstrated a digitally-controlled wavelength agile source operating in the atmospheric transmission window around 2.1
µ m. We will discuss the operation in various regimes such as wavelength sweeping, switching and tuning. Finally we will discuss the power scaling of such sources and potential utility in generating wavelength agile mid-infrared sources.
High brightness, high power 2-micron laser sources are necessary for directed energy, spectroscopic sensing, medical applications, and generating mid-IR light via nonlinear processes. In the last ten years, such applications have increasingly relied upon lasers based on silica fiber doped with thulium
(1.7 – 2.1 ?m) and holmium (2.05 – 2.15 ?m). In general, Tm:fiber lasers have been pumped using commercially available high power/brightness diodes at 790nm and utilize cross-relaxation processes to achieve opticalto-optical efficiencies of 55-65%. However this still generates sizeable thermal distortion at high powers, thus alternative higher efficiency high power 2 ?m fiber laser architectures are still necessary. Both thulium and holmium doped silica fiber lasers can be “in-band” pumped with Tm:fiber lasers operating at ~1.90-1.95 ?m. Similar to ytterbium doped fiber, inband pumping has enabled >90% optical-to-optical efficiency in Tm:fiber lasers. Holmium, on the other hand, generally enables longer wavelength operation with low quantum defect; however, efficiencies <70% are typical in silica fibers. While not entirely understood, it is likely due to non-radiative processes such as phonon interactions or residual OH- absorption. This work utilizes an identical experimental setup to characterize the performance of
Tm:fiber and Ho:fiber oscillators/amplifiers under in-band pumping, directly comparing polarization maintaining thulium-doped step-index fiber (PM
Tm:SIF), non-PM Ho:SIF, and PM Tm:PCF (photonic crystal fiber). The pump and seed sources are wavelength tunable, allowing a wide parameter space for characterization.
9728-29, Session 6
Claude Aguergaray, Patrick Bowen, ALPhANOV (France)
As mid-infrared laser technology improves, the interest to develop high power stable, integrated, reliable fiber laser systems in the 2?m range arises.
So far all-fiber passively mode-locked sources have been demonstrated in the solitonic regime with PM or non-PM fiber and in the stretched pulsed regimes with non-PM fibers. Indeed, net normal cavity lasers capable
9728-31, Session 7
(Invited Paper)
E . Joseph Friebele, Colin C . Baker, Charles G . Askins,
U .S . Naval Research Lab . (United States); John R . Peele,
Sotera Defense Solutions, Inc . (United States); Barbara
A . Marcheschi, Woohong R . Kim, Jas S . Sanghera, U .S .
Naval Research Lab . (United States); Jun Zhang, Radha
K . Pattnaik, Larry D . Merkle, Mark Dubinskii, U .S . Army
44 SPIE Photonics West 2016 · www.spie.org/pw
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Research Lab . (United States)
Erbium-doped fiber lasers (EDFLs) are attractive for directed energy weapons applications because they operate in a wavelength region that is both eye-safer and a window of high atmospheric transmission.
Fabrication of Er-doped fibers (EDFs) is typically done by solution doping where salts of Er and Al (added to reduce Er clustering) are dissolved in a solvent and introduced into porous silica “soot” that is subsequently dried and consolidated to form the fiber core. However, there is no mechanism for controlling the atomic environment of the Er, and in spite of the presence of Al, clustering still occurs. For cladding pumped high energy laser applications it is necessary to have a relatively high Er core absorption because of the relatively low Er absorption cross section and the areal dilution of the pump intensity in the large pump cladding. High
Er concentrations result in the deleterious concentration quenching and cross-relaxation upconversion, which shorten the fluorescence lifetime and decrease laser efficiency.
Nanoparticle (NP) doping is an alternate technique for making EDFs where the local atomic environment of the Er ions is established chemically during
NP synthesis prior to doping. The Er ions are surrounded by a cage of aluminum and oxygen ions, thereby substantially reducing ion-ion energy exchange and its deleterious effects on laser performance. We report the fabrication and measurements of both core and cladding pumped NPdoped EDFs. The optical-to-optical slope efficiency in a resonantly-core pumped MOPA configuration was 80.4%, which compares well with the record efficiency measured on a commercial solution-doped fiber. NP doping has the added benefit of incorporating much less Al in the fiber, e.g., the Al:Er ratio in the NP-doped fiber is only 7 compared to 150 in a comparable solution-doped fiber, but the Er lifetimes are the same.
9728-32, Session 7
Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
(Invited Paper)
Evgeny M . Dianov, Fiber Optics Research Ctr . of the
Russian Academy of Sciences (Russian Federation)
9728-33, Session 7
(Invited Paper)
Valery N . Filippov, Tampere Univ . of Technology (Finland);
Yuri K . Chamorovskii, Konstantin M . Golant, Institute of
Radio Engineering and Electronics (Russian Federation);
Andrei O . Vorotynskii, Oleg G . Okhotnikov, Tampere Univ . of Technology (Finland)
Amplifiers and lasers employed tapered double-clad fiber (T-DCF) as a gain medium exhibit numerous unique advantages compared with regular active fibers. Primarily, T-DCF with large modal size and core diameter at taper end up to 200 µ m could generate nearly ideal beam quality with low non-linear phase shift (B-integral) and is capable of high energy storage. The clad diameter of T-DCF up to 1.6 mm allows pumping by inexpensive powerful low brightness laser diode bars. The axial variation of taper diameter is accompanied by several attractive mechanisms which assist signal propagation. The variation of transverse size of the fiber results in higher pump absorption due to improved clad mode mixing in T-DCF. Tapering of gain fiber also causes an efficient ASE suppression for amplification of low duty cycle pulses. Axially non-uniform geometry of taper increases significantly the SBS threshold for nanosecond pulses amplification.
We have found recently that the threshold of the modal instability of
T-DCF amplifier increases significantly due to small difference between propagation constants of interfering modes.
We have experimentally demonstrated several amplifiers and lasers using ytterbium T-DCF gain fiber. Nanosecond actively Q-switched laser produced
1.6 mJ pulse energy has been used as an efficient pumping source for supercontinuum light generation. The picosecond all-fiber tapered MOPA system with record 300 µ J out-of-fiber pulse energy will be described in details.
For the NIR spectral region from 1150 to 1800 nm, including the ranges from
1250 to 1500 nm and 1600 to 1800 nm where efficient rare-earth fiber lasers are absent, bismuth-doped optical fibers are promising active materials.
The last two spectral ranges are of great interest for some applications, in particular for optical fiber communication. Earlier, we developed Bi-doped fiber lasers and optical amplifiers operating in the first of these spectral ranges. Here, we report new results on the development of bismuth-doped optical fibers and fiber lasers for a spectral range of 1600-1800 nm. A single-mode bismuth-doped germanosilicate fiber (Bi-GSF) containing near
50 mol.% of GeO2 and less than 0.1 mol.% of Bi was drawn from a preform fabricated by the MCVD technique. Intensive luminescence with a maximum at 1700 nm was observed under excitation at 460, 950 and ~1600 nm.
The decay of this luminescence under pumping at 975 nm has a singleexponential shape with the lifetime 500 µ s. The unsaturable losses of the
Bi-GSF at 1568 nm were 0.3 dB/m. The family of Bismuth-doped fiber lasers was realized using the Bi-GSF lengths 15-20 m and an Er-Yb fiber laser operating at 1568 nm as a pump source. The gain bandwidth of the Bi-GSF was 150 nm and this made it possible to obtain CW laser generation in a range of 1625-1775 nm. The output power of the laser at 1700 nm exceeded the watt-level with the slope efficiency 30%. Thus, now bismuth-doped fiber lasers cover the spectral region 1150-1800 nm.
9728-34, Session 8
Deepak Jain, Shaiful Alam, Yongmin Jung, Pranabesh
Barua, Martin M . N . Velazquez, Jayanta K . Sahu, Univ . of
Southampton (United Kingdom)
We demonstrate a 60 µ m core diameter single-trench Yb free Er-La-Al doped fiber having 0.038 ultra-low-NA, fabricated using conventional MCVD process in conjunction with solution doping process. Numerical simulations ensure an effective single mode operation, the effective area varies from
1,820 µ m2 to 1,960 µ m2 for different thicknesses of trenches and resonant rings at 25cm bend radius (including bend-induced distortion). This fiber design can be fabricated with conventional fabrication approaches, which can dramatically reduce the fabrication cost, hence suitable for mass production. Moreover, all solid structure ensures easy cleaving and splicing.
Experimental measurements demonstrate a robust effective single mode operation. Furthermore, this fiber in 4%-4% laser cavity shows a record efficiency of 46% with respect to absorbed pump power at 975nm.
Our study addresses two key issues of power scaling at 1550nm using Erdoped fibers. First, we develop a simple fiber design for mode area scaling at 1550nm, which can be easily fabricated using conventional approaches.
Second we optimize the composition of Er-La-Al during solution doping process to avoid concentration quenching of Er. This optimization leads to high slope efficiency. Further, this fiber owing to its large effective area can be used in MOPA configuration for peak power scaling.
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
9728-35, Session 8
Mateusz Wysmolek, Hakan Sayinc, Laser Zentrum
Hannover e .V . (Germany); Samir Lamrini, Peter Fuhrberg,
LISA Laser Products OHG (Germany); Kristian Lauritsen,
Dietmar Klemme, PicoQuant GmbH (Germany); Uwe
Morgner, Laser Zentrum Hannover eV (Germany) and
Leibniz Univ . Hannover (Germany); Jörg Neumann,
Dietmar Kracht, Laser Zentrum Hannover e .V . (Germany)
High energy nanosecond pulsed laser systems are finding numerous applications in material processing, nonlinear frequency conversion, free space data transmission etc. Arbitrary pulse forming allows for pulse generation tailored to the application or compensation of energy saturation in an amplifier leading to pulse deformation. In our approach we are using a directly modulated semiconductor laser diode emitting at 1950 nm with a PC controlled laser diode driver. The pulse shape is pre-defined by high precision software and can be changed on the fly making an external arbitrary pulse form generator unnecessary. Furthermore, the same software allows for the control of the pulse repetition rate and the generation of pulse bursts making it a promising candidate for material processing. Due to the low output power, the use of 3 fiber amplifier stages is necessary to achieve adequate energies for material processing. With the presented
MOPA system we were able to achieve 30 kW of peak power with clean 10 ns pulses free from spectral and temporal deteriorations. The system is a robust and fully alignment free monolithic fiber setup. An unique feature is a computer controlled seed module with advanced control of pulse shape and repetition rate with burst mode option. To the best of our knowledge this is a first presentation of arbitrary pulse shaping and amplification to 100s µJ pulse energies in Tm3+ doped fibers.
9728-37, Session 8
Robert A . Stegeman, Eric D . Park, Q-Peak, Inc . (United
States)
Tunable Tm-doped fiber laser sources are an attractive solution for chemical detection, medical lasers, and in conjunction with amplifiers, seeding of nonlinear optical processes. Tunability for Tm-doped fiber lasers traditionally comes from an external grating to provide cavity feedback, which has inherent instabilities associated with free-space coupling into and out of a small core optical fiber. This work demonstrates that an all-fiber solution, connected only with the most basic fusion arc splicer, can be made to provide a robust, reliable, and simple tunable 2-um tunable fiber laser source.
The cavity consists of a 793-nm multi-mode laser diode, which is combined with the pass-through signal in a (2+1):1 fused fiber combiner. A piece of 10/130 double clad thulium-doped fiber follows as the gain medium.
An isolator follows the gain fiber to prevent feedback and force a single propagation direction in the ring cavity. A tunable Fabry Perot filter follows the isolator which allows wavelength selection based on the finesse and free-spectral range. A 90/10 fused fiber tap allows 10% of the laser power to exit, while 90% is spliced to the input port of the fused fiber pump/signal combiner.
While operating in CW mode, the laser cavity demonstrates 90-nm of continuous tuning from 1970 – 2060 nm, with optical bandwidths of less than 0.05 nm with greater than 60 dB OSNR. The 90/10 output coupler allows several mW of average power to be emitted.
9728-36, Session 8
Fangzhou Tan, Hongxing Shi, Peng Wang, Jiang Liu, Pu
Wang, Beijing Univ . of Technology (China)
9728-38, Session 8
Benjamin R . Johnson, Daniel Creeden, Julia Limongelli,
Herman Pretorius, Jon F . Blanchard, Scott D . Setzler, BAE
Systems (United States)
We demonstrate on chirped pulse amplification of a dissipative soliton thulium-doped fiber laser. It consists of an all-fiber seed laser, a fiber-based stretcher, two-stage fiber amplifier and free space grating compressor. The oscillator works in the normal dispersion regime and delivers up-chirped pulses with output power of 3 mW at repetition rate of 29.3 MHz. The spectrum of the seed laser is located at 1938 nm with a 10 dB bandwidth of
50 nm. The output pulses is then stretched in ~50 m normal dispersion fiber to 72 ps pulse duration. A single- mode single-clad fiber amplifier is used to amplify the pulse energy to 1.78 nJ. A polarization controller is used after the pre-amplifier to change the polarization of the pulses after passing through a polarization maintaining (PM) isolator. In the main amplifier, a single-mode double-clad polarization maintaining Tm-doped fiber amplifier is used to boost the pulse energy to 229 nJ corresponding to an average power of 6.72
W, with a slope efficiency of 32.7 %. The amplified up-chirped pulses could be dechirped to a duration of 130 fs with energy of 153 nJ.
Most high power Tm-doped fiber lasers operate in the longer wavelength region of the emission spectrum, near 2050nm, where there are minimal re-absorption losses. The 1908nm region in Tm-doped fiber has a high emission cross-section, but it also has significant ground-state absorption, resulting in a higher overall laser threshold and reduced optical efficiency compared to operation at longer wavelengths within the thulium emission band. This three-level operation makes oscillator design critical to laser performance. Operating in the short-wavelength region of the thulium emission band is important for pumping of solid-state and fiber lasers. In this paper, we compare large mode area (LMA) and single-mode (SM) fiber geometries for use in high power 1908nm fiber lasers. With a simple endpumped geometry, we have generated 100W of 1908nm power with LMA fiber at 40% optical efficiency and 117W at 52.2% optical efficiency with a single-mode fiber. We have also power scaled both designs to the >200W power level, showing the capability for further scaling of power in this short wavelength region with high efficiency. In all cases, the fiber lasers are monotlithic, with no free-space coupling.
9728-39, Session 8
Shijie Fu, Tianjin Univ . (China); Wei Shi, Tianjin Univ .
46 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
(China) and Tianjin Institute of Modern Laser & Optics
Technology (China); Jichao Lin, Qiang Fang, Tianjin
Institute of Modern Laser & Optics Technology (China);
Quan Sheng, Haiwei Zhang, Tianjin Univ . (China); Jinwei
Wen, Tianjin Institute of Laser Technology (China);
Jianquan Yao, Tianjin Univ . (China) and Tianjin Institute of
Modern Laser & Optics Technology (China) wavelength soliton can be seen. The pulse width of single-wavelength soliton at 1863 nm is measured to be 3.11 ps and the repetition rate is 2.6
MHz.
The tunability is based on nonlinear polarization evolution (NPE) technique.
The NPE effect induces wavelength-dependent loss in the cavity to effectively alleviate mode competition and enables the multi-wavelength tunable mode locking. The wavelength tuning capabilities can be realized by controlling the polarization in the fiber ring cavity. The system provides a simple and compact solution to tunable multi-wavelength mode locking in fiber lasers. Such tunable laser has potential applications in optical signal processing and communication.
Single frequency fiber laser in 2 ?m regime has attracted intense interest recently due to the great performance in terms of low intensity noise, narrow linewidth and compactness for the applications ranging from coherent LIDAR, high-resolution spectroscopy, to nonlinear frequency conversion. The developed heavily Tm-doped germinate and silicate fibers have facilitated 2 ?m single frequency fiber lasers operating with higher output power and efficiency. However, there are still some limitations on mechanical strength and the compatibility between the active specialty fiber and passive silica fiber in the laser cavity. Fusion splicing between the highly-doped soft glass fiber and silica fiber with low-loss can be well done now, which is still challenging and requires careful handling. In this letter, we report a monolithic, DBR single frequency fiber laser at 1950 nm using a commercial Tm-doped silica fiber.
The maximum output power of the single longitudinal mode laser was
18 mW and slope efficiency versus the launched pump power was 11%.
Single frequency operation was confirmed by the scanning Fabry-Perot interferometer and neither mode hopping nor mode competition was observed as the pump power increased.
The linewidth was measured to increase from 37 to 99 kHz when the pump power rised from 135 to 235 mW. The RIN spectra measured at different pump power showed that it was dominated by a peak at the relaxation oscillation frequency of around 500 kHz and then decreased monotonically towards higher frequencies with the RIN level of around -150 dB/Hz, which approached the shot noise limit.
9728-15, Session PTue
Nan Xia, Seongwoo Yoo, Xuan Wu, Huizi Li, Nanyang
Technological Univ . (Singapore)
Recently, Severe modal degradation was observed in high power, rare earth doped fiber lasers and amplifiers when the pump power was above a power threshold. Many numerical models have been proposed to illustrate the cause of such mode instability, and a good method to suppress the mode instability is of highly important to high power operation area. In this paper, we utilize the beam propagation method (BPM) to numerically simulate the mode instability in a rectangular core fiber with circular cladding shape for the first time. We compare the mode instability between the rectangular core fiber and the conventional circular core fiber. Even in the circular cladding, the rectangular core can dissipate heat more efficiently than the circular core, leading to reduced mode instability. The suppression is more apparent in the high aspect ratio (AR.) rectangular core fiber as the core-cladding boundary gets closer to the edge of the cladding. Utilization of such fiber is a potential way to suppress the modal degradation in high power lasers or amplifiers.
9728-40, Session 8
Zhiyu Yan, Nanyang Technological University (Singapore) and Singapore Institute of Manufacturing Technology
(Singapore); Xiaohui Li, Nanyang Technological Univ .
(Singapore); Biao Sun, Jiaqi Lou, Nanyang Technological
Univ . (Singapore) and Singapore Institute of Manufacturing
Technology (Singapore); Perry Ping SHUM, Nanyang
Technological University (Singapore); Xia YU, Singapore
Institute of Manufacturing Technology (Singapore);
Ying ZHANG, SIMTech, Agency for Science, Technology and Research (Singapore); Qi Jie Wang, Nanyang
Technological Univ . (Singapore)
9728-23, Session PTue
Igor V . Melnikov, National Research Univ . of Electronic
Technology (Russian Federation) and Moscow Institute of Physics and Technology (Russian Federation) and
Univ of Illinois at Urbana-Champaign (United States);
Nikolai Balakleisky, National Research Univ of Electronic
Technology (Russian Federation); Andrey A . Machnev,
National Research Univ . of Electronic Technology (Russian
Federation); J . Gary Eden, Univ . of Illinois at Urbana-
Champaign (United States)
We propose and demonstrate a tunable dual- and tri- wavelength ultra-fast
Tm-doped fiber laser for the first time, and the wavelength tuning range is more than 50 nm, the widest to the best of our knowledge.
The fiber laser is mode-locked by nonlinear polarization evolution (NPE) technique. The setup consists of 1.5-m Tm-doped fiber as the gain medium, two polarization controllers and one isolator to induce the NPE effect, two
793 nm laser diodes with the maximum power of 170 and 200 mW as the pump source, one coupler as the output port, and 70-m single-mode fiber.
By increasing the pump power to 370 mW and either rotating or squeezing the PCs, dual- and tri-wavelength soliton appears. By slightly rotating or squeezing the PCs, multi-wavelength mode locking can be tuned from
1863 to 1915 nm. The fiber laser operates at soliton regime because of the typical Kelly sidebands. The separation between the two wavelengths remains around 10 nm, which is corresponded to the modulation period of cavity transmission. When decreasing the pump power to 310 mW, single-
We report a compact and robust source capable of generating diffractionlimited light ranged from visible- to mid- IR (0.634-?m /1.5 – 1.7-?m / 3.4
– 3.2-?m), using a repetition–switchable single-pass PPLN and BIBO OPO architecture and, a narrow line semiconductor laser. This type of laser which integrates gain chips with a length of fiber that has a Bragg grating (BG) written in its core, has been proven to be a dense and certain source of short picoseconds to nanosecond pulses with peak power sufficient for effective parametric wavelength-tuning applications.
The system is based on a narrow-line 1.064µ m 15-ns MOFA-type system as a pump source, a cw tunable fiber seed laser (1.5 – 1.6µ m), followed by a set of PPLN/BIBO-based OPGs generating pulsed 1.5 – 1.7µ m by
DFG of 1.064µ m, and 0.634µ m by SFG of both 1.5- µ m and 1.064µ m, correspondingly. The laser system delivers nearly diffraction-limited beams both at the visible- and mid-IR tunable wavelengths. The pulse-to-pulse energy instability does not exceed 0.1 %. Optical elements of the scheme
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications can be easily incorporated into the housing with footprint of 500x500x160 mm3.
A variety of the undertaken measures (e.g. optimization of PPLN/BIBO lengths; temperature tuning; spectrum narrowing using the seeder; dimensions minimization, etc.) and technical treatment of the resultant device parameters make it tempting to claim this source to be a universal tool for many applications such as high-resolution spectroscopy, photomedicine, environmental control, etc.
9728-78, Session PTue
Avidan Sharabi, Uzziel Sheintop, Shlomo Y . Goldin,
Jerusalem College of Technology (Israel)
9728-76, Session PTue
Gary Stevens, Thomas H . Legg, Gooch & Housego
(Torquay) Ltd . (United Kingdom)
We present results from an ‘all-fibre’ thulium laser system that can be tuned to any wavelength between 1710 – 2110 nm, without using any moving mechanical parts. An Acousto-Optic Tunable Filter (AOTF) is used as the tuning element, which allows for the wavelength to be tuned in ~ 20 µ s.
Core-pumped and cladding pumped thulium fibres are used to allow for lasing action across the wavelength range.
We use in-house fabricated fused fibre couplers and combiners that have a flattened coupling response with wavelength to allow for the system to be built in ‘all fibre’ design. These couplers have a coupling response that only varies by +/- 10% over the 400 nm operating range.
The laser can output powers between 1-5 mW over 1710 – 2110nm and has a linewidth of <0.2 nm. An Acousto-optic modulator is used as a switch on the output of the laser to switch the signal between core-pumped and claddingpumped amplifier stages. This allows for the output signals to be amplified to ~1W levels.
A new single-mode large-mode-area optical fiber is proposed. The primary part of the cladding is a thin layer with high refractive index. The layer possesses an array of holes drawn in the propagation direction. The array is periodic in the azimuthal direction. The core may be hollow.
The light confinement is achieved via a transmission anti-resonance.
Namely, the array of holes allows coupling between an optical mode inside the primary cladding layer and the light both in the core and in the outer space. The light then sees two channels to penetrate the cladding: direct transmission and holes-assisted transmission. A distractive interference between these channels is achieved at an appropriate combination of fiber parameters.
Computer simulations of the fiber were performed using COMSOL. The open boundary was simulated using a perfectly matched layer and the attenuation constants of different modes were determined via the imaginary parts of their propagation constants.
A fiber holding a single TE01 mode inside a core of 50 µ m radius for the vacuum wavelength 1.55 µ m was designed. The attenuation constant of the
TE01 mode was found to be 5.8e-06 dB/cm] while the other modes had attenuation of at least 4 orders of magnitude larger. These results show the possibility of the realization of a single-mode LMA fiber as long as
7500 meters. The required fabrication tolerances were calculated and the fabrication seemed to be feasible.
9728-77, Session PTue
Jung Hyun Oh, Selee Chang, Sangsoo Oh, Luvantix ADM
Co ., Ltd . (Korea, Republic of); Suk-Youn Y . Suh, Luvantix
SSCP (United States); Ilkwon Oh, Eunje Sung, Luvantix
ADM Co ., Ltd . (Korea, Republic of)
9728-79, Session PTue
Changgeng Ye, Joona J . Koponen, Ossi Kimmelma, Ville
Aallos, nLIGHT Corp ., Lohja (Finland); Timothy S . McComb,
Tyson L . Lowder, nLIGHT Corp . (United States)
The thermal and optical stabilities of optical fiber coatings still remain active areas of research, especially for high-powered fiber laser applications.
The yellowing and mechanical failure of the polymeric fiber coatings at high temperatures have been the limiting factors in the development of high-powered lasers. We have developed new UV-curable fluorinated polysiloxane coatings, which permit higher operational temperatures up to
180C or higher. Fluorinated polymethylsiloxane (PMS), acrylate PMS, and polydimethylsiloxane are copolymerized to form UV-curable low refractive index oligomers. These oligomers have a refractive index from 1.34 to 1.40.
We have observed no visible changes to the optical properties when the cured samples were subjected to 200C for 1,000 hours. The oligomers also have excellent heat resistance. The TGA data revealed less than 5% weight loss at around 300C. We tested our UV-curable fluorinated siloxane high temperature (HT) series coatings against our standard fluorinated urethane
LAP (Luvantix Advanced Process) series coatings. The HT series coatings showed a lower Tg of -40C compared to a Tg of 70C for the LAP series coatings, 80% reduction in yellowness at 250C, and a significantly higher degradation temperature. Fibers coated with the new HT series coatings exhibit thermal and optical robustness at well above 200C.
We report detailed characterization results of Yb-doped Chirally-Coupled-
Core (3CTM) fibers fabricated with nLIGHT’s proprietary Direct Nanoparticle
Deposition (DND) technique. Owing to the DND technique and the strict process control, the doping and refractive index profiles and geometrical tolerances are well managed. Two types of 3CTM fibers with core/ clad geometries of 33/250 µ m and 55/400 µ m and another 25/250 µ m conventional large-mode-area (LMA) fiber are measured and the results are compared in terms of mode field diameter (MFD), modal content, transmission spectrum, etc. The near-field intensity profile is measured by imaging the fiber end onto a CCD camera. The MFD is calculated from the near-field intensity profile. The modal content of the fibers is measured by
Spectrally and Spatially resolved imaging (S2 imaging). The results indicate the 3CTM structure can efficiently filter out all HOMs, making the 3CTM fiber effectively single-moded. The transmission spectra of 3CTM fibers are measured. The feasibility of stimulated Raman scattering (SRS) suppression with 3CTM fibers is demonstrated. A picosecond fiber amplifier is built based on 55/400 µ m 3C fiber, showing robust single-mode operation with peak power >1MW with no sign of SRS.
48 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
9728-80, Session PTue
Enrico Coscelli, Federica Poli, Univ . degli Studi di Parma
(Italy); Romain Dauliat, Univ . de Limoges (France) and
Leibniz Institute of Photonic Technology (Germany) and
XLIM Institut de Recherche (France); Dia Darwich, Univ . de
Limoges (France) and XLIM Institut de Recherche (France) and CNRS (France); Annamaria Cucinotta, Stefano Selleri,
Univ . degli Studi di Parma (Italy); Kay Schuster, Leibniz-
Institut für Photonische Technologien e .V . (Germany);
Aurélien Benoit, Raphael Jamier, Philippe Roy, XLIM
Institut de Recherche (France) to achieve all these requirements we have developed and realized a new fiber design. This fiber is the first polarization maintaining single-mode fiber delivering a flat top intensity. A high quality flat mode was obtained at 1.05
µ m through the use of a well-tailored index profile and single-mode behavior was verified by shifting the injection and using the S? imaging.
Moreover, boron Stress Applying Parts (SAPs) including in the cladding led to a birefringence of 0.6x10-4 and a measured PER better than 20dB even for a long fiber length (~20 m). Alongside the fabrication, we developed a simulation code, using Comsol Multiphysics®, to take into account the stress dependency induced by the SAPs. Further modeling allows us to present an effectively single-mode fiber design, delivering a top-hat mode profile and exhibiting a polarizing behavior.
9728-82, Session PTue
µ
Yanrong Song, Heyang Guoyu, Kexuan Li, Zhiyuan Dou,
Beijing Univ . of Technology (China)
In the last years, the advantages provided by Yb-doped double-cladding
Photonic Crystal Fibers (PCFs), that is very large mode area, strong pump absorption, efficient conversion and robust single-mode regime, have driven a significant development of high power fiber lasers. Currently, thermal effects represent the limit for further power scaling of fiber lasers, since they negatively affect the single-mode behavior of Large Mode Area
(LMA) PCFs. In fact, beyond a certain average power threshold, unwanted energy transfer from the Fundamental Mode (FM) to the Higher-Order
Modes (HOMs), originally weakly guided, occurs, causing a significant beam quality degradation. In this work, the influence of the size and the air-filling fraction of the inner cladding on the first HOM confinement in
Yb-doped LMA PCFs under different heat load values has been investigated with a full-vector modal solver based on the finite element method, used also to solve the steady-state heat equation. In particular, the air-cladding inner dimension and the air-hole diameter in Symmetry-Free PCFs and
Large Pitch Fibers have been modified in order to study which conditions facilitate the coupling between HOM and cladding modes, thus improving the delocalization of the former and making the fiber single-mode behavior more robust. Simulation results have shown that such coupling can be successfully exploited to suppress the HOMs when significant heat load is applied.
Abstract: Some potential applications based on passively mode-locked fiber lasers have been investigated. Recently, more effort has been concentrated on discovering and investigating new and high performance saturable absorbers(SAs) such as topological insulators (TIs), transition mental dichalcogenides (TMDs) which include molybdenum disulfide (MoS2), tungsten disulfide (WS2) and their analogue (tungsten diselenide, WSe2).
Here we demonstrated an all-normal-dispersion Yb-doped mode-locked fiber laser based on tungsten disulphide saturable absorbers (WS2-SA).
The WS2-SA were made by mixing WS2 nanosheets solution with polyvinyl alcohol (PVA), and then evaporated on a substrate. The WS2 nanosheets in the dispersion were observed by an atomic force microscope (AFM). The sizes of the WS2 nanosheets were about 150 to 300 nm and the thickness was about 4.6 nm. The modulation depth of the WS2 film was 1.78% and the saturable optical intensity was 410 MW/cm2, which were measured by a power-dependent absorption system. When the WS2 film was inserted into an Yb-doped fiber laser, the mode-locked pulses were obtained at the wavelength of 1030nm. The pulse width of 2.5 ns and a repetition rate of 2.84 MHz were reached. As the pump power increased to 350 mW, the maximum output power was ~8 mW. To the best of our knowledge, this is the first time to realize mode-locked pulses based on WS2-SA at 1?m waveband. 9728-81, Session PTue
Pierre Gouriou, Lab . de Physique des Lasers, Atomes et Molécules (France) and CEA (France); Florent Scol,
Commissariat à l’Énergie Atomique (France); Benoit
Sevigny, Constance Valentin, Yves Quiquempois, Laurent
Bigot, Rémi Habert, Andy Cassez, Olivier Vanvincq, Lab . de Physique des Lasers, Atomes et Molécules (France);
Emmanuel Hugonnot, Commissariat à l’Énergie Atomique
(France); Géraud Bouwmans, Lab . de Physique des Lasers,
Atomes et Molécules (France)
Compactness, long term stability and no free-space alignment are important advantages of fiber lasers over bulky systems. These fiber lasers have also demonstrated their capability to deliver high-power pulses and are thus suitable for numerous applications. Nevertheless the intensity profile delivered usually has a Gaussian-like shape, which most of the time is sufficient, but it could be interesting, for many applications (laserbiological tissues interactions, heat treatment, industrial laser processing or for seeding large-scale laser facilities like Laser MegaJoule) to obtain a homogeneous intensity profile at the fiber laser output. Moreover several of these applications required a linearly polarized output beam. In order
9728-83, Session PTue
Svetlana S . Aleshkina, Mikhail E . Likhachev, Fiber Optics
Research Ctr . of the Russian Academy of Sciences
(Russian Federation); Denis S . Lipatov, Institute of
Chemistry of High-Purity Substances of the Russian
Academy of Sciences (Russian Federation) and N .I .
Lobachevsky State Univ . of Nizhni Novgorod (Russian
Federation); Oleg I . Medvedkov, Konstantin K . Bobkov,
Mikhail M . Bubnov, Fiber Optics Research Ctr . of the
Russian Academy of Sciences (Russian Federation);
Alexei N . Guryanov, Institute of Chemistry of High-Purity
Substances of the Russian Academy of Sciences (Russian
Federation)
In the present work we demonstrate a novel fiber design for efficient generation and amplification of laser irradiation near the wavelength of
0.98 µ m. The main feature of the fiber design is an extremely low NA
W-type refractive index profile (single-mode at core diameter of 28 µ m) that allowed us to achieve core-to-clad diameters ratio of about 0.31. The
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photodarkening-free silica-based glass matrix was used for fabrication of the Yb-doped core. Square-shaped fibers with dimensions of 28/80x80 µ m, and 40/115x115 µ m coated by low-index polymer (NA=0.46) were fabricated for the laser and amplifier, correspondingly.
The fiber with dimension of 28/80x80 µ m was tested in a simplest all-fiber laser scheme cladding pumped by standard MM laser diode (30W at 915 nm). Output power of 5.5 W at 977 nm (limited by available pump power) was achieved in this configuration. Lasing threshold and slope efficiency were 10 W and 25%, correspondingly.
The fiber with dimension of 40/115x115 µ m was used for building an all-fiber amplifier scheme. The fabricated fiber was spliced with a standard pumpand-signal combiner, seeded by standard semiconductor laser diode with power of 100 mW at 976nm and pumped by two multimode diodes with net power of 60 W. The maximum output power of 5.7 W was achieved. The slope efficiency was about 15%.
9728-84, Session PTue
Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
Migel A . Bello-Jimenez, Erika Hernández-Escobar, Instituto de Investigación en Comunicación Òptica (Mexico);
Evgeny A . Kuzin, Baldemar Ibarra-Escamilla, Manuel
Durán-Sánchez, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico); Antonio Diez Cremades, Jose L .
Cruz, Miguel V . Andrés, Univ . de València (Spain)
Atomes et Molécules (France) and IRCICA (France);
Alexandre Kudlinski, Univ . des Sciences et Technologies de Lille (France) and IRCICA (France); Guillaume Canat,
ONERA (France)
Remote methane concentration measurement using a Differential
Absorption Lidar system can be performed using a single-frequency pulsed laser source at 1645.55 nm. This wavelength cannot be efficiently amplified in conventional Erbium Doped Fiber Amplifier as the gain band stops around 1620 nm.
We report on a single-frequency polarization-maintaining pulsed amplifier at 1645 nm relying on stimulated Raman scattering (SRS) in highly nonlinear silica fibers (HNLF). Considering that SRS converts pump photons to photons frequency-downshifted by 13.2 THz with a gain bandwidth of 2 THz, a 1545 nm pump can efficiently amplify a 1645 nm seed laser. The drawback of using a HNLF is that the single-frequency signal will also experience stimulated Brillouin scattering (SBS) through its amplification.
This issue has been partially solved by designing a two-stage amplification setup minimizing SBS. In the first stage, a 20 m piece of HNLF has been used so that the effective length of the amplified signal stays under SBS threshold. In the second stage, we used a 2.5 m piece of HNLF and high pump peak-power to significantly reduce the effective length, allowing more amplification.
We report on generation of single-frequency 11 µ J energy pulses at 1645 nm corresponding to 150 W peak-power and 80 ns pulse duration at 20 kHz pulse repetition frequency.
A polarization asymmetrical nonlinear optical loop mirror (NOLM) is investigated to perform pedestal-free optical pulses in a figure-eight laser (F8L). The NOLM is composed of a symmetrical coupler, with output ports connected to 220 m of twisted fiber, and a quarter wave retarder
(QWR) located asymmetrically into the loop. In the low-intensity regime the NOLM shows a periodical dependence on the QWR angle, with a minimal and maximal transmission equal to 0 and 0.5, respectively.
The power-dependent transmission is investigated for each circular polarization component at the NOLM output, considering a right circular input polarization, and the dependence on the QWR angle. The results demonstrate that in the low-power regime the NOLM operates as a halfwave plate and the output polarization is orthogonal to the input one.
However, at higher power level the polarization component parallel to the input appears, with a transmission that always begins from zero at low power, allowing the rejection of low-intensity components. This property results very attractive to perform modelocked operation in a F8L. The low-intensity component, with polarization orthogonal to the input, can be implemented to initiate the modelocking process, whereas the parallel component can be associated to high-intensity optical pulses with zero transmission for low-intensity compoments. This configuration allows the generation of optical pulses with peak power close to the maximum peak power value obtainable from the average output power. Experimental results demonstrate that by employing this configuration we can obtain a contrast between the peak and continuous background higher that 30 dB.
9728-85, Session PTue
µ
Philippe Benoit, Nicolas Cézard, Anne Durécu, ONERA
(France); Arnaud Mussot, Lab . de Physique des Lasers,
9728-86, Session PTue
Jeremy Le Dortz, Thales Research & Technology (France);
Marie Antier, Thales Optronique S .A .S . (France); Jérôme
Bourderionnet, Christian Larat, Eric Lallier, Thales Research
& Technology (France); Louis Daniault, Severine Bellanger,
Lab . pour l’Utilisation des Lasers Intenses (France) and
Ecole Polytechnique (France); Christophe Simon-Boisson,
Thales Optronique S .A .S . (France); Jean-Christophe F .
Chanteloup, Ecole Polytechnique (France) and Lab . pour l’Utilisation des Lasers Intenses (France); Arnaud Brignon,
Thales Research & Technology (France)
Coherent beam combining (CBC) of fiber amplifiers provides an attractive mean of reaching high peak and high average powers. Active CBC techniques involve phase detection and compensation of the phase variations of each amplifier. Interferometric phase measurement has proven to be particularly well suited to phase-lock a large number of fibers in continuous regime. In this presentation, we demonstrate for the first time the phase locking of three fibers in femtosecond pulse regime with this technique.
A master oscillator generates pulses of 300fs (chirped at 200ps). The beam is split into four channels. Phase locking is implemented on three fibers with respect to the fourth, acting as a phase reference. Prior to phase locking, the optical path differences are adjusted. Interferograms for the three fibers are recorded at 1kHz with a camera. A dedicated algorithm is developed to measure both the phase and the delay between the fibers. The delay and phase shift are thus calculated collectively from a single image and piezoelectric fiber stretchers are controlled in order to ensure compensation of time-varying phase and delay variations. The measured phase shift errors between the fibers are below ?/80rms when the servo-loop is operating.
Phase noise power spectral densities of a fiber amplifier operating in the short pulse regime will be also presented in opened and closed loop to assess the bandwidth of the control loop and the capability of our locking technique to perform CBC of fiber amplifiers operating in the short pulse regime.
50 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
9728-87, Session PTue
Michael Steinke, Jörg Neumann, Dietmar Kracht, Peter
Wessels, Laser Zentrum Hannover e .V . (Germany)
A novel statistical model for the energy transfer process in Er3+:Yb3+codoped glasses, e.g. fibers, is presented. The model is based on an existing stochastic model for the homogeneous up-conversion in Er3+-doped glasses and the most important advantage is the correct modeling of the energy transfer as a dipole-dipole interaction. Thus, the model avoids the unreasonable but common modeling of the Er3+-to-Yb3+ energy transfer as a fixed rate which is simply multiplied with the upper Yb3+ state population and the ground state Er3+ population. Exemplary results obtained with the novel statistical model behave reasonable, i.e. the population densities of the Yb3+ and Er3+ upper states depend on the individual parameters of the model as expected. Therefore, the presented model provides good prospects to study optimization strategies of Er3+:Yb3+-codoped fibers.
Furthermore, the model can be further developed and expanded in the future, e.g. by including energy migration amongst the individual Yb3+-ions and Er3+-ions.
Major advantages over traditional methods for these applications can be achieved with dual-comb technique. For example, dual-comb spectroscopy provides orders of magnitude improvement in acquisition speed over standard Fourier-transform spectroscopy while still preserving the high resolution capability. Wider adoption of the technique has, however, been hindered by the need for complex and expensive ultrafast laser systems.
Here, we present a simple and robust dual-comb technique that employs a free-running bidirectionally mode-locked fiber laser operating at telecommunication wavelength. Two femtosecond frequency combs (with a small difference in repetition rates) are generated from a single laser cavity to ensure mutual coherent properties and common noise cancellation. We demonstrate real-time absorption spectroscopy measurements without the need for complex servo locking or adaptive sampling with accurate frequency referencing and relatively high signal-to-noise ratio. The compact and all-fiber implementation scheme makes this technique a promising tool for practical, outside-of-laboratory applications.
9728-90, Session PTue
Xiaohui Fang, Beijing Univ . of Technology (China)
9728-88, Session PTue
Manuel Durán-Sánchez, Instituto Nacional de Astrofísica,
Óptica y Electrónica (Mexico) and Cátedras CONACyT
(Mexico); Ricardo I . Álvarez-Tamayo, Univ . Tecnológica de Puebla (Mexico); Olivier J . M . Pottiez, Ctr . de
Investigaciones en Óptica, A .C . (Mexico); Berenice Posada-
Ramírez, Baldemar Ibarra-Escamilla, Evgeny A . Kuzin,
Instituto Nacional de Astrofísica, Óptica y Electrónica
(Mexico); Antonio Barcelata-Pinzón, Univ . Tecnológica de
Puebla (Mexico)
The effect of fiber length on ultrafast pulse formation in active dual-core fiber laser is investigated numerically, which has been ignored in previews studies. The simulation results show that stable self-starting mode-locked operation can be realized with a dual-core fiber length shorter than the linear coupling length. A filter is necessary to stabilize mode-locking operation when the fiber length is longer than the linear coupling length.
And mode-locking operation can not be self-started from noise with a fiber length equal to the linear coupling length.
9728-91, Session PTue
George A . Adib, Yasser M . Sabry, Diaa A . Khalil, Ain Shams
Univ . (Egypt)
We present experimental results of a proposed dual wavelength fiber laser with Er/Yb double clad fiber. With pump power variations the laser to 1 W
Self-Q-switched pulses are obtained. With a pump power range from 1 W to 2 W, self-pulsing operation is observed. With pump power above 2 W
CW operation is achieved. The linear cavity laser is based in the use of two fiber Bragg gratings for wavelength selection and a Sagnac interferometer for cavity losses adjustment to obtain dual-wavelength operation. Power efficiency is around 36%. In self-Q-switch operation maximal repetition rate is 60kHz with pulse duration in micro seconds range. With pump power of 10 W, the maximal average output power of 3.6 W is obtained for CW operation.
9728-89, Session PTue
Khanh Q . Kieu, Seyed Soroush Mehravar, Robert A .
Norwood, Nasser N . Peyghambarian, College of Optical
Sciences, The Univ . of Arizona (United States)
Dual-comb technique has enabled exciting applications in high resolution optical spectroscopy, precision distance measurements, and 3D imaging.
Optical fiber cavities are basic building blocks in different applications including fiber laser, fiber-laser frequency combs,swept laser source, environmental and rotation sensors. For many applications, the cavity length is needed to be relatively long- in the order of meters or kilometers- to achieve a fine 3-dB bandwidth and free spectral range stability.
The characterization of long fiber cavities is, thus, essential to design these systems and predict their practical performance.The conventional techniques for optical cavity characterization are not suitable for long fiber cavities due to the cavities’ small free spectral ranges and due to the wavelength instability (length variations) caused by the environmental effects.In this work, we present a novel technique to characterize long fiber cavities using multi-longitudinal mode fiber laser source and RF spectrum analyzer. The output of the laser is used as an input to the cavity under test. The output of the cavity is fed to a square-law optical detector and its electrical output is recorded on the RF spectrum analyzer. Then, the RF spectrum is used to obtain the response of the cavity. The method has been applied experimentally to characterize ring cavities with lengths of 6 m and
2.4 km. The fiber laser source is formed in a ring configuration, where the fiber laser cavity length is chosen to be 15 km to ensure the free spectral range is much smaller than the free spectral range of the characterized passive fiber cavities. The results are compared to theoretical predictions with very good agreement.
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9728-92, Session PTue
Manuel Ryser, Alexander M . Heidt, Thomas Feurer, Valerio
Romano, Univ . Bern (Switzerland)
We have demonstrated a fiber ring oscillator in modelocking, Q-switching and simultaneous Q- switched modelocking operation mode at constant pump power level. The different oscillation states of the cavity were reached by varying the mode-field area within the graphene oxide saturable absorber (GO-SA) and not as commonly done by adjusting the optical pump power. All fibers and fiber coupled elements used in our setup are polarization maintaining. Thus, the only available mode-locking mechanism in this fiber ring oscillator is the saturable aborption at the GO-SA and mode-locking based on nonlinear polarization rotation can be excluded.
Widely used methods for producing ultrashort pulses in laser cavities are Q- switching and modelocking. Q-switching allows the generation of milli-joule pulses with microsecond to nanosecond duration and hertz to many kilohertz repetition rates. Mode-locking produces typically picojoule to nano-joule pulses with femto- to picosecond pulse durations and megahertz to gigahertz repetition rates. Furthermore, a laser cavity can also operate simultaneously in Q-switched and modelocking regime to produce a pulse train at MHz with a modulation envelope at kHz repetition rate. The Q-switched modelocked pulses are modulated in amplitude the most intense pulses can reach energies several times higher than would be possible with pure modelocking.
With the approach presented here various operation modes can be achieved at the same pump power level, which gives great flexibility in generating ultrashort optical pulses over a broad range of durations, repetition rates and energies from the same laser cavity.
9728-93, Session PTue
Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
Sergey M . Kobtsev, Aleksey V . Ivanenko, Yurii Fedotov,
Sergey V . Smirnov, Novosibirsk State Univ . (Russian
Federation); Artur Golubtsov, Sergey Khripunov,
Novosibirsk State Univ (Russian Federation)
9728-94, Session PTue
Maksim Y . Koptev, Institute of Applied Physics of the
RAS (Russian Federation); Elena A . Anashkina, Institute of Applied Physics of the RAS (Russian Federation) and N .I . Lobachevsky State Univ . of Nizhni Novgorod
(Russian Federation); Alexey V . Andrianov, Institute of
Applied Physics of the RAS (Russian Federation); Vitaly V .
Dorofeev, Institute of Chemistry of High-Purity Substances of the Russian Academy of Sciences (Russian Federation);
Alexey F . Kosolapov, Fiber Optics Research Ctr . of the
Russian Academy of Sciences (Russian Federation);
Sergey V . Muravyev, Institute of Applied Physics of the
RAS (Russian Federation); Arkady V . Kim, Institute of
Applied Physics of the RAS (Russian Federation) and N .I .
Lobachevsky State Univ . of Nizhni Novgorod (Russian
Federation)
We propose a widely tunable in the 1.6-2.6 ?m range femtosecond fiber laser source, generating high-quality sech-shaped pulses with the duration of the order of 100 fs. The source contains an all-fiber hybrid Er/
Tm femtosecond laser system that generates 2 nJ 150 fs pulses in Erbium channel and 4 nJ 125 fs pulses in Thulium channel. The laser was coupled to a piece of suspended-core microstructured TeO2-WO3-La2O3 glass fiber with 3.2 ?m core diameter and ZDW of approximately 1.5 ?m. We experimentally obtained tunable high-quality Raman solitons up to 2.25 and
2.6 ?m with the pump at 1.6 and 2 ?m, respectively. Their spectral widths correspond to the Fourier transform-limited duration of about 100 fs. We have also made theoretical studies of self-frequency soliton shifting in the tellurite fiber with carefully measured and calculated parameters, based on the one-way wave equation dealing with the full electric field of light. Our numerical model is in a very good agreement with the experiment and also shows Raman soliton self-frequency shift in the range well beyond 3 ?m for increased pump energy. So, the demonstrated turnkey fiber-based laser source can be used for applications requiring high-quality ultrabroadband femtosecond optical pulses.
For the first time a method for switching between generation of single- and double-scale pulses has been demonstrated in a mode-locked figureeight NALM-based all-PM-fibre Yb master oscillator by adjustment of two pumps power. Introduction into a F8 configuration of a non-linear amplifying loop mirror with two active media not only ensured relatively high average output power of the master oscillator (> 0.5 W at 22-MHz repetition rate), but also allowed switching laser operation from one pulse type (single-scale coherent pulses with duration of < 10 ps) to another - femtosecond clusters with envelope width of 16 ps and sub-pulse duration
< 200 fs. Implementation of an all-PM-fibre configuration dispensed with the requirement of polarisation controllers (they were used in the previous configuration of this master oscillator) and to trigger mode-locked operation by selection of power levels of the two pump sources. The suggested optical layout features output via two ports. A larger portion of the radiation exited the master oscillator through port 1 at the average output power of 600 mW for single-scale pulses and 525 mW for femtosecond clusters
(double-scale pulses). The average power of radiation exiting through port
2 amounted to 140 and 280 mW correspondingly. The proposed method of switching between generation of single-scale and double-scale pulses by adjustment of relative levels of two pump sources provides considerably faster and more reproducible regime switching in comparison to switching by adjustment of polarisation controllers.
9728-95, Session PTue
Ryutarou Yamashita, Kazuo Maeda, Goro Watanabe,
Kazuyoku Tei, Shigeru Yamaguchi, Tokai Univ . (Japan); Jun
Enokidani, Shin Sumida, OPT-i Co ., Ltd (Japan)
We report on tunable pulse width and energetic pulse generation from a nonlinearly compressed monolithic fiber MOPA system. The master seed source employs a Mach-Zehnder intensity modulator (MZIM). This seed source has operational flexibility with respect to pulse width, 90 ps to 2 ns and repetition rate, 200 kHz to 2 MHz. The seed pulses are amplified by a monolithic three-stage amplifier system based on polarization maintain
Yb-doped fibers. The maximum output power was 32 W at the shortest pulse condition, the pulse width of 90 ps and repetition rate of 2 MHz. A spectral width after amplification was broadened to 0.65 nm at RMS width.
Both of ASE and SRS are not observed in the spectrum. After amplification, we also demonstrated pulse compression with a small piece of chirpedvolume-bragg-grating (CVBG) which has the dispersion rate of 81 ps/nm. As a result of pulse compression, the shortest pulse width was reduced from
52 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
90 ps to 4 ps, which brought an increase of the peak power up to 2.9 MW.
The autocorrelation traces are well matched with the Gaussian function. The compressed pulses are clean with very little structure in there wings. We can expand the operation range of the monolithic-fiber MOPA system in pulse width, 4 ps to 2 ns.
9728-96, Session PTue
Sergey L . Semjonov, Olga N . Egorova, Oleg I . Medvedkov,
Maxim S . Astapovich, Andrey G . Okhrimchuk, Evgeny M .
Dianov, Fiber Optics Research Ctr . of the Russian Academy of Sciences (Russian Federation); Boris I . Denker, Boris
I . Galagan, A . M . Prokhorov General Physics Institute of the Russian Academy of Sciences (Russian Federation);
Sergey E . Sverchkov, A . M . Prokhorov General Physics
Institute (Russian Federation)
25, 16302 (2007)]. Using numerical simulation the solitons collision and merge of solitons in dispersion oscillating fiber are considered. Rogue wave arises as result of the inelastic collision of optical solitons. Inelastic collisions are forced by periodical variation of the fiber dispersion. Due to inelastic interactions, the solitons merge together and give birth to a new soliton whose amplitude is significantly greater than the amplitude of the other satellite solitons. After the merging process, the dynamics of the output pulse is determined mainly by a single high-amplitude soliton called as rogue wave. The parameters of the rogue wave depends on the modulation period of the fiber diameter, repetition rate of the host laser. The generation of single high-amplitude soliton can be actively controlled via chirp of input pulses. The generation of the rogue waves both in active and passive dispersion oscillating fibers is considered.
9728-98, Session PTue
Soichi Kobayashi, Mikoto Takahashi, Mizuki Ohara, Ikki
Kondo, Chitose Institute of Science and Technology
(Japan); Yusuke Fujii, Photonic Science Technology, Inc .
(Japan)
Phosphate glass is a unique host for lanthanide ion doping: high concentrations of rare earth (RE) ions can be incorporated into phosphate glass, the phosphate glass host provides efficient and irreversible energy transfer from Yb3+ ions to Er3+. Additionally, Yb-doped phosphate glass is highly resistant against photodarkening even at high Yb3+ concentration.
High doping levels of phosphate fibers make it possible to obtain high gain and high output power per unit length, thus reducing the length of active fibers in comparison to silica based fibers.
A substantial drawback of the use of phosphate glasses as a material for fiber fabrication in comparison with silica is their low stability; exposure to air moisture causes degradation of the phosphate fibers over time.
Moreover, due to the sharp difference in their physical properties, splicing of phosphate and silica fibers is difficult.
In this presentation, we describe composite optical fibers with rare-earth co-doped phosphate-glass core in a silica-glass cladding. High RE-ion concentrations in the phosphate core of the composite fiber allow fiber length reduction in comparison with silica fibers. The silica cladding provides high mechanical strength and protects the phosphate core from air moisture while making it easier to splice with silica fibers. Both fabrication of fibers and their optical properties will be discussed. The lasing efficiency of the composite fibers was found to be high in both cases - cladding and core pumping.
1.3 - 1.55 ?m optical amplifiers for the long distance up-stream and down-stream networks for a future increase of fiber access network in telecommunications are attractive. A bismuth-doped silica glass has a potential of the broadband spectrum as laser and amplifier applications at
1.3 -1.55 ?m. The bismuth-doped fiber lasers and amplifiers were discussed by the Dianov group fabricating by the MOCVD method. In this report optical amplification characteristics at 1.3 - 1.55 ?m are presented with the water free hexagonal double-clad bismuth-doped silica fiber (HDC-BDF) made by the VAD method. The bismuth and aluminum ions were vapor–
?phase doped into the silicon and germanium oxide. The concentration of
Bi oxide in the core glass was measured as 0.8 wt% by EDX spectroscopy.
Refractive index difference between the core and the first cladding in the preform was measured as 0.5 % by the optical fiber preform analyzer.
The hexagonal preform was drawn into the fiber where the core and the first cladding diameters were measured as 7 ?m and 100 ?m between flat surfaces, respectively. The relative refractive index difference between the silica first-cladding and the polymer first-cladding is 3.6%. Pumping into the
HDC-BDF was performed by using the 15 degree tilt-polished fiber from the hexagonal surface with the multimode fiber pigtail of the pumping LD. In the case of the hexagonal fiber it is easy to realize a perfect splicing with the single-mode fiber. 1 dB/m amplification in 1310 nm was measured with 4 m long HDC-BDF where SNR is over 35 dB with -40 dBm input signal.
9728-97, Session PTue
Alexey Sysoliatin, Konstantin Gochelashvili, A . M .
Prokhorov General Physics Institute of the Russian
Academy of Sciences (Russian Federation); Andrey
I . Konyukhov, N .G . Chernyshevsky Saratov State Univ .
(Russian Federation); Leonid A . Melnikov, Saratov State
Technical Univ . (Russian Federation); Mikhail Y . Salganskii,
Institute of Chemistry of High-Purity Substances of the
Russian Academy of Sciences (Russian Federation)
Generation of high-intensity rogue waves from optical turbulence or breathers is considered usually as statistically-rare process [J.M. Dudley et al. Nature Photonics 8, 755 (2014)]. We propose a new approach for the generation of separated optical rogue waves “on demand”. The proposed scheme utilizes dispersion oscillating fiber. Variation of the fiber dispersion can be made during its drawing process [A.A. Sysoliatin et al. Opt. Expr.
9728-99, Session PTue
S . Arun, Ctr . for Nano Science and Engineering (CeNSE)
(India) and Indian Institute of Science (India); Balaswamy
Velpula, Indian Institute of Science (India) and Ctr . for
Nano Science and Engineering (India); Great Chayran,
Indian Institute of Science (India); P . Vanitha, Abhishek
Kumar, V . R . Supradeepa, Indian Institute of Science (India) and Ctr . for Nano Science and Engineering (India)
An essential requirement in lasers and amplifiers utilizing a rare-earth doped gain medium is to have substantial match between the emission wavelengths of the pump laser diodes to the absorption band of the gain medium. This would enable the optimal balance of laser efficiency
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications and nonlinearity. Further, this leads to improved system reliability - by minimizing issues arising from unabsorbed pump and cost - by minimizing the length of gain media. However, the emission wavelengths vary as a function of various parameters, primarily output power (drive current), temperature and variation in device parameters. The latter two factors can be easily overcome through the choice of proper heat-sink temperatures and by using diodes binned according to their emission wavelength.
However, a fundamental limitation is the variation of emission wavelength as a function of output power (drive current). Currently, the alternative is to use wavelength locked laser diodes. This comes at the cost of reduced efficiency and/or enhanced price owing to additional components and packaging necessary in each module.
In this work, we demonstrate a novel drive scheme for standard laser diode modules without wavelength locking. This scheme enables “alwaysresonant” pumping by the diodes. The deleterious effect of emission wavelength drift accompanying power tuning, is completely avoided. In this work, we demonstrate the drive mechanism and its performance in a fiber amplifier configuration. We anticipate this scheme to have significant impact in enabling a cost-effective solution which achieves an optimal balance of efficiency, nonlinearity and reliability in laser systems.
electrically tunable all-fiber graphene device with high efficiency based on strongly enhanced graphene-evanescent wave interaction. We successfully fabricated a graphene-based field effect transistor on a side-polished fiber mediated by an ion-liquid. Gate-variable electrical transport and related optical properties are simultaneously studied as a function of number of graphene sheet, which reveals that it exhibits non-resonant large optical transition change (> 90%) for applied voltage of less than 3 V. Taking the advantages of all-fiber device with high optical damage threshold, the proposed device is successfully integrated into all-fiber laser system as an electrically tunable in-line graphene saturable absorber. We observed that nonlinear saturable absorption properties of our all-fiber graphene device can be tuned as we adjust the applied electrical signal. This subsequently modifies the laser cavity condition, enabling gate-controlled pulsed fiber laser operation at various operation regimes including continuous wave mode-locking and Q-switching. Further possible applications of the proposed device for tunable nonlinear optic signal generation, fine control of passively mode-locked fiber laser, and broadband optoelectronic devices will be also discussed based on our all-fiber graphene devices with enhanced device efficiency.
9728-100, Session PTue
Nishant K . Shekhar, Sourav Das Chowdhury, Ranjan Sen,
Mrinmay Pal, Central Glass and Ceramic Research Institute
(India)
9728-102, Session PTue
Jing Wang, Yubin Hou, Qian Zhang, Dongchen Jin, Ruoyu
Sun, Hongxing Shi, Jiang Liu, Pu Wang, Beijing Univ . of
Technology (China)
In the process of development of high energy nanosecond pulsed fiber lasers, we confronted a phenomenon that manifested itself as an intensity limiter much like the non-linear scatterings, namely SBS and SRS. The phenomenon was coined ‘Gain Saturation’ in laser literature, notorious for its distorting ability of square shaped pulses. But its intensity limiting behavior was accentuated only when a 100ns width Gaussian pulse was unable to get amplified over 2 KW of peak power. Higher pumping only led to broadening of the pulse to 120ns without enhancement of its peak power. A numerical simulation was done so as to mimic the occurrence of gain saturation. Initially the numerical model predicted a higher intensity achievable than what was measured in the experiment. This mismatch of numerical prediction and experimental observation was later corrected by incorporating the effect of ‘Numerical Aperture’ of the fiber. The numerical simulation combined with experimental observation led to an empirical relation between fiber parameters, fiber material and the maximum intensity that could be achieved for a Gaussian pulse of constant width before gain saturation appeared. Based on the empirical relational, a fiber with required dimension was fabricated which later in a table top experiment attained the desired peak power combined with high energy. Simultaneously, a fluid analogy was also devised in order to explain in an alternate way the happening of ‘Gain Saturation’. The fluid analogy also helped in simplifying the complexities of “Gain Saturation’.
We have demonstrated a high power, high-optical signal-to-noise ratio
(OSNR) single-frequency 1 ?m Brillouin all-fiber laser. The Brillouin fiber laser (BFL) consists of a continuous-wave Yb-doped single-frequency seed source, one-stage Yb-doped fiber amplifier (YDFA) pumped by fiberpigtailed multimode laser diode and a single-pass Brillouin ring cavity. The seed source is a homemade short-linear-cavity distributed Bragg reflector
(DBR) single-frequency fiber laser with the output power of 35 mW and the linewidth of 20 kHz. Through one-stage YDFA, the seed laser is amplified to
2.615 W limited by the optical power of the isolator. The laser is then split into two unequal parts with 99/1 fiber coupler and the output from 99% coupler is served as the Brillouin pump (BP) with 2.588 W output power, which is injected into the single-pass Brillouin ring cavity. By optimizing the length of the cavity to 10m, stable single-longitudinal-mode operation is obtained with 2 kHz linewidth owing to the linewidth narrowing effect.
The single-frequency BFL generates an average output power of 1.402 W at 2.588 W pump power with 70% output coupler. The laser does not show any phenomena of saturation, so more output power is expected if a higher power pump laser is launched. The slope efficiency is 79% considering the loss of the circulator. The OSNR of the BFL in the maximum output power is 77 dB which can be 27 dB better than the BP owing to the intensity and phase-noise reduction of the SBS process.
9728-101, Session PTue
Dong-Il Yeom, Ajou Univ . (Korea, Republic of)
Active control of light in an optical fiber has been studied with great interest due to its compatibility with diverse fiber-optic communication and fiber laser systems. Although the optical absorption properties of graphene can be modified through the Fermi-level control in a graphene layer by applied electrical signal, realization of gate-controlled graphene device in an optical fiber platform remains highly challenging. In this presentation, we report an
9728-103, Session PTue
Vincent Roy, Claude Paré, Pierre Laperle, Louis Desbiens,
Yves Taillon, INO (Canada)
Large mode area (LMA) fibers with depressed-index cladding layer and confinement of rare-earth dopants can provide effective suppression of high-order modes (HOMs). The latter favors preferential amplification of the fundamental mode through optimized differential in mode overlap with rare-earth dopants whereas the former results in increased differential bending losses as a result of the lower effective numerical aperture seen by HOMs. Both of these methods are shown herein to be quite effective at
54 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications suppressing HOMs for fibers with large core diameters when implemented together. A polarization-maintaining Yb-doped double-clad fiber with
35/250 µ m core/clad diameter has been fabricated from conventional MCVD and solution doping process according to this design. The fiber which has an effective fundamental mode area close to 500 µ m2 yields near diffractionlimited output with beam quality factor M2 close to 1.1 when tested as a power amplifier with a 1064 nm coherent seed light source. The exceptional beam quality is maintained for high power, well over 20dB of gain. Beam pointing measurements provide additional evidence for near single-mode behavior as the pointing fluctuations are shown to be negligible. Besides, the beam characteristics are further examined for coupling conditions that yield a significant fraction of energy into HOMs in order to show how effective is the suppression of these modes. We are confident for the effective mode area of the LMA fiber design proposed herein to be readily scalable over 1000 µ m2 and yet allow for reasonably good beam quality.
provided an error signal for active phase stabilization which was performed via Locking of Optical Coherence by Single-Detector Electronic-Frequency
Tagging (LOCSET).After phase stabilization, the beams were coherently combined via the 1x5 DOE. A total combined output power of 5 kW was achieved with 82% combining efficiency. The intrinsic DOE splitter loss was
5%. Similarly, the losses due to non-ideal polarization extinction were 2.5%.
Other losses include residual phase error control (1-2%), amplifier amplified spontaneous emission (ASE), and largely, fractional beam displacement and misalignment errors. Near diffraction-limited beam quality at 5 kW was attained with a measured M2 value of 1.06.
9728-106, Session PTue
Haiwei Zhang, Wei Shi, Quan Sheng, Tianjin Univ . (China)
9728-104, Session PTue
Oleg Shatrovoy, Boston Univ . (United States); Siddharth
Ramachandran, Lars Rishoj, The Boston Univ . Photonics
Ctr . (United States)
We analyse the linewidth characteristic of a high-power single-frequency
Tm-doped fiber amplifier (TDFA) with the power up to 45 W for the first time. The Lorentzian line shape 3dB linewidth of the output signal is ~56 kHz at the maximum power. Moreover, the linewidth of the output laser with different power is measured via the delayed self-heterodyne method. The experimental results indicate that the Lorentzian line shape linewidth decreases firstly and then increases later with the increase of output signal power. It shows that the Lorentzian linewidth of high-power single-frequency TDFA increases with the increment of the amplifier gain factor. However, with the increase of pump power, the broadening of the laser linewidth is due to the increase of the in-band amplified stimulated emission, which can reduce the amplifier gain factor.
We present a simulated device that performs efficient (90%) secondharmonic generation (SHG) of a truncated Bessel beam that mirrors higher order modes (HOM) of fibers, while simultaneously converting it to a
Gaussian-like spatial profile. The simulations reveal that a 1064-nm 250-W truncated Bessel beam with 9 rings, mirroring the profile of an LP0,10 mode, under noncollinear phase matching conditions, converts into a 225-W beam with primarily a central spot. The central spot has 93% of its power within a 5mrad divergence angle and a 70% overlap with a perfect Gaussian beam. The simulated results reveal two attractive features – the feasibility of efficiently converting HOMs of fibers into Gaussian-like beams, and the ability to simultaneously perform frequency conversion, which may have applications in realizing high-power sources in non-traditional colors.
The split-step method was used to alternatingly apply the solutions of the linear and nonlinear parts of the differential equations describing the second-harmonic interaction with diffraction over a small propagation steps.
Beam input power and phase mismatch for optimal output were chosen by performing a parameter sweep of those variables.
9728-105, Session PTue
Angel Flores, Air Force Research Lab . (United States);
Thomas Ehrehreich, Roger H . Holten, Leidos, Inc . (United
States); Iyad Dajani, Air Force Research Lab . (United
States)
Recently, we have shown that assuming an optimal pattern is chosen, pseudo-random bit sequence (PRBS) phase modulation provides superior
SBS suppression to that provided by white noise source (WNS) for a given fiber length and signal linewidth. Furthermore, we successfully demonstrated coherent beam combining (CBC) of two 150W PRBS phase modulated fiber amplifiers. In this work, we demonstrate CBC of five path length-matched 1.2 kW fiber amplifiers with a diffractive optical element (DOE) and report a combined output power of 5 kW. Each non polarization-maintaining fiber amplifier provides approximately 1.2-1.3 kW of near diffraction-limited output power (M2~1.1). A low power sample of each laser was utilized for active polarization control. After polarization locking, polarization extinction ratios (PER) of 15-16 dB were measured for each amplifier. A low power sample of the combined beam after the DOE
9728-107, Session PTue
µ
Jan Tarka, Jakub Boguslawski, Maciej Kowalczyk, Grzegorz
J . Sobon, Jaroslaw Z . Sotor, Wroclaw Univ . of Technology
(Poland)
We demonstrate the usage of a new saturable absorber material -antimony telluride (Sb2Te3) for efficient mode-locking of an Thulium-doped fiber laser. The Sb2Te3 layers were obtained by mechanical exfoliation and transferred onto the fiber ferrule. The all-fiber laser was capable of generating optical solitons with the full width at half maximum of 4.5 nm centered at 1945 nm, with 39.5 MHz repetition rate and more than 60 dB signal to noise ratio. The pulse energy of the generated 850 fs pulses was at the level of 30 pJ.
9728-109, Session PTue
Xiaosheng Huang, Seongwoo Yoo, Ken Tye Yong, Nanyang
Technological Univ . (Singapore); Feng Luan, Shenzhen
University (China); Wenliang Qi, Daryl Ho, Nanyang
Technological Univ . (Singapore)
An improved design for hollow-core inhibited coupling fibres (HC-ICFs) is presented. It consists of eliminating asymmetric part of the core-cladding boundary of a hollow inhibited coupling fibre and has a fibre structure with split cladding (SCF). The SCF has desirable properties such as a symmetric and discontinuous core-cladding boundary which help to reduce the structure deformation in fabrication process. In addition, the discontinuous core-cladding boundary can avoid the high loss introduced by
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the touching areas between capillaries. The negative curvature also can be easily achieved in this fibre design even without the pressure control during fabrication process.
Simulation results are presented to compare the confinement loss of : conventional hollow inhibited coupling fibre (HIF) and SCF. Overall the leakage losses of HIF and SCF are in the same level and both have the potential to have lower background loss than the telecom fibres. However, the structure like HIF is more likely to suffer a core shape deformation since its core-cladding boundary is asymmetric and continuous.
The relationship between confinement loss and tube pitch amplification coefficient, g, has been studied and a confinement loss lower than 0.01dB/ km can be achieved by controlling the pitch amplification coefficient. The fabricated SCF shows promising results with insignificant deformation, and the measured transmission is consistent with the simulation result.
9728-110, Session PTue
Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
Huizi Li, Seongwoo Yoo, Sidharthan Raghuraman, Daryl
Ho, Xuan Wu, Tianye Huang, Nanyang Technological Univ .
(Singapore) couplers.
The novel wavelength swept laser source will offer high stable and narrowlinewidth, which especially benefits for image depth and image stability for optical coherence tomography (OCT) and high sensitivity for optical sensor
9728-112, Session PTue
Minwan Jung, Korea Institute of Science and Technology
(Korea, Republic of) and Univ of Seoul (Korea, Republic of); Junsu Lee, The Univ . of Seoul (Korea, Republic of);
Wongeun Song, Advanced Photonics Research Institute
(Korea, Republic of) and The Univ . of Seoul (Korea,
Republic of); Ju Han Lee, The Univ . of Seoul (Korea,
Republic of); Woojin Shin, Gwangju Institute of Science and Technology (Korea, Republic of)
A photodarkening (PD) effect in ytterbium (Yb)-doped fiber is dependent on the number of excited ions in the upper level of Yb ion. However, the dependence of pumping wavelengths has been overlooked. In our work, we show that the PD is not only dependent of the population inversion level but also the pump wavelength. We use different wavelengths (918nm and
980nm) to core-pump a Yb:Al fiber to measure the PD. The inversion levels are kept at same values at both pumping wavelengths. The PD is assessed by temporal transmitted power decay at 620 nm as a probe beam, and transmission spectra change after the PD. The results reveal that under the same inversion level, 980 nm pumping can lead to more significant photodarkening effect than 918 nm counterpart. In addition, the 980 nm pumping wavelength induce stronger UV emission, which might suggest the
UV emission is related to the creation of the PD. Our results indicates that using 918 nm pumping source would be helpful to reduce the PD.
9728-111, Session PTue
Gahee Han, Nam-Su Park, Chang-Hyun Park, Chang-Seok
Kim, Pusan National Univ . (Korea, Republic of)
High peak power ~2 ?m pulse lasers are practically useful in numerous applications, such as eye-safe LIDAR, medicine, spectroscopy, remote sensing and mid-infrared (IR) generation. Especially, optical fiber lasers exhibit a range of advantages over their bulk optics-based counterparts in terms of beam quality, reliability, and environmental stability. The mode-locking technique is commonly used to obtain high peak power by generating short pulses in a laser cavity and the broad gain at ~2 ?m of
Thulium doped fiber allows potentially ultra-short pulse operation in modelocked laser. The saturable absorbers such as semiconductor saturable absorber mirror (SESAM), polarization beam splitter (PBS), fiber loop mirror, carbon nanotube (CNT), graphene and topological insulator have been deployed passively mode-locked fiber lasers. The saturable absorber based on topological insulators has been attracting much attention due to its broad operation wavelength comparing to the other methods, and simplicity for forming the fiber based saturable absorption devices such as a sandwiching method, a D-shaped fiber, a tapered fiber. In this paper, we proposed all fiber saturable absorption devices that has spectral filtering property using a bismuth telluride and MMI interaction. By deploying the proposed MMI based saturable absorber, a wavelength fixed passively mode locked thulium doped fiber laser was demonstrated operating at a wavelength of 1958 nm. The optical bandwidth of ~4 nm is experimentally obtained at a repetition rate of 22.7MHz.
We proposed a stable and narrow-linewidth wavelength swept laser source at the 800 nm region using an acousto-optic tunable filter (AOTF) and a passive fiber ring resonators (FRRs). In swept-source optical coherence tomography (SS-OCT), factors of wavelength swept laser such as linewidth and wavelength stability are dependent on the image depth and image stability. It is consists by a semiconductor optical amplifier (SOA), a fiber isolator, a fiber coupler, an AOTF and two passive FFRs. Conventional sweeping has been performed by mechanical filter such as fabry-perot tunable filter (FFP-TF) and galvanometer. However, mechanical movement complicates the device design and thus induces the limited stability and tuning speed. Recently, it has been known that AOTF is capable of yielding stable and fast performance. It offers a wide tuning range, high tuning speed and stable operation against vibration and temperature due to non mechanical. The narrow linewidth is realized by a passive fiber ring resonators (FRRs), which consists of two FRRs. Owing to the vernier effect, each lasing modes can be significantly suppressed to obtain the narrower linewidth. As a result, the single longitudinal mode can be successfully demonstrated. The FFRs, which corresponds to a longitudinal mode space of each length, are implemented by simply connecting ports of 3-dB fiber
9728-113, Session PTue
Wongeun Song, Advanced Photonics Research Institute
(Korea, Republic of) and The Univ . of Seoul (Korea,
Republic of); Minwan Jung, Advanced Photonics Research
Institute (Korea, Republic of) and Univ . of Seoul (Korea,
Republic of); Daeyoung Kim, Advanced Photonics
Research Institute (Korea, Republic of); Ju Han Lee, The
Univ . of Seoul (Korea, Republic of); Bong-Ahn Yu, Woojin
Shin, Advanced Photonics Research Institute (Korea,
Republic of)
We firstly proposed all-fiber band pass filter (BPF) operating at 2 um wavelength using concatenation of long period fiber grating (LPFG), null core silica fiber (NCSF) and long period fiber grating (LPFG). The first and the second LPFG have same resonance dip. When the light has met the first LPFG, according to phase-matching condition, the fundamental core mode couples to the cladding mode and the Rest of light except the first
56 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
LPFG’s resonant wavelength continues to propagate through the core of the fiber and it experiences high transmission loss at NCSF section. Therefore,
NCSF plays the role of core mode blocker in this structure. At the second grating, the cladding mode light is coupled to the core mode at the second
LPFG that has same resonant wavelength of the first LPFG. After the light pass through the proposed LPEG-NCSF-LPFG structure, it shows band pass filtering characteristics at resonance wavelength of LPFG pair. The distance between the two LPFG centers including the NCSF segment was less than 70 mm and the total length of the device was less than 120 mm.
The fabricated BPF has 4.2 dB insertion loss and less than 1 dB polarization dependence loss (PDL). The full width half maximum of transmission band is measured about 12.4 nm. The transmission of non-resonant signals were suppressed more than 6 dB. In order to evaluate the proposed device as a wavelength selective device, a wavelength selective Thulium doped fiber was demonstrated using the proposed device as a wavelength selector in the laser cavity. As the proposed device has a merit of all fiber device such as cost-effective, compactness and high power endurable, the proposed device could be used as an all fiber wavelength selective component in various applications at 2 um wavelength.
9728-116, Session PTue
Jan Szczepanek, Tomasz M . Kardas, Univ . of Warsaw
(Poland); Michal Nejbauer, Univ . of Warsaw (Poland) and Institute of Physical Chemistry (Poland); Czes?aw
Radzewicz, Institute of Experimental Physics, Faculty of
Physics, Univ . of Warsaw (Poland); Yuriy Stepanenko, Univ . of Warsaw (Poland) and Institute of Physical Chemistry
(Poland)
9728-114, Session PTue
Zeinab Sanjabi Eznaveh, J . E . Antonio Lopez, Gisela López-
Galmiche, James Anderson, Axel Schülzgen, Rodrigo
Amezcua Correa, CREOL, The College of Optics and
Photonics, Univ . of Central Florida (United States)
In this paper we report an all-PM-fiber laser amplifier system seeded by an all-normal-dispersion oscillator mode-locked with a Nonlinear Optical
Loop Mirror (NOLM). The presented all-normal-dispersion cavity works in a dissipative soliton regime and delivers highly-chirped, high energy pulses above 2.5 nJ with full width at half maximum below 220 fs. After the all-
PM-fiber amplifying stage spliced directly to the output of the oscillator we received pulses with the energy above 42 nJ and time duration below 200 fs. The electrical field of optical pulses from the system was reconstructed using the SPIDER technique. The influence of nonlinear processes on the pulse temporal envelope was investigated.
9728-117, Session PTue
Jun Liu, Chujun Zhao, Shenzhen Univ . (China); Yanxia Gao,
Shenzhen University (China); Dianyuan Fan, Shenzhen
Univ . (China)
We propose and experimentally investigate a novel design of a microstructured single mode (SM), very large mode area (VLMA) ytterbiumdoped rod type fiber amplifier featuring an enhanced higher-order mode
(HOM) delocalization and efficient preferential gain in active fibers. The proposed fiber design consists of six high-index germanium-doped silica rods integrated asymmetrically in the cladding of the fiber structure in order to remove the reflection symmetry and therefore, weakening the overlap of the LP11-like modes with the fiber core. This innovative fiber design with a core diameter of 66?m enables effective SM operation close to diffraction limited beam quality M2 of 1.3 in a broad spectral range of 850-1600nm with mode field area (MFA) of 2560um2 at 1064nm. The enhanced features of this fiber implies the improved threshold like onset of modal instabilities in high power fiber amplifiers.
To prove the robust SM operation of the fiber under any launching condition, we translated the input beam along x from -30?m to +30?m attempting to excite any HOM and recorded a series of near field images at 1064nm wavelength. No HOM was observed which confirms the effective SM operation of the asymmetric rod fiber.
To demonstrate highly effective HOM delocalization, the spatially and spectrally (S2) resolved mode imaging measurement was used to yield the mode images as a function of group delay. The peaks in the FT spectrum were corresponding to the cladding modes which particularly proves the scalability of the HOMs’ filtering capability of the proposed fiber design.
We experimentally demonstrate the operation of a stable harmonically mode-locked Raman fiber laser based on the nonlinear polarization rotation technique. A maximum average output power of up to 235 mW is achieved at the repetition rate of 466.2 MHz, corresponding to the 1695th order harmonic mode-locking operation. The temporal width of the mode-locked pulse train is 450 ps. The experimental results should shed some light on the design of wavelength versatile ultrashort lasers with high average output power.
9728-118, Session PTue
Daniel Creeden, Jon Blanchard, Herman Pretorius, Julia
Limongelli, Scott D . Setzler, BAE Systems (United States)
9728-115, Session PTue
Teppo Noronen, Oleg G . Okhotnikov, Tampere Univ . of
Technology (Finland)
No Abstract Available
Compact, high power blue light in the 470-490nm region is difficult to generate due to the lack of laser sources which are easily convertible
(through parametric processes) to those wavelengths. By using a pulsed
Tm-doped fiber laser as a pump source for a 2-stage second harmonic generation (SHG) scheme, we have generated ~2W of 486.5nm light at
500kHz pulse repetition frequency (PRF). To our knowledge, this is the highest PRF and output power achieved in the blue region based on a frequency converted, monolithic fiber laser. This pump laser is a pulsed
Tm-doped fiber laser/amplifier which generates 12W of 1946nm power at
500kHz PRF with diffraction-limited output from a purely single-mode fiber.
The output from this laser is converted to 973nm through second harmonic generation (SHG). The 973nm is then converted to 486.5nm via another
SHG stage. This architecture operates with very low peak power, which can
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications be challenging from a nonlinear conversion standpoint. However, the low peak power enables the use of a single-mode monolithic fiber amplifier without undergoing nonlinear effects in the fiber. This also eliminates the need for novel fiber designs, large-mode area fiber, or free-space coupling to rod-type amplifiers, improving reliability and robustness of the laser source. Higher power and conversion efficiency are possible through the addition of Tm-doped fiber amplification stages as well as optimization of the nonlinear conversion process and nonlinear materials. In this paper, we discuss the laser layout, results, and challenges with generating blue light using a low peak power approach. the laser’s stability. In this paper, an all-fiber kW-level narrow bandwidth amplifier with concise profile is demonstrated. The seed of the amplifier is an oscillator built on a pair of narrow bandwidth fiber Bragg gratings
(FBGs). The FBGs help to assure a narrow bandwidth output of the amplifier as 0.078 nm. The amplifier achieves near diffraction limited output of 823
W, which is the known highest power output for a narrow bandwidth fiber amplifier seeded by a FBG-based oscillator. And the opto-optic efficiency reaches 84.5%, which is rather high for a fiber amplifier, especially for a narrow bandwidth one. In the amplifier configuration, a newly designed cladding stripper with segment-based structure is brought in, realizing high efficiency and high power cladding light leakage. Besides, the mechanism of laser operation in a narrow bandwidth fiber amplifier is studied and simulated. Influences of seed and fiber parameters on SBS threshold in such amplifier are discussed as well, which provides guides in further power scaling of narrow bandwidth fiber lasers.
9728-119, Session PTue
Christian Kneis, Institut Franco-Allemand de Recherches de Saint-Louis (France) and Univ . Bordeaux 1 (France);
Thierry Robin, Benoît Cadier, iXFiber SAS (France);
Inka Manek-Hönninger, Univ . Bordeaux 1 (France); Marc
Eichhorn, Christelle Kieleck, Institut Franco-Allemand de
Recherches de Saint-Louis (France); Laurent Brilland,
Selenoptics (France); Johann Troles, Celine Caillaud,
Institut des Sciences Chimiques de Rennes, University of
Rennes (France)
9728-121, Session PTue
Jean-François Gleyze, Arnaud Perrin, Pierre Gouriou,
Florent Scol, Commissariat à l’Énergie Atomique (France);
Constance Valentin, Géraud Bouwmans, Lab . de Physique des Lasers, Atomes et Molécules (France); Emmanuel
Hugonnot, Commissariat à l’Énergie Atomique (France)
The generation of mid-infrared (mid-IR) radiation, ranging from 2 - 5 µ m, is getting much attention in the recent years thanks to many applications it can be used for, e.g. in free space optical communication systems, range finding and remote chemical sensing applications. It also plays an increasing role in medicine, for instance in optical tissue ablation or optical coherence tomography, owing to the high water absorption in that wavelength range. In this research study, a ZrF4-BaF2-LaF3-AlF3-NaF
(ZBLAN) fiber is pumped by a Q-switched mode-locked (QML) thulium
(Tm3+)-doped double-clad fiber laser, emitting at 2 µ m, to generate mid-IR supercontinuum (SC). Further spectral broadening is achieved by pumping a chalcogenide photonic crystal fiber (PCF) with the SC radiation from the
ZBLAN fiber. Different ZBLAN fiber designs and chalcogenide materials are characterized and compared regarding their potential for broadband high average output power performance. So far, 24 W of 2 µ m radiation in QML regime has been achieved with 5.1 W SC output power from the ZBLAN fiber. The broadest SC spectrum from the ZBLAN fiber went up to 4.1 µ m.
First proof of principal experiments with a germanium-arsenide-selenide
(GeAsSe) PCF fiber showed wavelength broadening up to 4.4 µ m with an output power level of 5 mW. The pump power has been 50 mW of SC radiation from the ZBLAN fiber with a spectrum from 3.5 µ m to 3.9 µ m.
The coupling efficiency of the ZBLAN radiation into the GeAsSe fiber has been around 30%. Power scaling of the SC generation in the ZBLAN and the chalcogenide fiber will be shown and further spectral broadening.
9728-120, Session PTue
Jinping Hao, Hong Zhao, Dayong Zhang, Liming Zhang,
Kun Zhang, North China Research Institute of Electrooptics (China)
Narrow bandwidth fiber laser has drawn increasing attention for its use in unique application areas such as gravitational wave detection, range finding, lidar, and coherent beam combination. However, power scaling of such laser is mainly prohibited by stimulated Brilliouin scattering (SBS) - one type of nonlinearity effects. Previous solutions to SBS limitation either call for additional control or increase the complexity of the laser, which could affect
In large scale laser facility dedicated to laser-matter interaction including inertial confinement fusion, such as LMJ or NIF, high-energy main amplifier is injected by a laser source in which the beam parameters must be controlled. For many years, the CEA has developed nano-joule pulses all-fiber front end sources, based on the telecommunications fiber optics technologies. Thanks to these technologies, we have been able to precisely control temporal shaping and phase-modulated pulse. Nowadays, fiber lasers are able to deliver very high power beams and high energy pulses for industrial needs (laser marking, welding,…). This new fiber laser technology has a great potential to improve stability and versatility of high-energy system front-end.
Therefore, we have currently developed new nanosecond pulses fibered amplifiers able to increase output pulse energy up to the mJ level. These amplifiers are based on flexible fibers and not on rod type. This allows us to achieve a compact source.
To be compatible with main amplifier section injection, the Gaussian intensity profile of fibered system must be transformed into ‘top-hat’ profile.
To reach this goal, we have recently developed an elegant and efficient solution based on a single-mode fiber which directly delivers a spatially coherent ‘top-hat’ beam.
In this conference, we will present last results of mJ-class top-hat all-fiber laser system, the results and the industrial prototype which can be used as a front-end of high-power lasers or as a seeder for other types of lasers. We will discuss the opportunity of such a system in LMJ architecture.
9728-122, Session PTue
Hong Zhao, Nianjiang Chen, North China Research
Institute of Electro-optics (China)
Narrow linewidth fiber lasers are wide applied in coherent detection, gravitational wave detection, coherent beam combing and wavelength
58 SPIE Photonics West 2016 · www.spie.org/pw
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beam combining.But in HPNL fiber laser, the main limitation factor of power increasing is SBS. Through sinusoidal phase modulating single frequency laser, we can increase longitudinal mode number. And then SBS can be suppressed. So, the keystone of sinusoidal phase modulation is analyzed.
The keystone of sinusoidal phase modulation is LiNbO3 crystal composing phase modulator, its refractive index changing under outward electric field influence and then input light wave modulated. The light that is inputted into phase modulator is called carrier frequency.The light spectrum broadening is the full width at half maximum (FWHM) of waveform envelope, which is composed with these sideband frequency spectrums.
The frequency distribution of sinusoidal phase modulating single frequency laser is simulated. The electrical frequency is 150MHz. Phase modulating coefficient is.
The laser is composed of seed source adding three stage amplifier.
Wherein, single frequency laser diode is employed as the seed source with
50mW, 1064.34nm and less than 1MHz. The phase modulator is employed to broaden spectrum. Its electro optical bandwidth, half wave voltage, maximum modulating voltage peak to peak value and maximum endured optical power are 150MHz, 2.5V, 20V and 20dBm, respectively. High frequency signal generator is employed as sinusoidal electrical signals to trigger source. Its output frequency range and maximum output power are 65kHz to 8GHz and 16dBm, respectively. The radio frequency driver
(RF driver) is used to amplify electrical signals. Its cut-off frequency, saturated output power and maximum gain are 20GHz, 26dBm and 30dB, respectively. In experiment, the signal generator output frequency is
150MHz. The phase modulating coefficient are , and , respectively.
In the first and second amplifier stage, Yb3+ doped double cladding fiber with core/cladding diameter of 10/130?m and length of 3m is employed as gain fiber (10/130 YDF). Its absorption coefficient is 3.9dB/m at 975nm.
In the third amplifier stage, Yb3+ doped double cladding fiber with core/ cladding diameter of 25/400?m and length of 12m is employed as gain fiber
(25/400 YDF). Its absorption coefficient is 1.6dB/m at 976nm.
To prevent feedback, an optical isolator (ISO) is connected between each stage. The second and third amplifier stage is connected by mode field adaptor (MFA). In order to eliminate the cladding light, the cladding light stripper is connected between the third and output end. In order to prevent the backward scattering light bashing the front stage device, a tap coupler is connected between the second and three amplifier stage. Its splitting ratio is 5/95. Its function is to monitor reverse SBS power (SBS monitor).
When the reverse power growing nonlinearly, showing that SBS has reached threshold. In this moment, the amplifier stage power supply should be shut off quickly to prevent the front stage device being bashed.
9728-41, Session 9
Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
(Invited Paper)
John D . Hybl, Darren A . Rand, MIT Lincoln Lab . (United
States)
There is continuing interest in increasing the power and improving the beam quality of laser sources for a variety of applications including materials processing, pumping, power transmission, and illumination. One approach is to continue to develop improved lasers with higher power and good beam quality. Another approach, particularly relevant to semiconductor and fiber lasers, is to beam combine large arrays of lasers. Beam combining has become increasing viable over the past decade as the community has developed a better understanding of the requirements imposed by beam combining, and various implementations have been successfully demonstrated in the laboratory. These implementations are beginning to see commercial application.
Key metrics for high-power arrays include the output power, the brightness, and the spectral width. To achieve high brightness, both high power and good beam quality are required. High-power diode arrays currently are composed of large numbers of emitters tiled side-by-side with the emitters being mutually incoherent with respect to each other. As the number of array elements increases, the beam quality decreases, and the brightness can be no better than that of an individual element. This is known as side-by-side beam combining. Polarization beam combining is often used to combine two arrays of orthogonal polarization. This can increase the brightness a factor of 2 at best.
There are two approaches, wavelength beam combining (WBC) and coherent beam combining (CBC), to scaling the brightness by large amounts, in principle by as much as the number of elements. In WBC, the array elements operate at different wavelengths and a dispersive optical system is used to overlap the different wavelengths spatially. Typical dispersive optical systems use gratings, prisms, or wavelength-selective reflectors. This is equivalent to what is done in wavelength division multiplexing for optical communications. The differences here are that the goal is higher power, and, therefore, the efficiency is more important. In
CBC, the beams are interferometrically combined, or phased. If the beams are phased properly, then constructive interference occurs and the power can be combined into a single beam.
This tutorial will cover the fundamentals of laser beam combining, including requirements on the array elements, basic scaling laws, and implementations. Examples from the literature will be used to show the progress being made.
9728-42, Session 9
Arno Klenke, Friedrich-Schiller-Univ . Jena (Germany) and Helmholtz Institute Jena (Germany); Michal Wojdyr,
Michael Müller, Friedrich-Schiller-Univ . Jena (Germany);
Marco Kienel, Friedrich-Schiller-Univ . Jena (Germany) and Helmholtz-Institute Jena (Germany); Jens Limpert,
Andreas Tünnermann, Friedrich-Schiller-Univ . Jena
(Germany) and Helmholtz-Institute Jena (Germany) and Fraunhofer-Institut für Angewandte Optik und
Feinmechanik (Germany)
Coherent combination of multiple amplifiers has become an established technology to overcome limitations of the average power, peak power and pulse energy of fiber-CPA systems. However, so far, these systems were built by duplicating standard single amplifier systems and adding the necessary components to realize the combination process. This limits the realistically achievable number of channels due to constraints of the footprint and component count. Therefore, the integration of multiple signal channels in a multicore fiber is of major interest.
In this contribution, we present coherent combination using an ytterbiumdoped multicore fiber as the main amplifier in a femtosecond fiber-CPA system. The fiber possesses four signal cores with a mode-field diameter of 36 µ m each and a shared pump cladding. The incident beam from the frontend is split into four parallel beams with a segmented-mirror splitter
(SMS). This splitter consists of a high reflective mirror and a second mirror with zones of different reflectivities. The beams are coupled into the signal cores of the multicore fiber and after amplification, they are recombined into a single beam again using a second SMS. A LOCSET stabilization system is employed to optimize the path lengths for constructive interference at the output. After compression, the system can emit up to 120 µ J pulses with a duration of 250 fs and a drastically improved pulse quality compared to a single core fiber. Due to the compact setup of this amplifier, laser systems with a large number of coherently combined channels will be realizable in the future.
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
9728-43, Session 9
Martin Gebhardt, Friedrich-Schiller-Univ . Jena (Germany) and Helmholtz Institute Jena (Germany); Christian Gaida,
Fabian Stutzki, Friedrich-Schiller-Univ . Jena (Germany);
Steffen Hädrich, Friedrich-Schiller-Univ . Jena (Germany) and Helmholtz Institute Jena (Germany); Cesar Jauregui,
Friedrich-Schiller-Univ . Jena (Germany); Jens Limpert,
Andreas Tünnermann, Friedrich-Schiller-Univ . Jena
(Germany) and Helmholtz Institute Jena (Germany) and Fraunhofer-Institut für Angewandte Optik und
Feinmechanik (Germany)
In a proof-of-principle experiment of cascaded coherent pulse stacking, an amplified chirped-pulse burst mainly consisting of four equal amplitude pulses is coherently stacked into a single output pulse using two cascaded
GTIs with a normalized pulse energy enhancement of 3.64 times. Input pulse burst is modulated using electro-optic modulators directly after a 122MHz mode-locked oscillator and a stretcher, and amplified into the microjoulemillijoule range prior to stacking using an amplification chain with a final
55?m chirally-coupled-core (CCC) fiber amplifier.
Cascaded pulse stacking opens a path to extracting all stored >10mJ pulse energy in ultrashort pulses from a fiber CPA system with negligible nonlinear distortions.
9728-45, Session 9
Michael Mueller, Marco Kienel, Michal Wojdyr, Arno Klenke,
Jens Limpert, Andreas Tünnermann, Friedrich-Schiller-
Univ . Jena (Germany) Complementing ultrafast thulium-based fiber-laser systems with subsequent nonlinear pulse compression can enable unique laser parameters at around
2 µ m operation wavelength. Significant pulse shortening and peak power enhancement have been accomplished using a fused silica solid-core fiber. In this fiber a pulse peak power of 24 MW was achieved without catastrophic damage due to self-focusing.
As compared to operation in the well-explored 1 µ m wavelength regime increasing the emission wavelength to 2 µ m is of twofold advantage for nonlinear compression in fused-silica solid-core fibers. This is because on the one hand the self-focusing limit scales quadratically with the wavelength. On the other hand the dispersion properties of fused silica allow for self-compression of ultrashort pulses beyond 1.3 µ m wavelength, which leads to strong spectral broadening from very compact setups without the need of external compression. Using this technique we have generated 1 µ J-pulses with 24 fs FWHM pulse duration (<5 optical cycles),
24 MW peak power at 24 W of average power. To the best of our knowledge, this is the highest average power obtained from any nonlinear compression experiment around 2 µ m wavelength and, the first demonstration of peak powers beyond 20 MW within a fused-silica solid-core fiber. This result is of significant importance for the development of interesting driving sources for high-field physics applications. It further emphasizes that thulium-doped fiber-based chirped-pulse amplification systems may outperform their ytterbium-based counterparts in terms of peak power due to the fourfold increase in the critical power for self-focusing.
Today, high-power femtosecond laser systems enable demanding industrial and scientific applications. The occurrence of nonlinear effects up to optically induced damage limit performance scaling, even after applying elaborate methods such as chirped-pulse amplification. Coherent beam combination and divided-pulse amplification are promising techniques to exceed the current limitations by temporally increasing the beam area and the pulse duration, respectively. Actively stabilized implementations achieved the highest combining efficiencies even for strong amplifier saturation and large nonlinear phase accumulation. However, the system complexity and the alignment sensitivity grow fast – asking for higher system integration.
In this contribution, we present a spatiotemporal combining setup in a proof-of-principle experiment with an entirely fiber-coupled front-end.
Unlike in previous experiments, where the temporal pulse division was achieved using free-space optical delay lines, the pulses are taken directly from the pulse train of the oscillator. Also the spatial division is totally fiber coupled. Thereby, the free-space paths and the alignment requirement are cut in half. However, the combination inevitably remains in free-space considering application in high-power lasers. For the combination of
4 pulses, a combining efficiency larger than 95% is demonstrated. The efficiency is largely independent of the combined pulse energy and the temporal pulse contrast is better than 20 dB.
Potentially, this approach allows for self-optimization of the combination due to the many degrees of freedom accessible with the EOMs.
9728-44, Session 9
Tong Zhou, John M . Ruppe, Cheng Zhu, John A . Nees,
Univ . of Michigan (United States); Russell B . Wilcox,
Lawrence Berkeley National Lab . (United States); Almantas
Galvanauskas, Univ . of Michigan (United States)
9728-46, Session 10
Daniel Creeden, Herman Pretorius, Julia Limongelli, Scott
D . Setzler, BAE Systems (United States)
We are developing a new technique of cascaded coherent pulse stacking
(CPS) for enhancing ultrafast pulse energies from fiber chirped-pulse amplification (CPA) systems by a factor of up to 100-1000 times. It is based on coherent temporal combining of a sequence of amplified chirped equal-amplitude input pulses into a single chirped output pulse using Gires-
Tournois interferometers (GTI). Cascaded CPS is accomplished with a burst of N equal-amplitude input pulses by storing all the energies of the first N-1 input pulses in the cavities through destructive interference at the partial reflector of the final GTI, followed by sequential extraction of the energy from each cavity through constructive interference of the N-th pulse with the intra-cavity pulses at the partial reflectors. The GTI roundtrip length can be folded using Herriott cells, which are essentially compactly folded optical delay lines and can greatly reduce the footprint of the GTIs.
High power fiber lasers/amplifiers in the 1550nm spectral region have not scaled as rapidly as Yb-, Tm-, or Ho-doped fibers. This is primarily due to the low gain of the erbium ion. To overcome the low pump absorption, Yb is typically added as a sensitizer. Although this helps the pump absorption, it also creates a problem with parasitic lasing of the Yb ions under strong pumping conditions, which generally limits output power. Other pump schemes have shown high efficiency through resonant pumping without the need for Yb as a sensitizer. Although this can enable higher power scaling due to a decrease in the thermal loading, resonant pumping methods require long fiber lengths due to pump bleaching, which limits the power scaling which can be achieved for single frequency output. By using an
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Er:Yb fiber and pumping in the minima of the Yb pump absorption at
940nm, we have been able to simultaneously generate high power, single frequency output at 1560nm while suppressing the 1-micron ASE and enabling higher efficiency compared to pumping at the absorption peak at 976nm. We have demonstrated single frequency amplification (540Hz linewidth) to 207W average output power with 49.3% optical efficiency
(50.5% slope efficiency) in an LMA Er:Yb fiber. We believe this is the highest reported efficiency from a high power 9XXnm pumped Er:Yb-doped fiber amplifier. This is significantly more efficient that the best-reported efficiency for high power Er:Yb doped fibers, which, to-date, has been limited to ~41% slope efficiency.
9728-47, Session 10
Jeffrey W . Nicholson, Anthony M . DeSantolo, Man F . Yan,
Patrick W . Wisk, Brian J . Mangan, Gabe S . Puc, OFS Fitel
LLC (United States); Anthony W . Yu, Mark A . Stephen,
NASA Goddard Space Flight Ctr . (United States)
Very-large-mode area (VLMA) Er-doped fiber amplifiers , core pumped by high-power 1480 nm, Raman fiber lasers, generate diffraction limited, high energy pulses at 1.5 micron wavelengths, and have applications in femtosecond fiber chirp-pulse amplifiers [ ] and high-energy soliton generation, for example. They have been demonstrated with core diameters greater than 50 microns and effective areas greater than 1100 square microns.
In spite of the success of VLMA Er amplifiers, there have been few results on making polarization maintaining large-mode area Er-doped fibers. A
26 micron mode-field diameter (~ 530 square micron Aeff) polarization maintaining, Er-Yb doped photonic crystal fiber laser was previously demonstrated. In this work, we demonstrate for the first time, a polarization maintaining, Er-doped VLMA amplifier with greater than 1000 square micron effective area. We then use this amplifier to demonstrate high energy, one microsecond pulse amplification at 1572.3 nm. The CO2 absorption line centered at 1572.3 nm has been chosen due to confluence of several spectroscopic properties. It is relatively insensitive to temperature changes compared to other lines in the absorption band, free of absorption features from other atmospheric constituents, and has a convenient peak absorption amplitude that allows measurement of the full atmospheric column that optimizes SNR (i.e - it does not saturate, but is a large enough feature that it is easy to distinguish from background variations.).
Single frequency, 1572.3 nm, 1 microsecond pulses at 7.2 kHz repetition frequency were amplified to 400 W peak power with a pulse energy of 368 microJoule. Polarization extinction ratio of the signal was better than 20 dB, and M2 = 1.1.
9728-48, Session 10
Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
Jun Zhang, Youming Chen, Radha Pattnaik, Mark Dubinskii,
U .S . Army Research Lab . (United States); Shibin Jiang,
AdValue Photonics, Inc . (United States)
A triple-clad silicate glass fiber with highly Er–doped core has been studied in a resonantly (in-band) pumped fiber laser configuration. Over 100 W laser output power at 1615.3 nm has been achieved with laser diode pumping at
~1530 nm and an optimized fiber length. To the best of our knowledge, it is the highest output power ever achieved from the fiber laser based on a silicate glass fiber. An efficiency of 55% (laser output versus absorbed pump power) was achieved in this first major power scaling experiment.
1. Introduction
Efficient power scaling of eye-safe Yb-free Er-doped silica fiber lasers based on 4I13/2 ? 4I15/2 transitions of Er3+ ions is hindered by low Erbium concentration due to low solubility of Er and a trend of Er ions to clustering in silica glass fibers. A typical core pump absorption of Erbium doped LMA silica fiber at 1530 nm is ~ 60 dB/m which is ~20 times lower than that of
Yb doped silica LMA fibers (1200 dB/m). Due to the low core absorption a much smaller clad-to-core ratio is required to retain reasonable clad absorption, which inevitably limits the total diode pump power that can be coupled in the cladding. Recent development of Er-doped silicate glass indicates that the novel silicate material is able to accept much higher Er concentration before clustering, which results in a 300-500 dB/m core pump absorption. Recently, 75% laser efficiency was demonstrated with resonant pumping from the 100 µ m clad diameter silicate glass fiber [1].
Presented here are the results of resonantly (in-band) diode-pumped fiber laser power scaling with a new LMA triple-clad silicate glass fiber. Some of the fiber parameters are presented in Table 1.
13 individual InGaAsP/InP based, volume Bragg grating (VBG)-narrowed (??
= 2 nm FWHM), 1530-nm fiber coupled laser diode modules were combined into a single fiber output using a 13x1 ITF pump combiner. The combiner output is a 250 µ m, 0.46 NA fiber matching the pump cladding of the
Er-doped silicate fiber. Figure 1 indicates a simplified experimental setup.
A pair of Semrock filters performs as a sharp edge dichroic wavelength separator with ~40 dB extinction ratio between the pump and laser wavelengths. A VBG or a broadband HR mirror are used to provide >99% laser feedback. VBG with the HR bandwidth of 1.5 nm at 1570 nm provides a laser wavelength selection, as needed. Broadband HR mirror provides a non-selective laser feedback. The pump end of the fiber is a straight cleave with 5.2% Fresnel reflection. The output signal is reflected by the second pump filter and analyzed. Figure 2 shows the laser performance of the fiber.
A fiber lengths of 10, 7, and 3 meters were used for Figure 2 shows the laser performance of the fiber. A fiber lengths of 10, 7, and 3 meters were used for optimization of optical efficiency.
Over 100 W of CW output is achieved with the fiber of 10 meter length. 55% efficiency was observed with the fiber length of ~7 meters. Laser output was characterized spectrally and spatially. We found the fiber output to be nearly single-mode. We will present the fiber laser performance with two types of mirrors, VBG and non-selective broad band mirror. We also measured a pretty high propagation loss of 0.3 dB/m, which happens to be a major contributor to optical efficiency being much lower than the quantum defect limited. Due to relatively high heat deposition level fiber laser operation required water cooling. Due to observable fiber microdefects at this early development stage fiber damage occurs at the pumped fiber tips during high power operation. We believe that much better efficiency and operation stability can be achieved with improved material quality.
In conclusion, we have demonstrated a scalability potential of a newly developed triple-clad silicate glass fiber with highly Er–doped core. With resonant diode pumping we achieved a laser output power of over 100 W at
1615.3 nm which is believed to be the highest output power achieved from fiber laser based on a silicate glass fiber.
References:
1. Qiang, ZX; Geng, JH; Luo, T; Zhang, J; Jiang, SB, “High-efficiency ytterbium-free erbium-doped all-glass double cladding silicate glass fiber for resonantly-pumped fiber lasers”, Appl. Opt. 53 (4), pp. 643-647 (2014).
9728-49, Session 11
Fabio Di Teodoro, Raytheon Co . (United States); Friedrich
P . Strohkendl, Raytheon Space and Airborne Systems
(United States)
High-peak-power, eye-safe ns-pulse fiber sources are well suited to remote sensing owing to good atmospheric transmission, spectral compatibility
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with mature photo-detectors, reliance on telecom component/materials, and usability in environments where glint can reach bystanders.
To scale peak power with low nonlinear effects, fibers of larger cores are required, in which it is generally difficult to have at once good beam quality and support for tight coiling. To address this issue, we use the semi-guiding high-aspect-ratio-core (SHARC) fiber concept. SHARC fibers feature elongated rectangular cores. In the short dimension, the fiber core behave as those in single-mode or large-mode area fibers. Tight coiling is thus possible. In the orthogonal, elongated dimension, all modes are actually leaky, the fundamental transverse mode being favored by differential loss design. Confined rare-earth-doping further helps select the fundamental mode via the greater spatial overlap with the transverse doping profile.
We amplified 1ns, 30kHz-rep.-rate, 1560nm pulses in an Er-doped SHARC fiber having mode-field area of approximately 2000 sq. microns. The fiber
(~5m long) was coiled at ~15cm diameter and in-band core-pumped by a
1470nm Raman fiber laser. In-band core-pumping provides low quantum defect heating and high pump absorption per unit length, which permit the use of short, lower-nonlinearity, fibers while keeping waste heat removal manageable. From the SHARC fiber, we obtained peak power ~ 100 kW with good spectral and spatial quality. Much higher peak power is anticipated in other SHARC fibers being developed characterized by mode areas > 20,000 sq. microns and same coiling diameters.
9728-50, Session 11
Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
Franz Beier, Friedrich-Schiller-Univ . Jena (Germany);
Matthias Heinzig, Till Walbaum, Nicoletta Haarlammert,
Thomas Schreiber, Ramona Eberhardt, Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany);
Andreas Tünnermann, Friedrich-Schiller-Univ . Jena
(Germany) and Fraunhofer-IOF (Germany)
9728-51, Session 11
Guancheng Gu, Clemson Univ . (United States); Zhengyong
Liu, The Hong Kong Polytechnic Univ . (Hong Kong, China);
Fanting Kong, Clemson Univ . (United States); Hwa-Yaw
Tam, The Hong Kong Polytechnic Univ . (Hong Kong,
China); Ramesh K . Shori, SPAWAR Systems Ctr . (United
States); Liang Dong, Clemson Univ . (United States)
Thermal management is critical for kw-level power lasers, where mode instability driven by quantum defect heating is a major challenge. Tandem pumping using 1018nm fiber lasers are used to enable both high brightness and low quantum defect. It is, however, difficult to realize efficient 1018nm
YDFL. The best demonstration to date is limited by the use of both conventional aluminosilicate host and smaller core diameters. In these cases, higher inversion is required due to the aluminosilicate host and higher pump brightness is required due to the smaller core, which results in high signal brightness for the same output power. These factors lead to large pump power to exit fiber, resulting in poor efficiency. Phosphosilicate host, on the other hand, requires much lower inversions to reach the gain threshold at
1018nm. The combination of phosphosilicate host and large-core leakage channel fibers (LCF) is a perfect candidate for efficient 1018nm fiber laser.
We report a highly efficient Yb-doped phosphosilicate LCF laser with a quantum defect of 4.1% using a ~50 µ m-core diameter and ~420 µ m cladding diameter. The slope efficiency with respect to the launched pump power at 1018nm is 70%. The ASE suppression is >60dB. The large cladding of
420 µ m demonstrates a combination of high efficiency, ~4% quantum defect and high-power low-brightness diode pumping. We have also studied the limits of operating ytterbium fiber lasers at shorter wavelengths and found the efficiency to fall off at shorter wavelengths due to the much higher inversions required.
The output power scalability of Ytterbium doped high-power fiber lasers is limited by several effects, e.g. mode instabilities and the thermal destruction of the rare earth doped fiber as well as of passive components. Since mode instabilities are a thermo-optical effect, the longitudinal thermal load and the resulting temperature distribution are of high interest to develop and substantiate the understanding of such limitations. We report on the measurement of the longitudinal temperature distribution in an amplifier fiber during high power operation. The measurement signal of an optical frequency domain reflectometer is coupled to an ytterbium doped amplifier fiber via a wave division multiplexer. The mode instability threshold of the fiber under investigation was determined to be 870?W. In a first experiment, the longitudinal temperature distribution was examined for different pump powers with a sub mm resolution. The results show even small temperature variations induced by slight changes of the environmental conditions along the fiber. With respect to the ytterbium ion interaction between 910 and
1150?nm, an OFDR laser source in the 1300?nm region was used. A clad light stripper prevents the passive optical components from the destruction by residual pump light. The longitudinal temperature distribution was determined for different pump powers up to a signal output power of
300?W. The mean temperature is increasing by an increased pump power and a maximum temperature increase of 10?K was measured. The qualitative progression of the longitudinal temperature distribution corresponds to the results of a rate equation simulation.
9728-52, Session 11
Vincent Petit, Richard P . Tumminelli, Coherent, Inc ., Salem
(United States); John D . Minelly, Victor Khitrov, Coherent,
Inc . (United States)
We report the fabrication of extremely low NA preforms (<0.03), highly doped with Yb using a conventional MCVD system. Our lowest NA preform was drawn to a 50um core step-index double-clad fiber operating in a single mode regime (M2=1.04). The fiber had an MFD and an Aeff greater than 35um and 1000um2 respectively. In a fiber laser configuration, the efficiency was greater than 85% without any sign of photodarkening. To the best of our knowledge, by using our extremely low NA preforms we have demonstrated the largest MFD and Aeff to date for a single-mode step index double–clad fiber without involving any micro-structuration.
9728-53, Session 11
Doruk Engin, Brian Mathason, Fibertek, Inc . (United
States); Mark A . Stephen, Anthony W . Yu, NASA Goddard
62 SPIE Photonics West 2016 · www.spie.org/pw
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Space Flight Ctr . (United States); He Cao, Jean-Luc
Fouron, Mark Storm, Fibertek, Inc . (United States)
A high energy (~2.5mJ), high average power (~20W), near transform limited
(<100MHz) and polarized 1572.3nm, erbium-doped fiber amplifier (EDFA) based transmitter is being developed for remote atmospheric CO2 sensing from space. Stimulated Brillouin Scattering (SBS) is a major obstacle for achieving required peak powers. A multi-aperture transmitter architecture utilizing cladding pumped erbium-yterbium (ErYb) fiber amplifiers is the most mature EDFA technology approach for achieving the high peak power requirements. Here, a cladding pumped polarization maintaining (PM) ErYb fiber based power amplifier optimized for high energy and high efficiency operation at 1572.3nm is presented. Using COTS PM ErYb fiber, the power amplifier, has been demonstrated to achieve 0.44kW peak power (440uJ pulse energy) and 3.3W average power with transform limited linewidth
(<10MHz). It has been shown that the power amplifier can support a
50% increase in pulse energy when the linewidth is increased to 100MHz.
Furthermore, a custom double clad ErYb LMA fiber has been designed and produced with slightly larger core and smaller clad sizes which is expected to support x2 the energies produced by the COTS LMA fibers. The fiber is fabricated with recently developed highly efficient ErYb core doping concentrations, including higher Er doping levels, which is expected to be especially favorable for efficient 1572nm amplification. Presentation will include measured performance of the novel ErYb fiber.
9728-54, Session 11
Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
Yaakov Glick, Yoav Sintov, Roey Zuitlin, Shaul Pearl,
Revital Feldman, Zvi Horvitz, Noam Shafir, Soreq Nuclear
Research Ctr . (Israel)
We have developed a high power SM fiber laser at 1018nm, producing 230W
CW, with an M2 ~ 1.1 and light to light efficiency of 75%. Interest in this wavelength has increased in the past few years due to its suitability for use as a pump fiber laser in tandem pumping configurations, mainly intended for obtaining high power fiber lasers. To the best of our knowledge this is the highest power described in the open literature from a SM fiber laser at this wavelength. One of the challenges of this type of laser is the low gain at this wavelength in comparison to that at ~1030nm, which may limit the power level achieved prior to the evolution of amplified spontaneous emission (ASE) at around 1030nm. As a result, effort must be implemented in order to inhibit lasing at this preferred wavelength range, which may, in turn, lead to damage to the laser due to the unstable nature of lasing resulting from sporadic reflections. We have employed careful simulations which take into account the various wavelength dependent parameters such as the fiber absorption, emission, saturation effects and the cavity mirror’s reflection, in addition to the fiber geometrical parameters (core/ clad diameters, length). The results of the simulations were calibrated to the experimental results obtained, and then used to design the reported laser.
Parameters that were found to be vital in suppressing higher wavelength lasing were the fiber length and the extinction ratio between the reflections of the FBG reflectors at 1018nm vs. at 1030nm.
9728-55, Session 11
Leonid V . Kotov, Fiber Optics Research Ctr . of the
Russian Academy of Sciences (Russian Federation) and
Moscow Institute of Physics and Technology (Russian
Federation); Albert Töws, Alfred Kurtz, Fachhochschule
Köln (Germany); Konstantin K . Bobkov, Fiber Optics
Research Ctr . of the Russian Academy of Sciences
(Russian Federation); Svetlana S Aleshkina, Fiber Optics
Research Ctr (Russian Federation); Mikhail M . Bubnov,
Fiber Optics Research Ctr . of the Russian Academy of
Sciences (Russian Federation); Denis S . Lipatov, Institute of Chemistry of High-Purity Substances of the Russian
Academy of Sciences (Russian Federation) and N .I .
Lobachevsky State Univ . of Nizhni Novgorod (Russian
Federation); Alexei N . Guryanov, Institute of Chemistry of High-Purity Substances of the Russian Academy of
Sciences (Russian Federation); Mikhail E . Likhachev, Fiber
Optics Research Ctr . of the Russian Academy of Sciences
(Russian Federation)
High-peak power monolithically build large mode area (LMA) polarizationmaintaining (PM) Er-doped fiber amplifier for Doppler wind lidar application is demonstrated. We developed novel double-clad single-mode PM LMA
Er-doped fiber as well as LMA PM passive components for light delivering and collection of backscattered Doppler signal. The active fiber core was based on P2O5-Al2O3-SiO2 glass matrix and had diameter of 36 µ m. This glass matrix allows one to improve pump conversion efficiency of the fiber and keep core-to-cladding refractive index difference low enough for single-mode operation regime. Despite of large core size the fiber has relatively low bend sensitivity and was winded with 10 cm diameter without significant bending loss. Optimization of stress rods size compound and position in active and passive fibers was done to provide high enough birefringence in LMA core and keep cladding size of 130 µ m.
We built a cladding-pumped at 980 nm co-propagating amplifier based on
5 m of developed active fiber and LMA passive components at the output.
Polarization extinction ratio at the output of the system exceeded 18 dB.
M2 of the amplifier output beam was measured to be less than 1.1. Amplifier was tested under 800 ns single-frequency seed pulses at 1556 nm and its stimulated Brillouin scattering threshold was found to be as high as 100 W.
Additionally, wind speed measurements were performed using the amplifier as the last stage in lidar system. The developed lidar system provides three times increase of measurement range compare to one based on standard telecom-grade amplifiers
9728-56, Session 12
Lars Rishoj, Gautam Prabhakar, Siddharth Ramachandran,
The Boston Univ . Photonics Ctr . (United States)
The effect of soliton self-frequency shift (SSFS) in optical fibers, i.e. intrapulse energy transfer to longer wavelengths via Raman scattering, has often been exploited for realizing wavelength tunable femtosecond fiber sources. One potentially attractive application of such tunable lasers is multiphoton microscopy, which requires energetic ultrafast pulses around
1300 nm. However, as solitons require anomalous dispersion (D > 0) it is only possible in conventional single mode fibers at wavelengths longer than
1300 nm, due to the material dispersion of silica. This constraint is lifted by highly confining the fundamental mode, as is commonly realized with photonic crystal fibers (PCFs). However, the small effective areas, typically
2-5 ?m2, limit obtainable pulse energies to sub-nJ levels. By utilizing stable higher order LP0,m modes, it is possible to lift this constraint as anomalous dispersion and large area are simultaneously achievable. In this work, we demonstrate continuous soliton shifting from a commercial 1030-nm fs laser up to 1314 nm, with output pulse energies of 12.5 nJ and widths of 75 fs using a 610 ?m2 mode-area LP0,9 mode in a multimode fiber. Significantly, this demonstration, of a fiber based tunable laser solution, is comparable to or exceeds energies obtainable from high-repetition-rate free-space commercial systems that provide sub-10-nJ energies at 1300 nm for multiphoton imaging applications.
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
9728-57, Session 12
Sven Breitkopf, Stefano Wunderlich, Friedrich-Schiller-
Univ . Jena (Germany) and Abbe School of Photonics
(Germany); Tino Eidam, Active Fiber Systems GmbH
(Germany); Evgeny Shestaev, Thomas Gottschall,
Friedrich-Schiller-Univ . Jena (Germany) and Abbe
School of Photonics (Germany); Henning Carstens, Max-
Planck-Institut für Quantenoptik (Germany) and Ludwig-
Maximilians-Univ . München (Germany); Simon Holzberger,
Ludwig-Maximilians-Univ . München (Germany); Ioachim
Pupeza, Max-Planck-Institut für Quantenoptik (Germany);
Jens Limpert, Friedrich-Schiller-Univ . Jena (Germany) and
Active Fiber Systems GmbH (Germany) and Helmholtz
Institute Jena (Germany); Andreas Tünnermann, Friedrich-
Schiller-Univ . Jena (Germany) and Helmholtz Institute Jena
(Germany) and Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany)
Passive steady-state enhancement cavities have been a subject of studies for several decades. Even though this technique is well known and the improvement of the pulse energy of high-repetition-rate lasers is something many applications ask for, the benefit of extracting the enhanced fs-pulses from such a resonator for applications outside of the cavity has not yet been fully exploited. We present a passive 30-m long enhancement cavity that supports a steady-state enhancement of 198, which is the highest enhancement that has ever been reached in such a long cavity. Furthermore, we demonstrate the extraction of a short burst with a total energy of 53.6
µ J employing an acousto-optic modulator (AOM) as a switching device. The cavity was seeded with pulses of 1.49 µ J energy at 10 MHz repetition rate.
The individual output coupled pulses showed an energy enhancement of up to 8.5 while the whole burst contained the entire energy of 36 input pulses.
The extraction of stretched fs pulses from such a long enhancement cavity has never been shown before.
the pulse to be amplified. After amplification in independent fiber amplifiers, the spectral parts are coherently combined to reconstruct an amplified spectrum that can be larger than in standard linear F-CPA configurations.
The experimental set-up starts with a mode-locked oscillator which is spectrally broadened to tens of nanometers and spectrally separated, through a dichroïc mirror, in two parts which are amplified in two different
Yb-doped fiber photonic-crystal fiber. The outputs of these amplifiers are then spectrally recombined and sent in a compressor. Coherent combining is ensured through active stabilization of the relative optical phase based on frequency tagging (LOCSET technique). In this configuration we are able to generate 10 µ J, 97 fs pulses at 1 MHz corresponding to an average power of
10 W.
9728-59, Session 12
Eitan E . Rowen, Nir Shalev, Eran Tal, Jacob Lasri, Eran
Inbar, Spectra-Physics Tel-Aviv (Israel)
Recently, fiber lasers have been incorporated in many industrial applications, due to their advantages in beam quality, wall-plug efficiency and low maintenance. Moreover, green and UV fiber-based lasers have been introduced, and have displayed the same advantages. One major drawback, compared to solid-state lasers, is the relatively low pulse energy that is extractable from a fiber amplifier.
In this report, we demonstrate a fiber based laser that generates bursts of >4mJ at a wavelength of 532nm in a pulse train of 70-300 pulses. The output of an Yb-doped fiber amplifier chain is doubled in a single pass through an LBO crystal with efficiency of above 65%. This high energy is obtained by temporal control of both the seed diode, and pump diodes.
The seed-diode generates a burst of pulses with a pulse width of 5-15ns at a frequency of 2-8MHz. Each burst is amplified to a peak power that allows efficient SHG in a chain of amplifiers, with pump diodes that are driven in pulses synchronized to the burst.
Such a solution may have many industrial and other applications, where fiber-based solutions have many advantages, but suffer a disadvantage of relatively low pulse energy.
9728-58, Session 12
µ
Florent Guichard, Marc Hanna, Lab . Charles Fabry
(France); Ronic Chiche, Lab . de l’Accélérateur Linéaire
(France); Yoann Zaouter, Amplitude Systèmes (France);
Fabian Zomer, Lab . de l’Accélérateur Linéaire (France);
Franck Morin, Clemens Hönninger, Eric P . Mottay,
Amplitude Systèmes (France); Patrick Georges, Lab .
Charles Fabry (France)
Fiber chirped-pulse amplifiers (F-CPA) are now widely recognized as a powerful tool for producing high average power and energetic pulses.
However the linear character of chirped-pulse amplification implies that gain narrowing limits the available pulse duration at the output of such systems to several hundreds of femtoseconds, typically around 200-300 fs. In the past few years, several schemes based on spectral coherent combining scheme have shown a strong potential to overcome such limitation. In this contribution we demonstrate the generation of ultrashort sub-100 fs pulse together with an output and compressed energy of 10 µ J. High output energy is achieved by incorporating a spectral coherent combining scheme into a large stretching ratio (1 ns) architecture, thus avoiding detrimental nonlinear effects. Femtosecond pulses emitted by an ultrashort oscillator are separated into several beams, each carrying a different spectral slice of
9728-60, Session 12
Mattia Michieletto, NKT Photonics A/S (Denmark) and DTU Fotonik (Denmark); Mette M . Johansen, DTU
Fotonik (Denmark); Jens K . Lyngsø, NKT Photonics A/S
(Denmark); Jesper Lægsgaard, Ole Bang, DTU Fotonik
(Denmark); Thomas T . Alkeskjold, NKT Photonics A/S
(Denmark)
The increasing demand of fibers able to delivery higher and higher average and peak power pulsed laser light, delivered undistorted and through several meters is pushing towards the development and exploitation of hollow core fibers. Hollow core fibers represent indeed the ideal candidate for beam delivery due to the minimal overlap between the fundamental mode and the silica, and therefore extremely low nonlinearities and high damage thresholds. In this work we demonstrated robust and bend insensitive fiber delivery of high power pulsed laser with diffraction limited beam quality for two different kind of hollow core photonic band gap fibers..
The light source for this experiment consists of ytterbium-doped double clad fiber aeroGAIN-ROD-PM85 in a high power amplifier setup. It provided
22ps pulses with a maximum average power of 95W, 40MHz repetition rate
64 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications at 1032nm (~2.4?J pulse energy), with M2 <1.3. We determined the facet damage threshold for a 7-cells hollow core photonic bandgap fiber and showed up to 59W average power output for a 5 meters fiber. The damage threshold for a 19-cell hollow core photonic bandgap fiber exceeded the maximum power provided by the light source and up to 76W average output power was demonstrated for a 1m fiber. In both cases no special attention was needed to mitigate bend sensitivity. The fibers were coiled on 8 centimeters radius spools and even lower bending radii were present.
In addition stimulated rotational Raman scattering arising from nitrogen molecules was measured through a 42m long 19 cell hollow core fiber.
9728-64, Session 13
(Invited Paper)
François Salin, MoriaLase / EOLITE Systems (France)
Since their invention in 2003 rod type fibers have found their way to applications in the industrial market. Their ability to provide high power short pulses with good beam quality makes them a strong competitor to classical bulk Nd:vanadate systems. I will review some of the historical success and failures of this technology with applications from Extreme UV lithography to solar cells.
9728-61, Session 12
Steven Brunton, J . Nathan Kutz, Univ . of Washington
(United States); Xing Fu, Nokia (United States)
Advanced methods in data science are driving the characterization and control of nonlinear dynamical systems in optics. In this work, we investigate the use of machine learning, sparsity methods and adaptive control to develop a self-tuning fiber laser, which automatically learns and adapts to maintain high-energy ultrashort pulses. We investigate the mode-locked laser that uses nonlinear polarization rotation (NPR) to achieve saturable absorption using wave plates and a polarizer. The optical components may be mechanically actuated with servomotors to tune the system and avoid the multi-pulsing instability. In particular, a two-stage procedure is introduced consisting of a machine learning algorithm to recognize different dynamical regimes, followed by an adaptive control algorithm to reject disturbances and track optimal solutions despite stochastically varying system parameters. The machine learning algorithm, called sparse representation for classification, comes from machine vision and is typically used for image recognition. The adaptive control algorithm is extremumseeking control, which has been applied to a wide range of systems in engineering; extremum-seeking is beneficial because of rigorous stability guarantees and ease of implementation. Together, these algorithms result in continuous high-performance operation, despite significant disturbances to the system, including large stochastic fluctuations of the birefringence.
9728-62, Session 13
(Invited Paper)
Jens Limpert, Friedrich-Schiller-Univ . Jena (Germany)
Rod-type photonic crystal fibers currently hold all the performance records of pulsed fiber laser systems with diffraction-limited beam quality.
Furthermore, these fibers constitute the ideal building blocks for the next generation high performance ultrashort fiber laser systems based on parallelization. In this talk, it will be discussed how giving away 10 years ago one of the most popular characteristics of an optical fiber, namely its flexible nature, has led to an enormous performance evolution of pulsed, and in particular femtosecond, fiber lasers. Additionally, new rod-type fiber designs and the operation in alternative wavelength regions will be presented.
9728-65, Session 14
µ
Dmitry Gaponov, NOVAE (France); Laure Lavoute, NOVAE
(France); Sébastien Février, XLIM Institut de Recherche
(France); Ammar A . Hideur, CORIA (France); Nicolas
Ducros, NOVAE (France)
During the last decade, a growing interest to high power ultrafast sources at 2 micron has emerged. This relatively new wavelength falls into the absorption band of some important organic materials and attracts a particular attention for material processing applications. However a number of physical and technological issues limit the development of powerful thulium-based ultrafast lasers. Nevertheless, a record level of 200 MW peak power was recently demonstrated. However, state-of-the-art systems are still at the stage of laboratory development and could hardly be integrated for industrial use.
In this work, we present our significant progress towards compact ultrafast high-power all-fibered lasers emitting in the 2 µ m wavelength range. An allfiber integrated oscillator based on the dissipative soliton concept delivers highly energetic and positively chirped pulses at a high repetition rate.
Pulses from this oscillator are then directly amplified in a classical master oscillator power amplifier scheme without the need for any pre-amplifier stage.
The seed oscillator emits 48 ps pulses at 1940 nm with 50 mW of average power at 10 MHz repetition rate. Direct amplification provides 2 W of average power and 120 kW of peak power after compression. By increasing further the threshold for optical nonlinearities in the amplifier by means of a fiber stretcher, the laser system delivers 4.3 W before compression and 220 kW of peak power for 900 fs recompressed pulses. To the best of our knowledge, this is the first demonstration of direct amplification of dissipative solitons in the 2 micron wavelength range.
9728-66, Session 14
Xiaolei Bai, Wei Shi, Quan Sheng, Tianjin Univ . (China)
9728-63, Session 13
(Invited
Paper)
Thomas Tanggaard Alkeskjold, NKT Photonics A/S
(Denmark); Jes Broeng, DTU Fotonik (Denmark)
No Abstract Available
High power single-frequency lasers in 1.5-?m eye-safe region with narrow spectrum linewidth are of great importance in applications of highresolution spectroscopy and coherent Doppler LIDAR. MOPA systems based on erbium: ytterbium (Er: Yb) co-doped fiber (EYDF) could achieve higher output power, narrower linewidth and better stability compared with other coherent sources for this region such as optical parametric oscillators and
Raman laser and therefore have being the most promising method. In 2004,
C. Alegria et al. demonstrated a single-frequency fiber MOPA with 83 W output power at 1552nm with linewidth of 13 kHz. Then in 2005, Y. Jeong et al. achieved a output power of 151 W. However, the MOPAs are still needed to be all-fiberized and the linewidth evolution during the amplification
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications has never been investigated. In this work, we demonstrate an all-fiber single-frequency EYDF MOPA system operating at 1550 nm with 56.4 W of maximum output power and a slope efficiency of 37.0%. The linewidth measurement based on delayed self-heterodyne interferometric technique shows the linewidth increases continuously with the pump power and a linewidth of 4.2 kHz is observed with the maximum output power of 56.4
W, which is the narrowest linewidth with over 50 W output power in this wavelength region ever reported.
9728-68, Session 14
Wenyan Tian, Yelena Isyanova, Robert A . Stegeman, Ye
Huang, Q-Peak, Inc . (United States); Logan R . Chieffo,
Peter F . Moulton, Q-Peak Inc . (United States)
9728-67, Session 14
Denis S . Kharenko, Institute of Automation and
Electrometry (Russian Federation) and Novosibirsk State
Univ . (Russian Federation); Anastasia E . Bednyakova,
Novosibirsk State Univ . (Russian Federation) and Institute of Computational Technologies (Russian Federation);
Evgenii V . Podivilov, Institute of Automation and
Electrometry (Russian Federation) and Novosibirsk
State Univ . (Russian Federation); Mikhail P . Fedoruk,
Novosibirsk State Univ . (Russian Federation) and Institute of Computational Technologies (Russian Federation);
Alexander A . Apolonskiy, Ludwig-Maximilians-Univ .
München (Germany) and Institute of Automation and
Electrometry (Russian Federation); Sergey A . Babin,
Institute of Automation and Electrometry (Russian
Federation) and Novosibirsk State Univ . (Russian
Federation)
High power picosecond green lasers are very attractive for high precision material processing and micromachining applications. Their unique features enable precision cutting and patterning of sensitive materials used in many advanced devices without the requirement for a post-process cleaning.
Although nanosecond green lasers based on intra-cavity frequency-doubled
Q-switched Nd-doped lasers have been one of the most popular green lasers and widely used in industrial laser-machining, they are not suitable for high precision material processing and micromachining due to relatively long pulse width and multi-mode beam quality.
We report the development of an all-fiber, near 70-KW peak power, 16-ps pulse-width, narrow bandwidth, linearly polarized, 1064-nm fiber laser suitable for high power picosecond green laser generation. Our 1064-nm fiber laser delivers average power up to 110 W in a narrow bandwidth with a minimal nonlinear distortion at a repetition of 100-MHz. We will report the development of high power picosecond green lasers at 532 nm based on single-pass frequency-doubling of our all-fiber based 1064-nm fiber laser in the nonlinear material LBO. Using a 15-mm long LBO crystal, we have generated 30 W of picosecond green laser average power with a conversion efficiency of 41% from a 73-W, 16-ps 100-MHz fiber laser. To our best knowledge, this is the highest average-power picosecond green laser generated from all-fiber, narrow bandwidth, linearly polarized, picosecond
Yb-doped fiber laser
Generation of highly-chirped dissipative solitons is a powerful technique to obtain high-energy femtosecond pulses in mode-locked lasers based on fiber or other solid-state active media. Energy scaling of the most powerful
Yb-doped fiber laser by means of cavity lengthening using PM fibers is known to be limited by the stimulated Raman scattering (SRS), converting the excess pulse energy to the red-shifted Stokes wave (Raman pulse).
Re-injection of the Raman pulse into the laser cavity with proper timing can form so-called Raman dissipative soliton (RDS), as we have shown recently.
Here we report on the first experimental demonstration of the cascaded generation of the higher-order RDS in similar scheme providing synchronous pumping of consecutive Stokes orders in the common cavity of Yb fiber laser by means of several intra-cavity feedback loops optimized for each order. The generated pulses (conventional dissipative soliton at 1020 nm, 1st and 2nd order RDSs at 1065 nm at 1115 nm, correspondingly) are shown to be linearly-chirped and compressible to 200-300 fs. Moreover, they appear to be mutually coherent that has been confirmed by efficient coherent combining exhibiting <40 fs interference fringes within the combined pulse envelope. The noise level grows with increasing order, but it can be reduced by a stronger spectral filtering, as shown by numerical simulation.
This approach opens the door towards cascaded generation of coherent dissipative solitons in a broad spectral range (so-called dissipative soliton comb) that can improve areas such as frequency comb generation, pulse synthesis, biomedical imaging and also emerge new applications.
9728-69, Session 14
Keiron Boyd, Simon M . Rees, Defence Science and
Technology Group (Australia); Nikita Simakov, Defence
Science and Technology Group (Australia) and Univ . of
Southampton (United Kingdom); Jae M . O . Daniel, Defence
Science and Technology Group (Australia); Robert
Swain, Eric W . Mies, Sub-Micron Engineering (United
States); Alexander V . Hemming, Defence Science and
Technology Group (Australia); W . Andrew Clarkson, Univ . of Southampton (United Kingdom); John Haub, Defence
Science and Technology Group (Australia)
CO2 laser processing facilitates contamination free, rapid, precise and reproducible fabrication of devices for high power fibre laser applications.
We present advances in CO2 laser fabrication techniques for cleaving of complex optical fibre designs and fabrication of cladding light strippers. Our end-face processing techniques utilize a 9.6 ?m CO2 laser to produce flat, smooth and symmetric fibre end-face profiles with no rounding or melting at the edges of the fibre, achieving fibre cleave angles of less than 0.06° and with a reproducibility better than 0.03° - this is an order of magnitude smaller than previously demonstrated CO2 processing approaches. To the best of our knowledge this is also the first demonstration of a CO2 process that has generated a fibre end-face topography substantially smaller than a typical mechanical cleave. We also investigate the challenges associated with controlled CO2 laser ablation of fibres with multiple layers of doped and un-doped glass as well as non-circular designs.
The efficient removal of excess cladding light at high optical power without degradation of core mode propagation or localized heating is of
66 SPIE Photonics West 2016 · www.spie.org/pw
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significant interest in the production and operation of compact, robust, high power fibre lasers and amplifiers. We present and characterize a CO2 laser technique for the fabrication of compact all glass cladding strippers with losses of up to 20dB/cm, tensile strength above the force required to mechanically cleave the fibre and core propagation losses of less than 0.016 dB/cm.
9728-70, Session 15
Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
Alexander Yusim, Igor Samartsev, Oleg Shkurikhin, IPG
Photonics Corp . (United States); Daniil V . Myasnikov, IRE-
Polus Co . (Russian Federation); Andrey Bordenyuk, Nikolai
Platonov, Vijay Kancharla, Valentin P . Gapontsev, IPG
Photonics Corp . (United States)
9728-72, Session 15
Aart Verhoef, Medizinische Univ . Wien (Austria) and
Technische Universtität Wien (Austria); Lingxiao Zhu, Univ .
Wien (Austria) and Technische Univ . Wien (Austria); Marco
Andreana, Medizinische Univ . Wien (Austria); Martin Distel,
St . Anna Kinderkrebsforschung e .V . (Austria); Stine Møller
Israelsen, Karsten Rottwitt, Technical Univ . of Denmark
(Denmark); Wolfgang Kautek, Univ . Wien (Austria);
Andrius Baltuska, Technische Univ . Wien (Austria); Alma del Carmen Fernandez Gonzalez, Medizinische Univ . Wien
(Austria) and Technische Univ . Wien (Austria); Wolfgang
Drexler, Angelika Unterhuber, Medizinische Univ . Wien
(Austria)
Ultrafast fiber lasers are widely used for medical and industrial applications due to their high efficiency, compact size, good beam quality, and excellent reliability. Pulse energy up to 10 microjoules are required for medical application such as cataract surgery and corrective eye surgery. Less than
100 microjoules is required for micromachining applications. Sufficiently short pulses less than 20 ps are used to minimize the heat affected zone and kerf through a process triggered by multiphoton absorption. Cutting speed is a critical parameter for industrial applications such as glass and sapphire cutting. High average power improves the speed of cutting these materials. Increasing the pulse repetition while keeping tight control of the pulse energy achieves the necessary cut quality at high speed. Fiber laser configuration is highly scalable with regards to average output power and is a good fit for high speed glass and sapphire cutting.
We report on industrial grade picosecond and femtosecond pulse Yb fiber lasers with >100 microjoule pulse energy and 100s of Watts of average power for improved laser machining speed of sapphire and glass. The highly efficient laser with >25% wall plug efficiency in a compact 3U rackmountable configuration has >2m fiber delivery cable. Customer reconfigurable features such as controllable repetition rate, fine pulse duration control, burst mode operation and adjustable pulse energy permit the customer to tailor the laser to their application.
We developed a semiconductor saturable absorber mirror modelocked all-
PM femtosecond fiber laser where for the first time a PM higher-order-mode fiber was used for intracavity dispersion compensation. The ring cavity of the oscillator has a repetition rate of 12 MHz, the total intracavity cavity dispersion is close to zero. The oscillator delivers 0.45 nJ pulses that can be externally recompressed down to 97 fs, which to the best of our knowledge are the shortest pulses generated from an all-PM Yb-fiber oscillator. The observed 1 Hz linewidth, absence of any sidebands, and 80 dB signal/ background ratio of the output pulse train measured with an RF spectrum analyzer with 1 Hz resolution bandwidth illustrate the excellent stability of the oscillator. To allow for stronger signals and faster data collection for nonlinear microscopy, we amplify the pulses in a PM single-mode Yb-fiber amplifier to ~20 nJ after stretching them with 100 m of PM980. Using a pair of grisms we recompress the pulses to ~150 fs duration.
With this source we have performed in-vivo nonlinear microscopy in zebrafish larvae, where we have simultaneously measured backscattered second harmonic and back-propagating fluorescence from two-photon excited red-fluorescent protein. To avoid optical damage to the larvae, the incident energy was limited to 5 nJ. Strong second harmonic signal can be observed from the collagen fibers in the tail finn, as well as from the muscles in a zebrafish tail. Fluorescence from macrofages labeled with mCherry, that can be used to identify cancer, is also observed.
9728-71, Session 15
Michael Walornyj, Jaroslaw Abramczyk, Kanishka Tankala,
Nils Jacobson, Nufern (United States)
9728-73, Session 15
Lalitkumar Bansal, Andrea Rosales-Garcia, OFS Fitel
LLC (United States); V . R . Supradeepa, Indian Institute of
Science (India); Thierry F . Taunay, Clifford Headley III, OFS
Fitel LLC (United States)
Large mode area (LMA) double clad fibers (DCF) are widely used in high power laser applications. Optical reliability of DCFs has been studied and a predictive model for determining the fiber lifetime has been reported. While tensile strengths and n-values have been reported for DC fibers, mechanical reliability of fibers used in high power laser applications has yet to be studied. In these applications, large diameter LMA fibers are often tightly coiled to suppress higher order modes to achieve SM operation as well as to minimize form factor. The mechanical stresses resulting from bending large diameter fibers can significantly exceed those seen in the telecom industry.
The mechanical reliability of telecom fibers has been thoroughly studied and models for predicting fiber lifetime for typical stresses experienced in deployment conditions are available. An analysis of the factors affecting the lifetime of DCF fibers in typical deployment conditions using such models has not been conducted. This paper, for the first time, will provide a comprehensive analysis all the factors impacting lifetime of LMA fibers.
Furthermore, it highlights the choices manufacturers and users of DCF can make to enhance the longevity of the fibers. Nufern’s LMA-YDF-20/400 used in kW class fiber lasers is used as a case study to illustrate the parameters that impact mechanical service lifetime of the fiber.
The power threshold for nonlinear effects in fiber lasers and amplifiers is inversely proportional to the fiber length. The required gain fiber length is in turn proportional to the cladding area of the gain fiber. In order to minimize nonlinearities, the smallest possible cladding diameter is desirable. On the other hand the amount of pump power that can be coupled into the gain fiber is proportional to its cladding area, and a large cladding is preferable.
In an all fiber source configuration, pump light can be injected into the gain fiber by using a tapered fiber bundle [1]. This consists of multiple pump fibers that are closely packed together, tapered down and spliced to an output fiber. The output fiber is typically the same diameter as the gain fiber. As the bundle is tapered, the NA of the light that can propagate through it increases with the taper ratio. For low loss, the brightness condition, shown in Eq. 1 should be satisfied.
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Conference 9728: Fiber Lasers XIII:
Technology, Systems, and Applications
D_o^2 ?NA?_o^2 ≥ ?nD?_in^2 ?NA?_in^2 (1)
Where Do/Din is the diameter of the output/input fiber, NAo/NAin is the numerical aperture of the output/input fiber, and n is the number of fibers in the bundle. The pump combiner design thus depends on the diameter and the NA of the diode pigtail fiber from a given diode manufacturer.
Combiners based on a single bundle with up to 19 pump arms are typically available with pump transmission of 95%. When a larger number of pump ports is required, a so-called tree architecture shown in Fig. 1 offers a superior approach. It consists of a number of pump combiners which are spliced to the pump arms of a 2nd stage pump-signal combiner. This architecture has the additional advantage of simplifying the design for PM performance.
A typical, industry-standard diode [2][3] uses 105/125 ?m (core/cladding) diameter pigtail fiber with light coupled into 0.15 NA. Based on Eq. (1) and using such diodes, typical commercially available 7x1 pump combiners designed to couple into 220/240 ?m diameter output fiber with 0.22 NA achieve pump transmission efficiency of about 90%.
To improve overall combiner performance, we have demonstrated a 1st stage pump combiner in which 7 diodes are combined into a 200/220 um 0.22
NA output fiber, with an average transmission of 99%, as seen in Fig. 2a.
This improvement in pump combiner performance leads to a significantly improved high power tree pump combiner system. Figure 2b shows the transmission through the tree architecture using four such 7x1 multimode combiners. We have tested the optimized combiner system up to 1.3kW with 95% pump transmission efficiency and a thermal slope efficiency of
0.02 C/W, when heat sunk to a cooling plate at 25?C, the hottest spot was on the splice point which is 10 mm away from the fiber coating which is most prone to thermal damage. The (6+1)x1 PM single mode combiner has a 15/330 ?m output fiber with a signal loss of 0.2dB and a PER of 20dB. The overall pump transmission through the tree architecture is increase by 6% compared to trees based on commercially available combiners, offering a significant improvement in both efficiency and management of waste heat.
The key characteristic of the combiner system is summarized in Table 1. An additional advantage of the improved pump combiner is that the output pigtail fiber now has 330 ?m cladding diameter as opposed to 400um, offering a significant improvement in pump brightness. This will translate into an approximately 50% increase in nonlinear thresholds for gain fibers with the same fiber core properties, due to the reduction in fiber length.
With this device improved system efficiency, fewer diodes are needed, offering cost savings, and there is less burden on thermal management.
In summary, we demonstrate a (42+1)x1 PM cascaded combiner system, with a 330um output cladding diameter, that has a 6% improvement in pump transmission compared to a standard 400 ?m combiner system. In addition, with this smaller cladding, and a correspondingly shorter fiber length the threshold for nonlinearities will increase. The combiner system has a high pump efficiency of 95%, driven by high efficiency 99% pump combiners. The pump and signal combiner has passed a high power handling test of 1.3 kW with thermal slope of 0.02 C/W, limited by available diode power. beam profile with a specific angular divergence.
Here, a novel specialty fiber, made to satisfy the standard beam delivery
(BD) cable requirements and designed to tailor mode up-conversion in a low maintenance and cost-effective single fiber device is reported.
Using numerical simulations based on spatial mode overlap calculations between the SM launch and the BD fiber, the design is optimized in order to achieve the required beam profile and beam divergence. According to the modeling predictions, a specialty fiber with 100 um core and 360 um cladding was fabricated and characterized with less than 2 dB/km attenuation in the 1 um wavelength range. Flat-top beam profile with a 3.8
BPP was demonstrated out of this fiber when coupling light from a SM 20 um core, 0.06 NA and 400 um cladding fiber laser.
Numerical and experimental results will be detailed for 50, 100 and 200 um core diameter fibers delivering flat-top beam profiles with BPP values around 2, 4 and 8 mm x mrad respectively. Moreover, results of high power testing of the specialty fiber beam delivery cable at 2 kW laser power will be presented.
9728-75, Session 15
Chris McIntosh, Lew Goldberg, Brian J . Cole, Alan D . Hays,
U .S . Army RDECOM CERDEC NVESD (United States)
A compact 1030nm fiber laser for ultraviolet generation at 257.5nm is presented. The laser employs a 35cm long polarization-maintaining 20um core (0.07 NA), 130um clad (0.45 NA) ytterbium fiber. In order to ensure lasing in the fundamental mode, the fiber was coiled into a 30mm diameter.
One end of the fiber was flat-cleaved to serve as the output coupler, while the other end of the fiber was angle-cleaved. The light from a 975nm grating stabilized pump (0.1 NA, 105um clad diameter) was injected at a 15° launch angle using a 1:1 relay lens into the flat-cleave end of the fiber. A reflective long-pass filter was placed at the other fiber end to recycle the pump and a Cr:YAG saturable absorber (19% unsaturated transmission) was placed at the waist of a second 1:1 relay lens for passive Q-switching. A volume
Bragg grating (VBG) was employed as the mirror. The fundamental 1030nm output was 2.0W average (in a 125uJ pulse train) for 10W launched pump power. A 15mm length of lithium triborate (LBO) was chosen for second harmonic generation and a 7mm length of beta-barium borate (BBO) was used for the fourth harmonic generation. The second harmonic generation
(SHG) conversion efficiency was 38% (770mW) and the fourth harmonic generation (FHG) efficiency was 26% (200mW). The laser’s spectral linewidth was <0.1nm FWHM at 10W pump power, which should avoid broadening of Raman excitations when used for explosives spectroscopy.
9728-74, Session 15
Clémence Jollivet, Kevin F . Farley, Michael Conroy,
Jaroslaw Abramczyk, Nufern (United States); Steffen
Belke, Frank Becker, ROFIN-SINAR Laser GmbH
(Germany); Kanishka Tankala, Nufern (United States)
Most kW power level fiber laser systems operate in single-mode (SM) regime, preferred for its stable output performances with diffraction limited beam profile. However, several applications, including laser-assisted material processing, require kW-level beams with uniform intensity distribution such as flat-top profiles and controlled beam divergence. Therefore, there is a need for all-fiber devices able to up-convert the input SM into a uniform
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9729-1, Session 1
Greg A . Pitz, Air Force Research Lab . (United States)
Scaling of Diode Pumped Alkali Lasers (DPALs) has been demonstrated at the Air Force Research Laboratory (AFRL) at high power with excellent optical:optical slope efficiencies. Previously, a rubidium (Rb) dual flow
– Master Oscillator Power Amplifier (MOPA) configuration and a rubidiumcesium (Cs) Multi-Alkali Multi-Line (MAML) laser have been demonstrated.
New potassium (K) diode modules are anticipated to yield output power scaling to significantly greater than previously demonstrated values. Due to the small spin-orbit splitting between the 2P states of K as compared to
Rb and Cs, collisional relaxation can be achieved using noble gases in place of hydrocarbons. This will help mitigate the substantial challenge of alkali contamination of the optical windows caused by photochemical breakdown.
9729-2, Session 1
Randall Knize, Boris V . Zhdanov, Matthew Rotondaro,
Michael Shaffer, U .S . Air Force Academy (United States)
This talk presents the results of an experimental study of a Cs DPAL operating in pulsed and continuous wave (CW) modes with different buffer gases. We explored such buffer gases as Ethane (C2H6), Methane (CH4) and mixtures of these hydrocarbons with noble gases He and Ar. In these experiments we varied two parameters: buffer gas composition and the total buffer gas pressure to explore how these factors affect lasing efficiency of a Cs DPAL in pulsed and CW modes of operation. Using a pulsed pump source, we observed effects of DPAL output power degradation in time from its starting maximum value at the beginning of the pump pulse to its
CW level. We studied how the characteristic time of power degradation and power drop level depends on buffer gas content and pump power. Also we explored the possibility of mitigating of the power degradation effect by flowing the gain medium. transonic (M ~ 0.9) DPALs, taking into account fluid dynamics and kinetic processes in the lasing medium is reported. The performance of these lasers is compared with that of supersonic (M ~ 2.7 for Cs and M ~ 2.4 for K) DPALs.
The power achieved in the supersonic and transonic K DPALs is higher than for the subsonic version by ~ 84% and ~ 27%, respectively, showing an advantage of the supersonic device over the transonic and subsonic ones.
Comparison between end- and transverse-pumping by rectangular beams of the same cross section shows that in terms of brightness and beam quality, end-pumping geometry is preferred, although the output power is not affected by the pump geometry.
9729-4, Session 1
F . W . Hersman, The Univ . of New Hampshire (United
States) and Xemed LLC (United States); J . H . Distelbrink, J .
Ketel, J . Wilson, D . W . Watt, Xemed LLC (United States)
Diode lasers have high electrical-to-optical efficiency, but the spectral range of their output is too broad to be fully absorbed on alkali vapors.
One method for locking the output wavelength and reducing the linewidth is to feed light from a wavelength selective optical cavity back into the emitters. Ten years ago our team developed a stepped-mirror that allowed a single external cavity to lock the wavelength of a stack of diode array bars by equalizing path lengths between each emitter and the grating. Here we report a laser architecture that combines one such step-mirror external cavity with an array of power dividers, each of which sends a portion of this feedback power to a separate diode array bar stack. We have assembled a system with four beam splitters that distribute feedback power to five stacks of ten bars each. Cylindrical lenses in the external cavity allow the magnifications of the fast and slow axes to be separately optimized. Fast axis magnification was chosen at M=20, allowing spectral linewidth on single emitters as low as 30pm. Alignment of the diode elements, splitters, step mirror, and other external cavity elements will determine overall system linewidth and efficiency. We report data from our 3kW prototype and discuss its scalability to several tens of kilowatts.
9729-3, Session 1
(Invited Paper)
Boris D . Barmashenko, Ilya Auslender, Eyal Yacoby, Karol
Waichman, Oren Sadot, Salman Rosenwaks, Ben-Gurion
Univ . of the Negev (Israel)
Modeling of static and flowing gas subsonic, transonic and supersonic Cs and K diode pumped alkali lasers is reported. A simple optical model of
K DPAL applied to the highly efficient static, pulsed K DPAL [Zhdanov et al, Optics Express 22, 17266 (2014)], shows good agreement between the calculated and measured dependence of the laser power on the incident pump power. The model reproduces the observed threshold pump power,
22 W, which is much higher than that predicted by standard models of the
DPAL. The reason for the large values of the threshold power is that the volume occupied by the excited K atoms contributing to the spontaneous emission is much larger than the volumes of the pump and laser beams in the laser cell, resulting in large energy losses due to the spontaneous emission. 3D CFD modeling of subsonic (Mach number M ~ 0.2) and
9729-5, Session 1
Andrey E . Mironov, James G . Eden, Univ . of Illinois at
Urbana-Champaign (United States); William Goldshlag,
University of Illinois at Urbana-Champaign (United States)
Excimer-pumped alkali lasers (XPALs) represent pumping configuration for alkali-atomic lasers that serves as an alternative to classical diode pumped alkali lasers (DPALs). The population inversion in XPALs is achieved by the photoassociation of ground state alkali-rare gas molecules via the blue satellite of the alkali D2 line. The original XPAL pumping scheme provides a broad pump acceptance spectrum (~ 2 nm) and high quantum efficiency
(>95%). However, due to the low absorption cross section normally associated with an alkali-rare gas blue satellite, the original XPAL scheme generally suffers from poor utilization of the pump energy.
We report here a novel pumping scheme for XPALs in which the alkali-noble gas mixtures are pumped with two colors, resulting in greater efficiency and an order of magnitude increase in the pump absorption coefficient. Our
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Conference 9729: High Energy/Average Power Lasers and Intense Beam Applications IX experiments show that synchronous pumping of alkali-noble gas mixtures results in an increase in the overall laser efficiency by at least a factor of
1.7. Also, the effective quantum efficiency of the system is above 100% due to the extraction of 102 cm^-1 of thermal energy per emitted photon. This pumping scheme appears to be applicable to a broad range of alkali-rare gas mixtures. The spectroscopy and kinetics of this new family of lasers will be discussed.
9729-8, Session 1
Valeriy N . Azyazov, Aleksei P . Torbin, Samara State
Aerospace Univ . (Russian Federation); Alexander M . Mebel,
Florida International Univ . (United States); Sean Bresler,
Michael C . Heaven, Emory Univ . (United States) 9729-6, Session 1
(Invited Paper)
Masamori Endo, Tokai Univ . (Japan); Ryuji Nagaoka,
Hiroki Nagaoka, Toru Nagai, Fumio Wani, Kawasaki Heavy
Industries, Ltd . (Japan)
A numerical simulation code of diode pumped alkali laser (DPAL) is developed. We have been observing the output power rollover in our
Cs DPAL, when Cs partial pressure increases, despite the pump power absorption is better. We expect that a detailed simulation code, considering spatial mode overlap and spectral divergence of the pump light could identify the reason of the problem. The code employs the Fresnel-Kirchhoff diffraction integral for both laser mode and pump light propagations between the resonator mirrors. A three-dimensional atomic-photon rate equations are calculated simultaneously to determine the three-dimensional local gain. Spectral divergence of the pump source is represented by a series of (typically 21) pump lights with different wavelengths, occupying the same volume. Stimulated emission and absorption are calculated for these lines with different cross sections determined by the pressure broadening of the Cs atom. The developed simulation is tested for various operational condition of our small-scale (6.5W) DPAL apparatus. Excellent agreement has been seen in most of the tests. Especially, the agreement of the output power dependence on the focal position of the pump light proves the adequacy of the model. Finally, the roll over the output power has been correctly reproduced. It has been found that the main channel of the pump power drain is the spontaneous emission from the upper level of lasing transition, due to the fairly short (35 ns) life time.
Optically pumped alkali vapor lasers commonly use methane (CH4) or ethane (C2H6) as the agent to induce energy transfer between the optically pumped level (n2P3/2) and the upper laser level (n2P1/2). A complication with this scheme is that the alkali metal eventually reacts with the hydrocarbons, yielding particulate carbon and metal hydrides as contaminants in the gain medium. The reactions of ground state alkali metals with methane and ethane are endothermic, but excitation to the first excited 2P state is sufficient to make the reactions slightly exothermic. This is experimentally verified for the related reaction M(2P)+H2 ? MH + H, and thermodynamic data predict that the reactions of M(2P) with methane and ethane will also be exothermic. We have used laser pump-probe methods to examine the reactions of Rb(n2P) with H2, CH4, and C2H6 for states with n=5, 6, and 7. The H2 reactions were examined to validate the LIF method used for RbH detection. For methane and ethane, pump-probe measurements that examined the Rb(5s) ground state recovery kinetics indicated loss due to reaction following pulsed excitation to the n2P states.
Surprisingly, the RbH product was not detected. The results from highlevel ab initio calculations are being used to study the reactive interactions between Rb, methane and ethane.
9729-9, Session 1
(Invited Paper)
James A . Horkovich, Directed Energy Professional Society
(United States)
9729-7, Session 1
Michael Shaffer, Boris V . Zhdanov, Matthew Rotondaro,
Randall Knize, U .S . Air Force Academy (United States)
This talk presents the results of experiments on the direct measurement of the ionization rates in an operating continuous wave static Cs DPAL.
Ionization occurs due several possible mechanisms including multiphoton processes. In these experiments, stainless steel electrodes were mounted inside the lasing alkali cell and biased by the external voltage source.
The collected currents, estimated to be in the nanoampere range, were measured by a PicoAmmeter. We designed and manufactured an alkali vapor cell with AR coated windows and mounted the electrodes inside the cell such that they are parallel to the optical axis of the laser cavity and to the direction of the pump and lasing beams (longitudinal pumping design).
The alkali cell was filled with 1 g of metallic Cs and Methane buffer gas at
600 Torr. The cell was temperature controlled and the vapor density was 1.5 x 1013 cm-3. In these experiments, we have collected data for total ionization current as a function of applied bias voltage across the electrodes for different values of incident resonant pump power in the range 3W – 20W with a maximum output laser power about 10W. These values of ionization currents were converted into total ionization rates and compared to values calculated in previous publications.
This talk presents a history of missile defense and the “Star Wars” program and its’ evolution to today’s tactical battlefield laser systems, marking the
30th anniversary of President Ronald Reagan’s “Star Wars” speech. Since
Archimedes’ “Burning Glass” at the siege of Syracuse 212 B.C. through the development of the LASER man has been fascinated with the idea of using directed energy weapons. But nothing did more to focus this effort than the threat posed by Mutually Assured Destruction. Under Reagan’s
“Star Wars” plan years and billions of dollars were invested in making high energy laser systems a reality. This presentation discusses the fundamentals of laser physics and traces the development of these systems in the USA and USSR from the Gas Dynamic LASER laboratory in the 1960s and the
USAF Airborne Laser Laboratory of 1981 through the SDI era and up to today. In reflecting on the effort invested in developing this technology, this interdisciplinary talk addresses the role that this technology played in changing the geopolitical state of the cold war and continues to play in international defense efforts today. Note: This talk takes 45 – 50 minutes in its complete form. It is most suited as a plenary or historical talk,
9729-10, Session 2
Wilson T . Rawlins, Kristin L . Galbally-Kinney, Steven J .
Davis, Physical Sciences Inc . (United States); Alan R .
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Conference 9729: High Energy/Average Power Lasers and Intense Beam Applications IX
Hoskinson, Jeffrey A . Hopwood, Tufts Univ . (United States)
The optically pumped rare-gas metastable laser is a chemically inert analogue to diode-pumped alkali (DPAL) and alkali-exciplex (XPAL) laser systems. Scaling of these devices requires efficient generation of electronically excited metastable atoms in a continuous-wave electric discharge in flowing gas mixtures at elevated pressure. This paper describes on-going investigations of the use of linear microwave micro-discharge arrays to generate metastable rare-gas atoms at atmospheric pressure in optical pump-and-probe experiments for laser development. Each array consists of a set of microstrip transmission line resonators with a small
(25-100 micron) gap to ground in which the microplasma is ignited. Power requirements to ignite and sustain the plasma at 1 atm are low, <30 W. We report on the micro-discharge excitation and optical pumping dynamics of argon metastables, Ar (4s, 1s5) (Paschen notation), generated in flowing mixtures of Ar and He from 20 Torr to 1 atm. Ar(1s5) concentrations, optically pumped gain, and absorption linewidths are determined by diode laser absorption; Ar(4p) population distributions are determined by laserinduced fluorescence excitation spectroscopy. We observe optically pumped excitation of the 1s5 ? 2p9 transition at 811.5 nm and the corresponding optical gain and lasing action on the 2p10 ? 1s5 transition at 912.3 nm, where the 2p10 state is populated by collisional energy transfer from 2p9. We will present systematic observations of parametric behavior with pressure, gas flow conditions, and micro-discharge geometry and power. We will discuss considerations and expectations for scaling the optically pumped microdischarge to higher output powers.
9729-11, Session 2
Greg A . Pitz, Air Force Research Lab . (United States)
9729-13, Session 2
Pavel A . Mikheyev, Samara State Aerospace Univ . (Russian
Federation); Alexander K . Churnyshov, Nikolay I . Ufimtsev,
P .N . Lebedev Physical Institute (Russian Federation); Anna
R Ghildina, Samara State Aerospace University (Russian
Federation); Valeriy N . Azyazov, Samara State Aerospace
Univ . (Russian Federation); Michael C . Heaven, Emory Univ .
(United States)
Optically pumped all-rare-gas laser (OPRGL) with unique properties comparable to a diode pumped alkali laser (DPAL) was recently proposed.
To study this promising laser system it is necessary to have reliable diagnostics for the active medium. Pressure broadening coefficients, for both self- and foreign-gas collision partners, are needed for spectroscopic measurements of number densities and temperatures in rare gas discharge plasma. However, a literature search shows that pressure broadening coefficients for rare gas lines for mixtures that are of interest for the OPRGL are surprisingly hard to find. Diode laser absorption spectroscopy was employed for measurements of pressure broadening coefficients for krypton in an RF discharge. A MQW-diode laser (L808P030, Thorlabs) with a short external cavity was used as the source of probe radiation. The natural isotopic distribution of Kr was taken into account, and an appropriate fit function was constructed to facilitate determination of the pressure broadening coefficients. The broadening coefficients for the Kr 811.3 nm line atto 300 K were: ?Kr Kr = (2.4 ± 0.2) ?10 10 s 1cm3 for self-broadening and
?Kr He = (3.1 ± 0.2) ?10. 10 s 1cm3 for broadening by helium.
The Advanced Noble Gas Laser (ANGL) uses a mild RF discharge to excite argon (Ar) atoms from the ground state (s0) to the metastable s5 state, allowing Ar to be optically pumped (s5 – p9) as a quasi-three level laser similar to the Diode Pumped Alkali Laser (DPAL). Helium (He) collisional mixing from the p9 to the p10 state allows lasing from p10 to s5 at 912 nm.
Previously, 2 mW of average output power has been achieved at the Air
Force Research Laboratory (AFRL) using a 811 nm pulsed Titanium:Sapphire
(Ti:Sapph) laser to pump a plasma discharge tube with a 1-10% Ar:He mixture. Recently, number density and gain diagnostics have been conducted in a parallel-plate discharge configuration. This architecture was also used in demonstrating the world’s first continuous wave (cw) diodepumped ANGL.
9729-14, Session 2
Jun Gao, Wuhan National Lab . for Optoelectronics (China);
Bin Li, Xinbing Wang, Huazhong Univ . of Science and
Technology (China); Duluo Zuo, Wuhan National Lab . for
Optoelectronics (China) and Huazhong Univ . of Science and Technology (China)
9729-12, Session 2
Jiande Han, Michael C . Heaven, Emory Univ . (United
States); William F . Bailey, Daniel J . Emmons, Glen P .
Perram, Air Force Institute of Technology (United States)
The production of relatively high densities of Ar* metastables (>10e12 cm-3) in Ar/He mixtures, at total pressures close to 1 atm, is essential for the efficient operation of an optically pumped Ar* laser. We have used emission spectroscopy and diode laser absorption measurements to observe the production and decay of Ar* in a parallel plate pulsed discharge.
With discharge pulses of 1 ?s duration we find that metastable production is dominated by processes occurring within the first 100 ns of the gas break-down. Application of multiple, closely spaced discharge pulses yields insights concerning conditions that favor metastable production.
This information has been combined with time-resolved measurements of voltage and current. The experimental results and preliminary model of the discharge kinetics will be presented.
The optically pumped metastable rare gas laser (OPRGL) has attracted more and more attention for its potential to obtain high power laser with good beam quality and atmospheric transmittance. Among all of the rare gases, argon is the cheapest one and the OPRGL using it will be easily conducive to large-scale applications. As the absorption line is an atomic one, the first step for the high power OPRGL of argon is to realize a high power pump source with narrow spectral width emitting around 811.53 nm.
Diode laser pump source for OPRGL of argon was realized by employing a complex external cavity coupled with volume Bragg grating (VBG). A commercial available c-mount LD with rated power of 6 W was used.
The LD were studied in both the free running mode and VBG external cavity. For the external cavity laser diode, the output beam of LD was collimated by an aspherical lens, and the temperatures of VBG and LD were controlled separately by thermal-electrical-coolers (TEC). A high resolution spectrometer with resolution limit 13 pm near 812 nm was applied to measure the spectra of the output laser beam. Maximum output power of 3.9 W with FWHM less than 25 pm and peak wavelength located around
811.53 nm was obtained. The peak wavelength could be tuned more than
300 pm by precise control of the VBG temperature. These results will benefit the further research on OPRGL of argon.
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9729-15, Session 3
Conference 9729: High Energy/Average Power Lasers and Intense Beam Applications IX
Jensen, General Atomics Aeronautical Systems, Inc .
(United States)
Marsel V . Zagidullin, P .N . Lebedev Physical Institute
(Russian Federation); Mikhail S . Malyshev, Samara State
Aerospace Univ . (Russian Federation); Valeriy N . Azyazov,
Samara State Aerospace Univ . (Russian Federation);
Michael C . Heaven, Emory Univ . (United States)
The kinetics of the processes in an O2 – I2 – He – H2O gas flow that is irradiated simultaneously by light at wavelengths near 500 nm and 1315 nm, is considered. Radiation at 500 nm is used to photodissociate about 1% of iodine molecules. The radiation at 1315 nm excites atomic iodine to the
2P1/2 state. Singlet oxygen molecules are produced via the energy exchange process I(2P1/2)+O2(3?) ? I(2P3/2) + O2(1?), while I(2P1/2)+O2(1?) energy pooling produces oxygen molecules in 1? state. I(2P1/2) and O2(1?) then accelerate the dissociation of I2. A kinetic analysis was performed for a gas flow at 70 torr pressure, 300 K temperature, 60 W/cm2 500 nm light intensity and 5 kW/cm2 IR irradiation. It is shown that this scheme produces an oxygen – iodine medium with a high degree of iodine dissociation and a relative content of singlet oxygen O2(a1?) exceeding 10 %. Having formed a supersonic gas flow with a temperature ~100 K from this medium, one can reach a small-signal gain of about 10–2 cm–1 on the 2P1/2 – 2P3/2 transition in iodine atoms. The specific power per unit flow cross section in the oxygen
– iodine laser with this active medium may reach ~100 W cm–2 at an optical efficiency of 60%. If H2O is excluded, which is an active O2(1?) quencher, it is possible to achieve an O2(1?) fraction of up to 70% and inversion of the oxygen b1?=>X3? transition.
We report on investigation of novel 2µ m thulium (Tm)–based laser accelerator driver (LAD) offering efficient generation of high-energy pulses with high-peak power at high repletion rate, high efficiency, and with neardiffraction-limited beam quality (BQ). Laser accelerators of nuclear particles by ultrashortpulse laser-generated plasmas offers much reduced size and cost compared to conventional accelerators of the same energy, which would drastically cut the cost of high-energy particle research on colliderbased facilities and advanced light sources, thus replacing the traditional mammoth-size and costly accelerator research facilities with room-size systems [1].
LAD operating at 2 µ m wavelength offers ponderomotive force 4x that of 1
µ m and 6x that of the traditional 0.8 ?m LAD. In addition, the Tm bandwidth of nearly 400 nm offers >15% tunability and generation of ultrashort pulses down to <30 fs. The “2-for-1” pump architecture of Tm ion enables >20% wall-plug efficiency.
This work presents the relative performance of several Tm-doped materials and LAD configurations.
Comparisons to traditional 0.8µ m Ti-sapphire and 1µ m Yb lasers are also shown. Experimental data on gain uniformity and thermo-optical distortions are presented. This work was in-part supported by the US Department of
Energy Grant Number DE- SC0013762.
1. Proc. of Workshop on Laser Technology for Accelerators, Summary
Report, US Department of Energy, January 23-25, 2013
9729-16, Session 3
Pavel A . Mikheyev, Samara State Aerospace Univ . (Russian
Federation); Nikolay I . Ufimtsev, P .N . Lebedev Physical
Institute (Russian Federation); Andrey V . Demyanov,
Troitsk Institute for Innovation and Fusion Research
(Russian Federation); Igor V . Kochetov, Valeriy N . Azyazov,
P .N . Lebedev Physical Institute (Russian Federation);
Anatoly P . Napartovich, Troitsk Institute for Innovation and
Fusion Research (Russian Federation); Michael C . Heaven,
Emory Univ . (United States)
Experiments and modeling of CH3I dissociation in the plasma of a 40 MHz
RF discharge were performed. A discharge chamber of an original design, consisting of quartz tubes between two planar electrodes, produced iodine atoms at number densities up to 2?1016 cm 3. Contamination of the walls of the tubes did not impair the discharge stability, providing a good iodine production rate. Addition of oxygen into the Ar:CH3I mixture resulted in a substantial increase in CH3I dissociation efficiency. At a discharge power
200 W, complete CH3I dissociation in Ar:CH3I:O2 mixture was observed. The fraction of discharge power spent on iodine atom production at 0.17 mmol/s
CH3I flow rate was 16%. Modeling showed satisfactory agreement with the experiments.
9729-19, Session 4
Mutiu F . Erinosho, Esther T . Akinlabi, Univ . of Johannesburg
(South Africa)
The excellent biocompatibility property of Grade 5 titanium alloy has made its desirability largely increasing in the field of biomedical. The titanium alloy (Ti6Al4V) was modified with the addition of 3 weight percent (wt
%) copper via a laser deposition process using the Ytterbium fiber laser with a wavelength of 1.047 µ m. Therefore, this paper presents the effect of laser power on the microstructural behaviour and strength of the modified
Ti6Al4V+Cu alloy. The laser powers were varied between 600 W and 1600
W respectively while all other parameters such as the scanning speed, powder flow rates and gas flow rates were kept constant. The melt pool and width of the deposited alloy increases as the laser power was increased.
The ?-lamella was observed to be finer at low laser power, and towards the fusion zone, Widmanstettan structures were fused and become smaller; and showing an evidence of ?-martensite phases. The strength of the modified alloy was derived from the hardness values. The strength was observed to increase initially to a point as the laser power increases and afterwards decreased as the laser power was further increased. The improved
Ti6Al4V+Cu alloy can be anticipated for biomedical application.
9729-18, Session 4
Drew A . Copeland, John Vetrovec, Amardeep S . Litt,
Aqwest, LLC (United States); Joseph M . Fukumoto, Steven
9729-20, Session 4
Yang Liu, Zhaojun Liu, Sasa Zhang, Jinbao Xia, Yanmin
Zhang, Chen Guan, Shandong Univ . (China)
Diode-pumped CW and passively Q-switched lasers of Nd:GdLuAG mixed garnet at 1123 nm were demonstrated. The maximum average output power of CW operation was 4.13 W. For Q-switched operation, the average output
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power was 800 mW, the corresponding single pulse energy was 133.8 µ J.
The Nd:GdLuAG laser emitting at 1123 nm was obtained for the first time to the best of our knowledge, which proves that the Nd:GdLuAG mixed garnet has a better ability of energy storage than Nd:YAG in 1123 nm oscillation.
9729-21, Session PTue
Conference 9729: High Energy/Average Power Lasers and Intense Beam Applications IX
Alexsandr S . Grishkanich, Aleksandr Zhevlakov, Sergey
Kascheev, ITMO Univ . (Russian Federation); Igor Sidorov,
Univ . of Eastern Finland (Finland); Valentin Elizarov, ITMO
Univ . (Russian Federation); Andrey Mak, National Research
Univ ITMO (Russian Federation)
9729-22, Session PTue
Vadim V . Kiyko, A . M . Prokhorov General Physics Institute of the Russian Academy of Sciences (Russian Federation) and ITMO Univ . (Russian Federation); Danil Mikhaylov,
A . M . Prokhorov General Physics Institute of the Russian
Academy of Sciences (Russian Federation)
Over the past 10 years the rate of temperature in the Siberia increases almost twice higher than the average rate of warming of the planet.
Identifying methane anomalies responsible for the temperature increase, by hiking trails in the Arctic requires great human labor. It is necessary to use lidar methods for search and identification of methane from permafrost. Necessary to create a Raman lidar for monitoring of emissions of methane hydrate from the permafrost. Hyperspectral resolution would resolve the isotope shifts in the Stokes spectra, thereby to determine the isotopic composition of methane ratio C14/C12 CH4 carbon emissions and identify the source for study (permafrost or oil deposits) Isotopic composition of the methane (concentration of 13C, 14C and D) can provide information concerning the methane origin and formation time. Analysis of the concentration of radioactive isotope 14C allows discerning methane fractions with biological and abiological origins. Isotope 14C appears in the atmosphere due to the cosmic rays. The interaction of nitrogen 14N nuclei with neutrons from the cosmic rays transforms them into the 14C isotope nuclei. Half life of the 14C isotope is 5 730 years, which is significantly exceeds lifetime of absolute majority of Earth life forms. Later on radioactive carbon nuclei emit electron and once again become a stable isotopes 14N.
Carbon isotope 14C interacts with the atmospheric oxygen by forming molecules of carbon dioxide 14CO2. Later these molecules along with the ones of the stable carbon isotope 12CO2 are included into the processes of the living organic matter formation trough the photosynthesis. Automated airborne lidar will allow estimation of the methane emissions intensity, as well as evaluation of qualitative and quantitative parameters of of the methane anomalies.
A modified theoretical model of CO2 laser supplemend with selfinjection of laser output irradiation to unstable cavity is presented. It is based on classical one-dimensional six-temperature model. The model is supplemented with terms that consider influence from self-injected irradiation by external optical system that selects and returns portion of output irradiation. The self-injection influence on static and dynamic parameters of laser system was studied. Also, the dynamic of lasing with temporal modulated self-injection was studied.
It is shown that returning even small part of the output irradiation and its amplification in an active medium radically changes dynamic parameters of laser. It is demonstrated that with temporal modulation of self-injection it is possible to obtain the lasing mode similar to Q-switch by output parameters
(like as pulse shape and duration). Despite similar output parameters, dynamical processes in laser cavity in Q-switched mode and temporal modulated self-injected mode are completely different.
A significant influence on the output characteristics of the laser can be obtained by controlling power an order of magnitude less than the output power of the laser. For example, the numerical simulation showed that with self-injecting power near 5% of laser output power could be obtained the pulse-periodical lasing mode with pulse duration near 300 ns, pulse repetitive rate 20 kHz and peak-to-average power relation near 20. The numerical results have been experimentally verified. During the experiments the lasing mode was changed from CW to pulse-periodical with parameters close to mentioned above with temporal modulated self-injection only.
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9730-1, Session 1
µ
(Invited
Paper)
Gary Stevens, Tom Legg, Gooch & Housego (Torquay)
Ltd . (United Kingdom); Peter Shardlow, ORC, University of
Southampton (United Kingdom)
In this presentation, an overview of the EU FP7 project ISLA (Integrated disruptive componentS for 2 µ m fibre Lasers) is given. The aim of ISLA was to develop a set of “building block” components and a “tool-kit” of processes to define an integrated modular common platform for two micron fibre lasers consisting of compatible and self-consistent active and passive fibres, fused fibre couplers and combiners, fibre-coupled isolators, modulators and high power pump laser diodes.
We also present results from our work on developing passive components for 2 µ m fibre lasers. This includes high power pump combiners that have been tested up to 0.5 kW and combiners for in-band pumping of holmium lasers. Couplers for use as splitters, power monitors and wavelength division multiplexers have also been demonstrated. Wide-band couplers, with a coupling ratio that only varies ± 12% over 400 nm, have also been developed to exploit the wide tuning range possible with thulium fibre lasers.
Research into different isolator materials was also conducted to find materials with large Verdet constants to be used in 2 µ m isolators. Fibrecoupled isolators were then manufactured using a selection of these materials. Isolators that had insertion losses of < 1 dB and isolation of > 35 dB were demonstrated using PM and non-PM fibres. In the PM isolators, PER
> 23 dB was achieved.
9730-2, Session 1
µ
Jon D . Ward, Gooch & Housego PLC (United Kingdom);
Gary Stevens, Gooch & Housego (Torquay) Ltd . (United
Kingdom); Peter C . Shardlow, Univ . of Southampton
(United Kingdom)
Fibre lasers operating in the 2 µ m region are of increasing interest for a range of applications, including laser machining and biomedical systems.
Fibre laser manufacturers were able to call upon enabling technologies used by the telecoms industry when developing lasers at 1 µ m & 1·5 µ m, but at longer wavelengths, for example 2 µ m, many such components are either unavailable or immature.
We report on recent developments of Acousto-Optic Modulators/
Frequency-Shifters and Tunable Filters that are specifically optimised for use with fibre systems operating at or around 2 µ m. AO devices are interesting due their ability to conserve spatial-coherence making them appropriate for use with single-mode optical fibres. We describe how choice of interaction medium is an important consideration, particularly affecting the drive power and the polarisation behaviour of the device – the latter being an important parameter when used in a fibre system.
We also describe two designs of AO Tunable Filter intended for laser tuning.
Both designs have been demonstrated intracavity in 2 µ m fibre lasers. The first gives exceptionally narrow resolution (??/?<0·1%). The second design is of a novel type of AOTF where a matched pair of AOTFs is configured to give a substantially net zero frequency-shift with very little or no loss of pointing stability, any minor deviations in manufacture being selfcompensated. Furthermore, small controlled frequency-shifts (up to about
10kHz) may be introduced with little or no detriment to the alignment of the system.
9730-3, Session 1
Kangpeng Wang, Aidan Baker-Murray, Werner J . Blau,
Trinity College Dublin (Ireland)
Intracavity saturable absorbers are required for passive modelocking. By attaching the saturable absorber to one of the laser resonator mirrors, a saturable absorber mirror (SAM) device is formed.
Saturable absorbers used in the past were typically organic dyes, which suffer from short lifetimes, toxicity, and complicated handling, limiting their application to mostly laboratory systems. Alternative solid-state saturable absorbers include crystals such as Cr:YAG, which typically operate for only limited ranges of wavelengths, recovery times and saturation levels.
Semiconductor saturable absorber mirrors (SESAMs) currently dominate the market. However, these have a narrow tuning range (tens of nanometres), limited product lifetime and require complex fabrication and packaging.
Novel nonlinear materials with broadband absorption are therefore required for wideband tuneable operation and for new upcoming wavelength bands.
Graphene is currently at the centre of a significant global research effort.
Its electronic and mechanical properties are ideal for micromechanical systems, thin-film transistors, and transparent and conductive composites and electrodes. Here, we exploit the optoelectronic properties of graphene for the ultrafast laser market. Pauli blocking following intense illumination results in saturable absorption, independent of wavelength. This effect may be used to passively modelock almost any laser in the visible, near- and mid-infrared region of the electromagnetic spectrum, paving the way to graphene-based photonics.
As part of the FP7 project ISLA, Graphene SAMs were fabricated by a simple wet deposition process onto a metal mirror substrate. Their intensity response was tested at various infrared wavelengths in a so-called i-scan set-up. The results obtained were compared directly with a commercially obtained SESAM from BATOP. The figure below clearly shows saturable absorption with a response that is at least comparable, if not better than the
SESAM.
Particularly the rapidly expanding 2 µ m wavelength range has huge commercial potential as it is of special importance for applications, such as gas detection, including long-range LIDAR applications, free-space optical communication, medical diagnostics, laser surgery, optical pumping of longer wavelength solid-state lasers, material processing and security applications. Hence, the broad-band applicability of our Graphene SAM represents a major market advantage with significant commercial prospects.
9730-4, Session 1
Peter C . Shardlow, Deepak Jain, Richard Parker, Jayanta K .
Sahu, W . Andrew Clarkson, Univ . of Southampton (United
Kingdom)
Two-micron lasers are of great interest for a range of applications, from spectroscopy to polymer machining and laser surgery, as well as being an important stepping stone for wavelength generation further into the
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Conference 9730:
Components and Packaging for Laser Systems II mid infra-red band via nonlinear frequency conversion. Tm-doped silica fibre lasers are especially attractive as they are capable of operating at wavelengths from below 1700nm to more than 2100nm, and can be pumped by commercially available high power laser diodes operating around
~793nm. Moreover, by optimising the dopant concentration within the Tm fibre core a beneficial two-for-one cross-relaxation process can be exploited allowing efficiencies far-above the quantum limit for 793nm pumped Tm fibre lasers. Indeed, efforts to optimise the core composition to enhance this process have been the subject of many studies, but as yet the best slope efficiencies reported for high power cladding-pumped Tm doped silica fibre lasers remain well below the theoretical maximum (~80%). Here we report on our recent Tm fibre development work targeted at improving the twofor-one cross-relaxation efficiency through optimising core composition and doping profiles. Using a fibre with a Tm concentration of 3.6 wt.% yielded a slope efficiency with respect to absorbed pump power of ~70% and with power levels up to 100W, limited by available pump power. Further studies indicate that efficiencies close to the theoretical limit of ~80% should be achievable with the appropriate core design.
Feedback Quantum Cascade Laser (DFB-QCL). The geometrical design and polarization properties have been defined using numerical simulations. A non-symmetric chalcogenide MOF has been realized by taking into account the theoretical results. Finally, the fiber properties have been evaluated using a DFB-QCL emitting at 7.4 µ m and the polarization maintaining at the output of the chalcogenide fiber has been demonstrated .
The combination between a DFB-QCL with such non-conventional fiber has led to the development of the first single-mode polarized fibered Mid IR laser emitting at 7.4
µ m.
9730-7, Session 2
Gary Stevens, Toby Woodbridge, Gooch & Housego
(Torquay) Ltd . (United Kingdom)
9730-5, Session 2
Vadim Smirnov, OptiGrate Corp . (United States); Alex
Sincore, Joshua Bradford, Lawrence Shah, Martin
Richardson, CREOL, The College of Optics and Photonics,
Univ . of Central Florida (United States); Oleksiy Mokhun,
Alexei L . Glebov, OptiGrate Corp . (United States); Leonid
Glebov, CREOL, The College of Optics and Photonics, Univ . of Central Florida (United States) and OptiGrate Corp .
(United States)
Volume Bragg Gratings (VBGs) in photo-thermo-refractive glass have outstanding properties in 2-micron spectral region providing extremely high spectral and angular selectivity, diffraction efficiency up to 99.99%, controlled chirp dispersion, wavelength multiplexing capability, etc. The unique VBG properties enable their use in 2-micron lasers as output couplers, end-mirrors, spectral and angular selectors, stretchers and compressors of ultra-short pulses, spectral beam combiners, notch, bandpass, and spatial filters. This paper reviews recent VBG technology developments as well as various results on VBG applications that can lead to major improvements of fiber, solid-state, and diode laser system performance in 2-micron spectral range.
We present results from our recent efforts on developing single-mode fused couplers in ZBLAN fibre. We have developed a custom fusion workstation for working with lower melting temperature fibres, such as ZBLAN and chalcogenide fibres. Our workstation uses a precisely controlled electrical heater designed to operate at temperatures between 100 – 250oC as our heat source. The heated region of the fibers was also placed in an inert atmosphere to avoid the formation of microcrystal inclusions during fusion.
We firstly developed a process for pulling adiabatic tapers in 6/125 ?m
ZBLAN fibre. The tapers were measured actively during manufacture using a 2000 nm source. The process was automated so that the heater temperature and motor speed automatically adjusted to pull the taper at constant tension. This process was then further developed so that we could fuse and draw two parallel 6/125 ?m ZBLAN fibres, forming a single-mode coupler. Low ratio couplers (1-10%) that could be used as power monitors were manufactured that had an excess loss of 0.76 dB.
We have also manufactured 50/50 splitters and wavelength division multiplexers (WDMs). However, the excess loss of these devices was typically 2 - 4 dB. The increased losses were due to localised necking and surface defects forming as the tapers were pulled further to achieve a greater coupling ratio.
Initial experiments with chalcogenide fibre have shown that our process can be readily adapted for chalcogenide fibres and we have so far demonstrated adiabatic tapering and fusion of a variety of chalcogenide fibres.
9730-6, Session 2
Céline Caillaud, Univ . de Rennes 1 (France); Clément Gilles, mirSense (France); Laurent Brilland, PERFOS (France) and
SelenOptics (France); Laurent Provino, PERFOS (France);
Mathieu Carras, Mickael Brun, mirSense (France); David
Méchin, PERFOS (France); Johann Troles, Univ . de Rennes
1 (France) and SelenOptics (France)
The mid-infrared molecular fingerprint region has gained great interest in the last decade thanks to development of on-chip semiconductor lasers.
For integrated-optic devices and optical sensors based on interferometric techniques, the polarization state of the transmitted signal must be kept constant. In this context, a low-loss single-mode chalcogenide microstructured optical fiber (MOF) which presents a polarization maintaining has been achieved in order to be connected to a Distributed
9730-8, Session 2
Leo J . Missaggia, Christine A . Wang, Michael K . Connors,
Brian G . Saar, Antonio Sanchez-Rubio, Kevin J . Creedon,
George W . Turner, William Herzog, MIT Lincoln Lab .
(United States)
There are a number of military and commercial applications for high power laser systems in the mid to long infrared wavelength range. By virtue of their demonstrated watt level high power performance and wavelength diversity, quantum cascade (QC) laser and amplifier devices are an excellent choice of emitter for those applications. In order to realize the power levels of interest, beam combining of arrays of these emitters would be required and as a result, array technology must be developed. With this in mind, packaging and thermal management strategies were developed to facilitate the demonstration of a monolithic QCL array operating under CW conditions. Thermal models were constructed and simulations performed to determine the effect of gain region temperature rise on parameters such as array element ridge width, pitch and cavity length. The results of the simulations were considered in determining an appropriate QCL array configuration. State-of-the-art micro-impingement cooling along with an
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Conference 9730:
Components and Packaging for Laser Systems II electrical distribution scheme comprised of AlN multi-layer technology were integrated into the design. The design of the module allows for individual electrical addressability of the array elements, a method of phase control demonstrated previously for coherent beam combining of diode arrays, along with access to both front and rear facets. Hence, both laser and single pass amplifier arrays can be accommodated. A module was realized containing a 5 mm cavity length monolithic QCL array comprised of 7 elements on 450 ?m pitch. An output power of 3.16 W was demonstrated under CW conditions at an emission wavelength of 9 ?m.
Blue-emitting external cavity laser diode.
[1] Wenzel, H., Fricke, J., Klehr, A., Knauer, A., Erbert, G., “High-power 980nm
DFB RW lasers with a narrow vertical far field,” Photon. Technol. Lett. 18,
737–739 (2006).
[2] Klehr, A., Bugge, F., Erbert, G., Fricke, J., Knauer, A., Ressel, P., Wenzel,
H., Trekle, G., “High power broad-area 808nm DFB lasers for pumping solid state lasers,” Proc. SPIE 6133, 61330 (2006).
9730-9, Session 3
Dong Hou, Jingwei Wang, Lijun Gao, Dong Lu, Xingsheng
Liu, Xiaoning Li, Xi’an Focuslight Technologies Co ., Ltd .
(China)
9730-11, Session 3
John Downing, USL Technologies LLC (United States)
The application of high power diode lasers is keep increasing in many fields, including scientific research, aerospace, display and medical applications etc.
The horizontal array of high power diode laser stack is widely used in pumping applications in industry. The spectrum with narrow FWHMand accurate central wavelength of the diode laser stack is required for high absorption efficiency of the pumping crystal in pumping applications.
However, the control of spectrum uniformity of the multiple diode laser stacks is difficult due to the wavelength shift before and after bonding on the heatsink. Thus the precision control of the spectrum is critical in high power diode laser stack development. Soft solder of indium is used to bond laser diode bar onto copper heatsink traditionally, however, the repeated on-off current-cycling in laser operations can cause mechanical stress, which leads to various failures, such as material cracking, migration and thermal fatigue.
In this work, a sophisticated high power and high performance horizontal array (30bars module) of conduction cooled diode laser have been developed. Uniform wavelength with narrow FWHM and accurate central wavelength is obtained through the numerical simulation and wavelength screening of unit stacks of diode laser. The wavelength value of FWHM and
FW 90% energy of 30bars module achieves 2.69nm and 4.39nm in working condition. AuSn bonding technology and CTE-matched submount are applied to acquire high reliability and high output power (6000W in total).
The hard solder bonding technology and spectrum control technology are promising approaches to achieve superior laser performance in industry.
Operating wavelength and beam quality, photodiode responsivity and spatial uniformity, and the properties of beam-forming optics vary systematically with temperature in laser-diode systems. Consequently, temperature is the dominant environmental factor affecting their stability.
The net effect of temperature on optical power stability can be as large as
5,000 ppm/oC. Traditionally, temperature effects have been suppressed by operating laser diodes at constant temperature with thermoelectric coolers
(TECs). While this method is a virtual industry standard in applications such as spectroscopy that require constant wavelength, more than half of the electrical power for system operation can be consumed by the TEC. This paper reports the development of an optical feedback module for stabilizing the output optical power of laser diodes without TECs. It complements prior work on electronic and optical methods for stabilizing VCSEL power.
The optical feedback module comprises a weakly polarizing beamsplitter, a monitor photodiode characterized by low temperature sensitivity (< 10 ppm/oC), highly uniform responsivity (< 100 ppm/mm), and sub 1%-peryear drift configured in an APC circuit. Since the module samples the output laser beam, it provides true closed-loop control that is immune to errors arising from differential aging of the front- and back-facet optical properties. Tests with an inexpensive (<$15), single-mode, 5 mW, red laser diode, which mode hops demonstrate that a system temperature coefficient of 19 ppm/oC can be obtained. This represents a 35-fold improvement in stability over what can be achieved with the internal monitor photodiode.
Measurement systems that require ultra-stable power and high wall-plug efficiency are ideal candidates for the technology so long as they can tolerate wavelength variations in the range from 1.5 nm (blue and green bands) to 15 nm (red and NIR bands) over a 50o C range.
9730-10, Session 3
Hong Man Na, Korea Univ . (Korea, Republic of)
9730-12, Session 4
(Invited Paper)
Robin K . Huang, TeraDiode, Inc . (United States)
Blue-emitting laser diode is required many industrial fields such as medical application, spectroscopy, and measurement techniques. Enhancement of output power with narrow bandwidth is currently one of the important factors for evaluating the laser diode specifications. Although the directemitting blue laser diode is available for the high output power, it has a relatively wide spectral bandwidth and a lack of wavelength stabilization with injection current. The appending of internal grating is one of the possible ways to the enhancement [1.2], but it is still technically challenging due to the difficulties of processing in a blue laser diode. In order to improve both the narrow bandwidth and the high output power simultaneously, one of the most promising methods is to use an external cavity.
In this paper, a blue emitting External cavity laser diode utilizing AR coated broad-area solitary blue laser diode was demonstrated. The high efficient output power, narrow spectral bandwidth, wavelength-locking and wavelength-tuning ability with varying injected currents were investigated in
TeraDiode is manufacturing multi-kW-class ultra-high brightness fibercoupled direct diode lasers for industrial applications. A fiber-coupled direct diode laser with a power level of 4,680 W from a 100 µ m core diameter,
<0.08 numerical aperture (NA) output fiber at a single center wavelength was demonstrated. Our TeraBlade industrial platform achieves worldrecord brightness levels for direct diode lasers. The fiber-coupled output corresponds to a Beam Parameter Product (BPP) of 3.5 mm-mrad and is the lowest BPP multi-kW-class direct diode laser yet reported. This laser is suitable for industrial materials processing applications, including sheet metal cutting and welding. This 4-kW fiber-coupled direct diode laser has comparable brightness to that of industrial fiber lasers and CO2 lasers, and is over 10x brighter than state-of-the-art direct diode lasers.
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Conference 9730:
Components and Packaging for Laser Systems II
9730-13, Session 4
Xiaoning Li, Jingwei Wang, Xi’an Focuslight Technologies
Co ., Ltd . (China); Dong Hou, Xi’an Focuslight Technologies
Inc . (China); Xingsheng Liu, Xi’an Focuslight Technologies
Co ., Ltd . (China)
With the increasing applications of high power semiconductor lasers in industry, advanced manufacturing, aerospace, medical systems, display, entertainment, etc., there is a strong demanding of diode lasers with high power and high reliability. Currently, the typical peak output power of commercially available diode laser is only 150-300W per bar for quasicontinuous wave (QCW) used. The performance of diode laser can be significantly affected by the packaging structure and packaging process.
In this work, a novel micro channel cooler (MCC) for stack array laser with good heat dissipation capacity and high reliability is presented. Numerical simulations on the effects of different MCC structure on the thermal behavior and thermal stress behavior are conducted and analyzed. Based on this new MCC packaging structure, a high power hard solder laser array of
500W has been fabricated. A series of techniques such as spectrum control and smile control have been applied to achieve a narrow spectrum and high beam quality. The performances of the laser array are characterized. A narrow spectrum of 3.17 nm and an excellent smile effect are obtained. The lifetime of the laser array is more than 1.38*10^9 shots and still ongoing.
Today, the precision of micro-optics assembly is mostly limited by the accuracy of the bonding process - and in the case of adhesive bonding by the prediction and compensation of adhesive shrinkage during curing.
In this contribution, we present a novel approach to address adhesive bonding based on hybrid control system theory. In hybrid control, dynamic systems are described as “plants” which produce discrete and/or continuous outputs from given discrete and/or continuous inputs, thus yielding a hybrid state space description of the system. The task of hybrid controllers is to observe the plant and to generate a discrete and/or continuous input sequence that guides or holds the plant in a desired target state region while avoiding invalid or unwanted intermediate states. Our approach is based on a series of experiments carried out in order to analyze, define and decouple the dependencies of adhesive shrinkage on multiple parameters, such as application geometries, fixture forces and UV intensities. As some of the dependencies describe continuous effects (e.g. shrinkage from UV intensity) and other dependencies describe discrete state transitions (e.g. fixture removal during curing), the resulting model of the overall bonding process is a hybrid dynamic system in the general case. For this plant model, we then design and evaluate hybrid controllers with the potential to optimize process control for a selection of assembly steps, thus improving the repeatability of related production steps like beam-shaping optics, mounting of turning mirrors for fiber coupling or building resonators evaluating power, mode characteristics and beam shape.
9730-14, Session 4
Gunnar Böttger, Daniel Weber, Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration (Germany);
Friedemann Scholz, Eagleyard Photonics GmbH
(Germany); Henning Schröder, Martin Schneider-
Ramelow, Fraunhofer-Institut für Zuverlässigkeit und
Mikrointegration (Germany); Klaus-Dieter Lang, Technische
Univ . Berlin (Germany)
Fraunhofer IZM, Technische Universität Berlin and eagleyard Photonics will present various implementations of current micro-optical assemblies for high quality free space laser beam forming and efficient fiber coupling.
The laser modules shown are optimized for fast and automated assembly in small form factor packages via state-of-the-art active alignment machinery, using alignment and joining processes that have been developed and established in various industrial research projects. Operational wavelengths and optical powers ranging from 600 to 1600 nm and from 1 mW to several
W respecitvely will be addressed, for application in high-resolution laser spectroscopy and sensing or laser-medical treatment.
9730-16, Session 4
Jenna Campbell, Freedom Photonics, LLC (United States);
Tadej Semenic, Teledyne Scientific Co . (United States);
Paul O . Leisher, Rose-Hulman Institute of Technology
(United States); Avijit Bhunia, Teledyne Scientific Co .
(United States); Milan Mashanovitch, Daniel Renner,
Freedom Photonics, LLC (United States)
Existing thermal management technologies for diode laser pumps place a significant load on the size, weight and power consumption of High Power
Solid State and Fiber Laser systems, thus making it impossible for these laser systems to be used in many important practical applications. This problem is being addressed by the team formed by Freedom Photonics and
Teledyne Scientific through the development of novel high power laser chip array architectures that can operate at temperatures higher than 50 degrees
Celsius with high efficiency and also the development of an advanced thermal management system for efficient heat extraction from the laser chip array. This paper will present experimental results for the optical, electrical and thermal characteristics of 980 nm diode laser pump modules operating effectively with liquid coolant at a temperature of 50 degrees Celsius, showing a very small change in performance as the operating temperature increases from 20 to 50 degrees Celsius. These pump modules can achieve output power of many Watts per array lasing element with an operating
Wall-Plug-Efficiency (WPE) of 50% and higher, at elevated temperatures.
The paper will also discuss the technical approach that has enabled this high level of pump module performance and opportunities for further improvement.
9730-15, Session 4
Christian Schlette, Institute for Man-Machine Interaction
(Germany); Tobias Müller, Daniel Zontar, Fraunhofer-
Institut für Produktionstechnologie IPT (Germany);
Jürgen Rossmann, Institute for Man-Machine Interaction
(Germany); Christian Brecher, Fraunhofer-Institut für
Produktionstechnologie IPT (Germany)
9730-43, Session PTue
Andrejus Michailovas, EKSPLA uab (Lithuania); Saulius
Frankinas, Nerijus Rusteika, EKSPLA uab (Lithuania) and
Ctr . for Physical Sciences and Technology (Lithuania);
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Vadim Smirnov, Ruslan Vasilyeu, Alexei L . Glebov,
OptiGrate Corp . (United States)
The power scaling of ultrafast fiber laser is restricted due to nonlinear pulse distortion in fiber. Hence sufficient pulse stretching is necessary to reduce pulse peak power and nonlinear effects. To achieve high pulse energy
(~10 µ J) stretched pulse duration is typically in the range of 100ps – 1ns and the physical size of the matched diffraction grating compressor is large. An alternative technology for large-sized diffraction grating compressor is pulse compression based on large aperture chirped volume Bragg grating (CVBG).
In the typical schemes CVBG is used as a pulse stretcher and a compressor, however this configuration requires additional dispersion compensation to eliminate the residual normal dispersion of the fiber. As the dispersion of
CVBG cannot be easily tuned, compensation of the dispersion in the system is cumbersome and requires cutting back some part of the fiber to obtain shortest pulse.
In this work we present a novel chirped pulse amplification (CPA) configuration consisting of chirped fiber Bragg grating (CFBG) with tunable dispersion as pulse stretcher and CVBG as pulse compressor. Both CFBG and CVBG are written with linear chirp profile so that total dispersion of the system, including the fiber, is close to zero. In addition dispersion profile of
CFBG can be fine tuned by inducing thermal gradient along the grating so that an optimization of the duration of the output pulses can be performed.
We demonstrate that using this stretcher/ compressor configuration pulses can be stretched up to 300 ps and compressed to sub-1ps without residual pedestal.
9730-44, Session PTue
Conference 9730:
Components and Packaging for Laser Systems II
Lewis G . Carpenter, Christopher Holmes, Peter A . Cooper,
James C . Gates, Corin B . E . Gawith, Peter G . R . Smith, Univ . of Southampton (United Kingdom)
9730-45, Session PTue
Sebastian Sauer, Sebastian Haag, Tobias Müller, Daniel
Zontar, Christian Brecher, Fraunhofer-Institut für
Produktionstechnologie IPT (Germany)
The assembly of optical components for laser systems is proprietary knowledge and typically done by well-trained personnel in clean room environment as it has major impact on the overall laser performance.
Rising numbers of laser systems drives laser production to industriallevel automation solutions allowing for high volumes by simultaneously ensuring stable quality, lots of variants and low cost. Therefore, an easy programmable, expandable and reconfigurable machine with intuitive and flexible software environment for process configuration is required.
Fraunhofer IPT demonstrated the automated ultra-precise alignment of optical systems in previous publications with an approach to the fully automated assembly. With that expertise on optical assembly processes,
Fraunhofer IPT made the next step towards industrializing the production of optical systems. For these purposes Fraunhofer IPT integrated its micromanipulator technology into an automatic assembly machine and focused on modularizing both mechanical and software components.
The platform war designed and approved to enable laser companies with low expertise and resources in mechanical engineering and industrial control to transfer manual assembly processes to automated or semiautomated processes. Alongside with reduced production costs, higher yields and reduced cycle times company internal process knowledge about measurement setups or alignment strategies as well as bonding remains proprietary. Crucial to enable rapid automation of complex processes by non automation experts is an intuitional software user interface for control development. Furthermore, the laser experts must be capable of integrating well-established laboratory equipment such as measurement systems into the control environment of the industrial production process.
We demonstrate 300 mW level laser power measurements utilising radiation pressure induced microcantilever deflection. Our approach incorporates a channel waveguide within a microcantilever, representing a low cost, fully integrated optomechanical power measurement. This approach has the benefit of fast response times (kHz) in comparison to thermal detectors and we are able to operate our devices over a wider wavelength range (i.e. limited by the reflectivity of gold) than traditional semiconductor detectors.
Our microcantilever devices consist of a reflecting mirror fabricated on a microcantilever; embedded within the cantilever is a channel waveguide with a series of Bragg gratings that can measure cantilever deflection and temperature simultaneously. The ability to interrogate cantilever deflection and temperature allows for the disentanglement of radiation pressure and absorbed light. Cantilever deflection and device temperature can be measured simultaneously by monitoring shifts in Bragg grating central wavelengths by monitoring Bragg gratings in areas of high strain within the cantilever and within bulk areas of the same chip, respectively. In previous demonstrations we have shown mass and temperature sensitivities of 1 µ g and 0.03 °C respectively.
We will present our latest results on the use of these microcantilevers for high sensitivity radiation pressure based power measurements. We are currently investigating the suitability of these devices for measuring beyond watt level laser sources and will discuss the challenges associated with this.
9730-46, Session PTue
Lihe Zheng, Takunori Taira, Institute for Molecular Science
(Japan)
A sub-nanosecond passively Q-switched monolithic green laser with laser-head size of 35 x 35 x 35 mm3 was developed for laser processing on organic superconducting transistor with a flexible substrate. A composite
YAG/Nd:YAG/Cr4+:YAG/YAG crystal was used for generating fundamental wavelength at 1064 nm. The gain medium was a [100]-cut Nd:YAG crystal.
[110]-cut Cr4+:YAG crystal with initial transmission of 30% was used as saturable absorber. Undoped YAG was used as heat sink. The output coupler with transmission of 50% was coated on the end surface of Cr4+:YAG crystal. The stable passively Q-switched 1064 nm laser was operated without additional cooling. A fiber-coupled 806.6 nm, qCW laser diode with output power of 30 W and pump pulse duration of 245 µ s was used. The pump beam was focused into 1.1 mm spot with the help of coupling lenses.
A LBO crystal (? = 90°,?= 11.4°) with size of 5? 5 ? 10 mm3 lead to output energy of 111 µ J, pulse duration of 560.8 ps and peak power of 198kW at
532 nm. A cartridge heater was used to maintain the LBO crystal at fixed temperature of 29.8 ? for second harmonic generation. Further experiments will focus on the angle dependence between [100]-cut Nd:YAG and [110]-cut
Cr:YAG for higher output energy. We acknowledge the support of SENTAN,
JST (Japan Science and Technical Agency) for this work.
78 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9730:
Components and Packaging for Laser Systems II
9730-47, Session PTue
Alexsandr S . Grishkanich, Alexsandr Zhevlakov, ITMO Univ .
(Russian Federation); Egor Gavrilov, Lasers and Optical
Systems, J .S .C . (Russian Federation) and Institute for Laser
Physics (Russian Federation); Sergey Kascheev, ITMO
Univ . (Russian Federation); Veli Kujanpää, VTT Industrial
Systems (Finland); Timo Savinainen, VTT Industrial systems (Finland) and VTT Industrial Systems (Finland) approach for true X/Y scanning at line speeds of 200 meters per second.
Utilizing an innovative approach which incorporates both high speed/ high precision polygon mirrors working in concert with galvanometers, an integrated scan head which accommodates almost all wavelengths at speeds up to 200 meters per second is now possible.
9730-17, Session 5
(Invited Paper)
Andreas Unger, Willhelm Fassbender, Holger Müntz,
Bernd Köhler, Jens Biesenbach, DILAS Diodenlaser GmbH
(Germany)
The divergence value difference in two directions of discharge excimer laser beam reduces the energy concentration in plane of DUV radiation focusing as well as in the image localization plane. The goal of this work was the shaping a laser beam with enhanced homogeneity of intensity distribution in transverse section and the same divergence in two orthogonal directions with respect to the beam axis. An optical attachment designed and manufactured is intended for the DUV laser beam divergence equalization required in the various material micromachining and technologies of surface radiation modification including IC manufacture. KrF laser beam with orthogonal section of 3 x 20 mm and divergence of 2 x 5 mrad has been respectively conversed to one with a square area of 20 x 20 mm and divergence of 5 x 5 mrad.
9730-48, Session PTue
Mohamed Amine Jebali, AFL (United States)
Power scaling of multi-kilowatts fiber laser has been driving the development of glass and fiber processing technology. Designed for large diameter fibers, this technology is used for the fabrication of fiber-based components such as end-pump and side pump combiners, large diameter encaps ,ball lenses for collimators and focusers… The use of 10.6um CO2 lasers as heating element has proven uncomparable flexibility, process control and repeatability when compared to conventional heating methods.
This low maintenance technology provides an accurate, adjustable and uniform heating area by absorption of fused silica of the 10.6m laser radiation. However, commercially available CO2 lasers often experience some power, polarization and mode instability, that becomes important at 20W output power and higher. In the present paper we present a polarization and wavelength insensitive optical feedback control system for stabilizing commercially available CO2 lasers. Less than 1% power fluctuation was achieved at different laser power levels, ranging from as 5 to 40W.
9730-49, Session PTue
Glenn Stutz, Lincoln Laser Co . (United States)
With the recent advent of pulse on demand (PoD) Femtosecond and
Picosecond high speed lasers, industry applications as widespread as medical, industrial and manufacturing are now seeking to take advantages of the economies of scale that these technologies offer. Applications include cataract surgery, high speed printing on plastic packaging, OCT, fine line ablation and cutting and high speed manufacturing processing to name a few.
This presentation provides an overview of the leading edge scan head technology which allows users to implement an integrated total solution
In modern diode lasers beam shaping of the highly asymmetric laser beam, which exits the front facet of the semiconductor laser material, is a crucial step towards cost efficient high brightness laser modules which in turn can be further combined towards kW-class diode lasers and can be efficiently fiber coupled. In order to scale up the power of a single laser module in an economic way, high fill factor laser bars are employed. The increased power density from such a laser bar requires improved cooling technologies. On the other hand the increased fill factor of the bar makes advanced beam shaping necessary to be able to achieve small focal spot sizes and couple the laser module efficiently into optical fibers. Finally, to be able to mass produce the laser modules, it is desirable to design the module in a way that allows automated packaging and optics alignment.
In this talk, the beam shaping concepts developed at DILAS for high fill factor bars are presented. Starting from optical simulation and choice of optical elements the laser modules incorporating these bars are presented.
The concepts developed enable very compact laser modules of up to 2kW of power at a single wavelength with beam qualities of less than 40mm x mrad. Optionally these modules can be wavelength stabilized via external feedback. The packaging technology developed enables the automated alignment of the optics and cooling is DI-water free. Based on the same concepts very compact free space and fiber coupled QCW packages are presented as well.
9730-18, Session 5
µ
Xiaochen Jiang, Rui Liu, Yanyan Gao, Tujia Zhang,
Xiaoguang He, Jing Zhu, Qiang Zhang, Thomas C . Yang,
Cuipeng Zhang, BWT Beijing Ltd . (China)
Fiber coupled diode lasers are widely used in many fields now especially as pumps in fiber laser systems. In many fiber laser applications, high brightness pumps are essential to achieve high brightness fiber lasers.
Furthermore, 976nm wavelength absorption band is narrow with Yb3+ doped fiber lasers which is more challenging for controlling wavelength stabilized in diode laser modules. This study designed and implemented commercial available high brightness and narrow wavelength width lasers to be able to use in previous mentioned applications.
Base on multiple single emitters using spatial and polarization beam combining as well as fiber coupling techniques, we report a wavelength stabilized, 105?m NA 0.15 fiber coupled diode laser package with 100W of optical output power at 976 nm, which are 14 emitters inside each multiple single emitter module. The emitting aperture of the combined lasers output are designed and optimized for coupling light into a 105?m core NA 0.15 fiber. The spectral width is roughly 0.5 nm (FWHM) and the wavelength shift per °C < 0.02nm. The output spectrum is narrowed and wavelength is stabilized using Volume Bragg gratings (VBGs). The high brightness package has an electrical to optical efficiency better than 45% and power enclosure more than 90% within NA 0.12.
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Conference 9730:
Components and Packaging for Laser Systems II
A reliability study has been included on this kind of hermetic package.
Mechanical shock, vibration and accelerated aging tests show that the package is reliability and the MTTF is calculated to be more than 100k hours at 25?.
power out of a 400 µ m fiber and 0.18 NA beam, compared to the current generation elementTM products, while also improving the reliability by an estimated 20%. Additionally, we will report on the improvements in VBG locking, where we have increased the wavelength stabilized range from 6
A for our current generation devices, to a 15 A range for next generation devices.
9730-19, Session 5
Daniel Richter, Christian Voigtländer, Jens U . Thomas,
Ria G . Krämer, Friedrich-Schiller-Univ . Jena (Germany);
Hagen Zimer, TRUMPF Laser GmbH (Germany); Andreas
Tünnermann, Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany) and Friedrich-Schiller-Univ .
Jena (Germany); Stefan Nolte, Friedrich-Schiller-Univ . Jena
(Germany) and Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany)
We report on reducing the power dependent drift of externally stabilized diode lasers emitting around 969 nm by employing ultrashort pulse written
Volume-Bragg-Gratings (VBGs) in fused silica. Spectrally stabilized sources are of special interest for a large variety of applications. One example is the use of high power laser diodes for optical pumping of lasers with a very narrow peak of the absorption cross section. Robust external stabilization of the laser diode source can be obtained using a VBG. Common VBGs are typically written with UV light and post processed into special photothermal-refractive materials. However, these devices suffer from a small residual absorption, which typically leads to a shift of about 200 pm for an optical load change of 50W passing a 10mm2 facet of the grating.
Here we report on applying ultrashort laser pulses and the phase mask scanning technique to directly inscribe VBGs in fused silica. The gratings realized exhibit comparable grating geometries and reflectivities as the conventional VBGs. However, the residual drift of only 20 pm which is one order of magnitude lower and the best value obtained so far to the best of our knowledge. We will present detailed information about the inscription process as well as the grating details and we will outline pathways for even further improvement.
9730-20, Session 5
David M . Hemenway, Ling Bao, Manoj Kanskar, Mark
DeVito, Wolfram Urbanek, Mike P . Grimshaw, Kevin
Bruce, David Dawson, Robert Martinsen, nLIGHT Corp .
(United States); Paul O . Leisher, Rose-Hulman Institute of
Technology (United States)
9730-21, Session 6
(Invited Paper)
Martin E . Fermann, IMRA America, Inc . (United States)
No Abstract Available
9730-22, Session 6
(Invited Paper)
Shih-Chang Wang, Teng-Yi Yang, Dong-Yo Jheng, Chun-
Yang Hsu, Tzu-Te Yang, National Taiwan Univ . (Taiwan);
Pinghui S . Yeh, National Taiwan Univ . of Science and
Technology (Taiwan); Sheng-Lung L . Huang, National
Taiwan Univ . (Taiwan)
Heat dissipation limits the high power performance of various solidstate laser sources. Drawing solid-state gain media into crystalline fibers significantly increases the surface area (for heat removal) to gain volume
(for power generation) ratio. The core diameter can be as small as 3 ?m to tens of microns with high crystallinity. With waveguide structure using glass or ceramic claddings, the mode quality is ensured and the propagation loss is reduced. Various widely used solid-state laser crystals, such as Ti:sapphire and YAGs doped with Ce3+, Yb3+, Cr4+ ions, have been demonstrated as tunable crystalline fiber lasers (> 150-nm tuning range), high slope efficiency
(> 75%), and high-brightness broadband light emitters. The clad-pump scheme used in high power silica fiber lasers have also been applied on crystalline fiber light sources for power scaling and efficient laser diode coupling. The recent advancement on the codrawing laser-heated pedestal growth technique on broadband emissions have shown superiority on the application for optical coherence tomography where broadband, high brightness, CW, and Gaussian spectral shape are preferred for in vivo and real-time diagnosis with cellular resolution.
The challenges on the development of glass/ceramic-clad sapphire and
YAG fibers, including core diameter uniformity, dopant segregation, residual strain, post-growth thermal treatment, and the thermal expansion coefficient mismatch between the crystalline core and glass/ceramic clad, will be addressed in the presentation. The present status on the development of single-mode crystalline fibers using high index glass or ceramic as the fiber clad will also be discussed.
There is an increasing demand for high power diode lasers packages with stabilized wavelengths in the range of 878 nm to 888 nm for DPSS laser pumping applications. In this paper we present nLIGHT’s most recent development of wavelength-stabilized high power, single emitter laser diode packages, elementTM , for DPSS laser pumps. We will report on how we have scaled single emitter power from 10 W per emitter with our prior generation of 200 µ m wide and 3.8 mm long devices to 13 W per emitter for next generation of 5 mm cavity length device for 200 µ m and 0.22 NA fiber products. Furthermore, we will also discuss results for 15 W per emitter devices for 400 um and 0.22 NA fiber products. The improvement in power at the chip-on-submount level results in approximately 50% increase in
9730-23, Session 6
Yu Liu, Hao Yu, Politecnico di Torino (Italy); Alessio
Califano, OPI Photonics s .r .l . (Italy); Andrea Braglia,
Politecnico di Torino (Italy) and OPI Photonics (Italy);
Guido Perrone, Politecnico di Torino (Italy)
Fused fiber combiners are essential components for the realization of alignment free, compact and robust all-fiber systems for communications,
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Conference 9730:
Components and Packaging for Laser Systems II
L . Dallas, Avo Photonics, Inc . (United States) industrial material processing, medicine, sensing, etc. In particular, in high power applications, combiners are used in fiber and direct diode lasers to scale up the power by merging the output of several lower power sources, and this poses stringent requirements on the coupling efficiency and on the acceptable beam quality degradation. This, not only to avoid wasting power, but also to prevent overheating for reliability issues. Moreover, combiners used in different systems, have peculiar requirements and thus necessitate proper tailoring of the design and fabrication procedures.
The usual path to optimize combiner performance is by trial-and-error methods, but this is costly and time-consuming; furthermore, care must be taken in their characterizations since measurements are usually affected by working conditions (e.g. the laser diodes). To help overcoming these drawbacks, we have developed a procedure to predict the efficiency of combiners before manufacturing, therefore allowing the fabrication of high performance devices with reduced experimental optimization costs. The proposed approach is based on statistical analysis applied to ray tracing simulations that takes into account fiber types, geometries, glass material properties and required beam quality. Comparison between predictions and experimental realizations of 7-to-1 and 19-to-1 combiners are given, analyzing the impact of taper length, taper ratio, confining tube material and diode numerical aperture, in both of single- and double-clad delivery fibers.
Tunable Diode Laser Absorption Spectroscopy (TDLAS) has become an industrial-accepted analytical technique for accurate and precise measurement of specific gas components in complex gas mixtures, often laden with liquids or solid particulates. Examples include measuring the moisture content of natural gas within pipelines or in the airflow of heat treatment furnaces, and oxygen content in hydrocarbon vapors such as oil, liquid fuel, and natural gas storage tanks. A key virtue if TDLAS is that the analyte need not contact electrical components; only the low-power laser beam needs to probe the sample. Thus, the technique is suitable for use in potentially explosive hazardous area installations. Particularly useful is the backscatter configuration, wherein the laser beam projects from a transceiver into the sampling area and scatters from a non-cooperative surface within the area. The portion of the scattered light returned to the transceiver contains information from which analyte concentration is deduced.
Emerging applications for this technology, e.g., measuring oxygen in vehicle or aircraft fuel tanks, demand high-volume manufacturing of low-cost, compact and lightweight transceivers. This paper describes the design of such a hermetically-sealed package, occupying a volume less than 1 in3 and weighing less than 0.05 lb. Estimated costs for this critical system component are less than $1000 per unit when produced in lots of 500, approximately a 5x reduction compared to the current state-of-the-art.
9730-24, Session 6
Jens Löhring, Matthias Winzen, Heinrich Faidel, Jörn
Miesner, Heinz-Dieter Plum, Jürgen Klein, Oliver Fitzau,
Martin Giesberts, Wolfgang Brandenburg, Anja Seidel,
Natascha Schwanen, Dana Risters, Hans-Dieter Hoffmann,
Fraunhofer-Institut für Lasertechnik (Germany)
9730-26, Session 7
(Invited
Paper)
Johan Boullet, ALPhANOV (France); Germain Guiraud,
Lab . Photonique, Numérique et Nanosciences (France) and Azur Light Systems (France); Giorgio Santarelli, Lab .
Photonique, Numérique et Nanosciences (France); Cyril
Vincont, Simon Salort, Christophe Pierre, ALPhANOV
(France)
Spaceborne lidar systems have a large potential to become powerful instruments in the field of atmospheric research. Obviously, they have to be in operation for some years without any maintenance like readjusting.
Furthermore, they have to withstand strong temperature cycles typically in the range of -30 to +50 °C as well as mechanical shocks and vibrations, especially during launch. Additionally, the avoidance of any organic material inside the laser box is required, particularly in UV lasers.
For atmospheric research pulses of about several 10 mJ at repetition rates of several 10 Hz are required in many cases. Those parameters are typically addressed by DPSSL that comprise components like: laser crystals, nonlinear crystals in pockels cells, faraday isolators and frequency converters, passive fibers, diode lasers and of course a lot of mirrors and lenses. In particular, some components have strong requirements regarding their tilt stability that is often in the range of <10 µ rad.
In most of the cases components and packages that are used for industrial lasers do not fulfil all those requirements. Thus, the packaging of all these key components has been developed to meet those requirements only making use of metal and ceramics beside the optical component itself. All joints between the optical component and the laser baseplate are soldered or screwed. No clamps or adhesives are used.
Most of the critical properties like tilting after temperature cycling have been proven in several tests. Currently, these components are used to build up first prototypes for spaceborne systems.
9730-25, Session 7
(Invited Paper)
Michael B . Frish, Mathew C . Laderer, Clinton J . Smith,
Physical Sciences Inc . (United States); Ryan Ehid, Joseph
Extreme core dimensions of active photonic crystal fiber (PCF) has increased by one order of magnitude the capabilities of ultrafast fiber lasers: hundred watts of average power, multi-gigawatt of peak power are now delivered by fiber based systems.
Anyway, intrinsic characteristic of PCF make development of fully monolithic architecture extremely challenging: as air holes ensure the guiding properties of the fiber, fundamental glass processing operations such as cleaving or splicing while conserving extreme wave-guiding properties of the active medium remain tricky points to address.
PCF amplifiers are then traditionally used in free space configurations, consequently losing the strength of the fiber technology, i.e its high potential of integration in fully monolithic systems.
We have developped a fully monolithic PCF amplifier module based on the largest core flexible single-moded amplifying fiber on the market, the DC-
200/40-PZ-Yb of NKT-photonics. The developed special combiner allows us to couple 6 pumps of 50 W and 5 W of signal at 1064 nm in the PCF fiber.
We produced 210 W of average power at 1064 nm in both single frequency and pulsed (100 ps/100 kW) regime, which is the highest power ever delivered by a monolithic PCF amplifier. The stainless steel output patchcord of the module is ended by high power SMA connector including mJ-class fused silica endcaps. PCF assembly is integrated in a thermally optimized, rugged module and was free runned for more than 25 days at > 100W average power with an excellent peak to peak power stability < 1%.
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Conference 9730:
Components and Packaging for Laser Systems II
9730-27, Session 7
(Invited Paper)
Jess V . Ford, Weatherford International Ltd . (United
States); Tom Haslett, Avo Photonics, Inc . (United States)
9730-29, Session 8
(Invited Paper)
Bojan Resan, Lumentum (Switzerland) and Univ . of
Applied Sciences and Arts Northwestern (Switzerland)
No Abstract Available
Black Gold, Texas Tea, fossil fuel, these are just a few euphemisms for the crude oil, a key commodity driving the economies of the world. As the quest for oil production continues worldwide, more and more emphasis is placed on the need to characterize the crude oil in situ before expensive production equipment is built at the well site. This requires the development of sensor technology that withstands the very harsh environments of the wellbore.
One area of active development is termed downhole fluid analysis, which is the implementation of optical spectroscopy and fluorimetry in the wellbore during exploration and development activities. This requires that the entire optical system, light sources, photodetectors, routing optics and control electronics, be transported to the measurement location either in a logging while drilling tool string or conveyed using wireline. This paper examines how a 20 channel photometric analyzer was packaged to address the thermal (up to 177°C), pressure (up to 20 kpsi) and vibration (up to 4.5 G) requirements dictated by the application. Specific emphasis will be placed on the optical component packaging and then the integration required for the entire assembly to meet the operational requirements. Data will be presented illustrating operation of the system at the elevated temperatures required.
9730-28, Session 7
Tobias Müller, Sebastian Haag, Daniel Zontar, Sebastian
Sauer, Christian Brecher, Fraunhofer-Institut für
Produktionstechnologie IPT (Germany); Christian Schlette,
Jürgen Rossmann, Institute for Man-Machine Interaction
(Germany)
9730-30, Session 8
Frank Fuchs, Gitterwerk GmbH (Germany)
Diffraction gratings are essential components of many modern pico- and femtosecond laser systems, with the most prominent application in the framework of chirped pulse amplification (CPA). Over the last years these laser systems have been introduced very successfully into many industrial applications, especially related to materials processing of various kind.
Driven by the demands of the market the employed laser sources are under constant development and optimization. In this context the optimization of the grating components is of pronounced interest due to their direct impact on the laser performance.
While the geometrical aspects of gratings are well understood and easily calculated, the diffraction performance has to be modeled carefully in close feedback to the manufacturing. Sadly this leaves the user out of the loop, and without good design rules for the compressor layout. Even worse textbook-knowledge about diffraction gratings mostly neglects the advances in grating design and manufacturing of the last decade(s).
In this contribution we provide a user oriented overview about the possibilities of modern grating design and manufacturing for high linedensity gratings. Both transmissive and reflective devices are discussed at the example of typical applications. We derive and provide design rules as a guidance for the grating user.
The assembly process of optical components consists of two phases – the alignment and the bonding phase. In the alignment phase, the limitation of the precision is given by the measurement equipment and the manipulation technology applied. Today’s micromanipulators in combination with beam imaging setups allow for an alignment in the range of far below 100nm.
However, precisely aligned optics need to be fixated in their position.
State of the art in optics bonding for laser systems is adhesive bonding with UV-curing adhesives. Adhesive bonding is a multi-factorial process and subject to statistical process deviations. Thus, process repeatability is decided and limited in the bonding phase. .As matters of fact, UV-curing adhesives inherit shrinkage effects during their curing process, making offsets for shrinkage compensation mandatory. Enhancing the process control of the adhesive bonding process is the major goal of the activities described in this paper. To improve the precision of shrinkage compensation a dynamic shrinkage prediction is envisioned by Fraunhofer IPT. Intense research activities are being practiced to gather a deeper understanding of the parameters influencing adhesive shrinkage behavior. These effects are of various nature – obviously being the raw adhesive material itself as well as its condition, the bonding geometry, environmental parameters like surrounding temperature and of course process parameters such as curing properties. Understanding the major parameters and linking them in a model-based shrinkage-prediction environment is the basis for improved process control. Results are being deployed by Fraunhofer in prototyping, as well as volume production solutions for laser systems.
9730-31, Session 8
Lawrence Shah, Nathan Bodnar, Joshua Bradford,
Benjamin Webb, Jess Lane, Michael Chini, Martin
Richardson, Univ . of Central Florida (United States)
Pulse duration and dispersion control are critical in high-energy chirped pulse amplification (CPA) systems. Practically, pulse compressor design is determined by the center wavelength and bandwidth of the system, the output beam size, and the chirped pulse duration. As such, the pulse stretcher must be designed to compensate the dispersion of the compressor as well as that of any optics in the amplifier path. This work will describe efforts to design and incorporate an integrated Bragg grating stretcher into a Ti:Sapphire system designed to produce 100 fs pulses with 5 TW peak power after compression. The compress is a conventional Treacy design consisting of two 1800 l/mm diffraction gratings providing -10 ps2 group delay dispersion (GDD) and +1 ps3 third order dispersion. In this application, the integrated Bragg grating must provide positive GDD and negative third order dispersion. Similar pulse stretching techniques have been used in relatively low energy fiber and solid-state systems, but to our knowledge this is first example of this technique in a TW class system. This work will also discuss the use of similar integrated Bragg gratings to stretch the pulse duration of pump lasers for optical parametric CPA (OPCPA). In each case, packaging the stretcher as an integrated device greatly reduces system footprint and alignment complexity and highlights further opportunities for integration in high-energy ultrashort pulse lasers.
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9730-32, Session 8
Conference 9730:
Components and Packaging for Laser Systems II
Vadim Smirnov, Eugeniu Rotari, Ruslan Vasilyeu, Oleg
Smolski, Alexei L . Glebov, Leonid Glebov, OptiGrate Corp .
(United States)
9730-35, Session 9
Martin Forrer, Hansruedi Moser, Hans Forrer, Dzelal Kura,
FISBA AG (Switzerland)
Stretchers and compressors based on volume chirped Bragg gratings
(CBGs) in photo thermo refractive (PTR) glass allowed design of compact
Ultra Short Pulse Laser (USPL) systems with high pulse energy and average power. The recent advances in CBG fabrication technologies enabled CBGs with spectral bandwidth exceeding 40 nm and diffraction efficiencies as high as 90%. The improvements in CBG bandwidth and efficiency broaden substantially their application range for USPL systems in the whole spectral region from 800 to 2500 nm. This paper will overview recent progress in the technology and applications of CBGs in PTR glass.
The engineering standard for slow axis collimation today is a spherical plano convex collimator lens. With increasing quality and assembly requirements, freeform optics are promoted for specific advantages. With the industrial requirement for scaling up to high quantities, the industrial production means have to be qualified for scalability and repeatability With the technology of precision glass molding a versatile production tool allows for high quality optical solutions. The results presented include optical design comparison of spherical to aspherical refractive and reflective slow axis collimation on a standard diode laser single emitter situation and the achievable component production quality.
9730-33, Session 8
Christophe Simon-Boisson, Olivier Chalus, Thales
Optronique S .A .S . (France); Daniel Sanchez, Michael
Hemmer, Matthias Baudisch, Seth Cousin, ICFO - Institut de Ciències Fotòniques (Spain); Jens Biegert, ICFO -
Institut de Ciències Fotòniques (Spain) and Institució
Catalana de Recerca i Estudis Avançats (Spain); Kevin
Zawilski, Peter G . Schunemann, BAE Systems (United
States); Vadim Smirnov, OptiGrate Corp . (United States);
Heinar Hoogland, Ronald Holzwarth, Menlo Systems GmbH
(Germany)
Here we report an OPCPA system generating high energy pulses centered at 7 ?m with a spectrum supporting a < 90 fs pulse duration, corresponding to sub-4 optical cycles. The OPCPA consists of three OPA stages which are pumped by an optically synchronized home built Ho:YLF picosecond CPA system operating at 2 ?m wavelength, both seeded by beams generated by the same multicolor fiber oscillator which deliver 3 outputs, one from the initial Er fiber oscillator and 2 outputs around 2 ?m after generation of a supercontinuum from the oscillator in a nonlinear fiber, 1 broadband to be mixed through DFG in a CSP crystal with output 1 to produce the MWIR seed of the OPCPA and 1 narrowband to seed the 2 ?m pump laser. This pump laser is a CPA using Chirped Volume Bragg Gratings for both stretcher and compressor. Active medium is Holmium doped YLF pumped by a 100
W cw 1.9 ?m Thulium fiber laser. A room temperature regenerative amplifier using a RTP Pockels cell delivers above 4 mJ whereas a cryogenically cooled amplifier has reached 40 mJ then compressed to 35 mJ with 11 ps pulse duration. To date, we have generated up to 550 ?J of energy around
7 ?m using only 12 mJ of our pump split into the 3 ZGP based OPCPA stages. The pump laser currently delivers up to 35 mJ at 100 Hz, implying straightforward scalability of the OPCPA to the mJ level in the near future
9730-36, Session 9
Fan Gao, Xiaojie Sun, Jing Hu, Xiang Zhang, Xiao Yuan,
Soochow Univ . (China)
The uniform near-field distribution and focusing characteristics of laser beams, which is closely connected with spatial frequencies and wavefront distortion of beams, are very important for high energy and power laser applications, such as laser processing and laser fusion, etc. The deformable mirror and spatial filter are used to compensate for the wavefront distortion and filter out the high frequencies, respectively. However, the medium and high distortions in laser beams are difficult to correct with the deformable mirror and spatial filter. The transmitting volume Bragg gratings (TBGs) has been used for angular filtering to clean the amplitude modulations of laser beams, and may be used to compensate for wavefront distortion.
In this paper, the wavefront characteristics of filtered beams through the TBG are discussed. The wavefront distortion corrected with TBG is demonstrated with a 1053 nm laser beam. The TBG used in the experiment has the angular selectivity of 1.3 mrad and period of 2?m. The wavefront distortion distribution of the source beam is modulated with a hard-edge aperture. The results show that the PV value and RMS value of the filtered beam are reduced from 0.293 ? to 0.169 ? and 0.054 ? to 0.032 ?, and the
Strehl ratio of filtered beam is increased from 0.91 to 0.98. The focusing property of the output beam is improved, and the encircled energy of the beam is improved from 95% in 31.2 ?rad to 95% in 29.4 ?rad, which may be a simple and effective approach for high energy and power laser applications.
9730-37, Session 9
Matthew O . Currie, Paul Blair, Roy McBride, Eoin Murphy,
PowerPhotonic Ltd . (United Kingdom)
9730-34, Session 9
(Invited Paper)
Eric C . Honea, Robert Afzal, Matthias Savage-Leuchs,
Dan Hu, Craig Robin, Lockheed Martin Laser and Sensor
Systems (United States)
We describe the design and fabrication of smooth and continuous customized refractive diffusers for the beamshaping of high power lasers, specifically lasers in which a low diffusion angle is required. Traditional diffusers often have randomised surfaces with strong high frequency peaks in their spatial frequency content. However, these diffusers are not suitable for use in high power laser systems where diffraction angles can approach required diffusion angles. Diffraction angles which exceed diffusion angles present as overall system loss, which in high power laser systems may be unacceptable as they may cause component damage or catastrophic failure.
to be uploaded later.
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We show that precise definition of the spatial frequency content of a surface over a lower frequency range allows for the maximisation of diffuser efficiency and performance, even at diffusion angles of only a few milliradians or less. Additionally, the image plane intensity distribution can be extensively shaped in order to obtain favourable processing conditions for numerous systems. By introducing a novel implementation of an Iterative
Fourier Transform (IFT) algorithm, we present a method to design and subsequently fabricate highly customised beamshaping diffusers that retain maximum efficiency even when used at low diffusion angles.
9730-38, Session 9
Conference 9730:
Components and Packaging for Laser Systems II
Christian Wenzel, Innolite GmbH (Germany) monolithic fiber spools; detachable and repeatable fiber collimators; low loss fiber-to-fiber coupling schemes; and high power fiber-coupled isolators.
9730-40, Session 10
Claude Aguergaray, Catherine Lesaux, Léo Lebrun, Marc
Faucon, Rainer Kling, Christophe Pierre, Johan Boullet,
ALPhANOV (France)
Camera objectives or laser focusing units consist of complex lens systems with multiple lenses. The optical performance of such complex lens systems is depended on the correct positioning of lenses in the system. Deviations in location or angle within the system directly affect the achievable image quality. To optimize the achievable performance of lens systems, these errors can be corrected by machining the mount of the lens with respect to the optical axis.
The Innolite GmbH and Opto Alignment Technology have developed a novel machine for such center turning operation. A confocal laser reflection measurement system determines the absolute position of the optical axis with reference to the spindle axis. As a strong advantage compared to autocollimator measurements the utilized Opto-Alignment Technology is capable of performing centration and tilt measurements without changing objectives on any radius surface from 2 mm to infinity and lens diameters from 1 mm to 300 mm, including cylinder, aspheric, and parabolic surfaces.
In addition, it performs significantly better on coated lenses.
The optical axis is skewed and offset in reference to the spindle axis as determined by the measurement. Using the information about the mount and all reference surfaces, a machine program for an untrue turning process is calculated from this data in a fully automated manner. Since the optical axis is not collinear with the spindle axis, the diamond tool compensates for these linear and tilt deviations with small correction movements. This results in a simple machine setup where the control system works as an electronic alignment chuck. Remaining eccentricity of <1 µ m and angular errors of < 5 sec are typical alignment results.
High average power fiber-laser require today the development of a technology capable of transporting and managing such intense beams.
Despite a conjoint improvement of their architectures, coupling light from one fiber to the next remain particularly challenging at high average power due to light leaking into the cladding that eventually destroys the fiber.
Several techniques have demonstrated good performances to capture and dissipate this undesirable light. All of them aim at depositing a guiding material on the surface of the fiber that forces the light out. Amongst them, the deposition of silica particles and surface etching with hydrofluoricacid have shown the best performances. But both their implementation is difficult due to a complicated process to deposit the silica micro-particles or to the toxic chemicals needed.
We propose here a simple technique based on laser surface texturization to create efficient, high-power, light-strippers. Using a UV laser, we directly micro-machine the surface of the fiber. We have stripped 98% of the light coupled in the cladding, up to several tens of Watts, and reduced the NA from 0.3 to 0.06. Thus demonstrating the superior ability of our technique to evacuate light with smaller NA. The process described herein can be used on any type of fiber, it is more efficient, very simple, hazard-free and perfectly repeatable.
We will present the various depths and geometries we have tested together with our high power (>200W) tests. We will also present light-strippers machined with a 1030nm laser, alongside structural and mechanical analyses of the samples.
9730-39, Session 10
(Invited
Paper)
Daniel Creeden, Benjamin R . Johnson, Casey W . Jones,
Charles R . Ibach, Michael L . Lemons, Peter A . Budni, James
P . Zona, Adam J . Marcinuk, Chris L . Willis, James Sweeney,
Scott D . Setzler, BAE Systems (United States)
High power continuous and pulsed fiber lasers and amplifiers have become more prevalent in laser systems over the last ten years. In fielding such systems, strong environmental and operational factors drive the packaging of the components. These include large operational temperature ranges, non-standard wavelengths of operation, strong vibration, and lack of water cooling. Typical commercial fiber components are not designed to survive these types of environments. Based on these constraints, we have had to develop and test a wide range of customized fiber-based components and systems to survive in these conditions. In this paper, we discuss some of those designs and detail the testing performed on those systems and components. This includes the use of commercial off-the-shelf (COTS) components, modified to survive extended temperature ranges, as well as customized components designed specifically for performance in harsh environments. Some of these custom components include: ruggedized/
9730-41, Session 10
Mathias Mende, Jürgen Kohlhaas, Wolfgang Ebert,
LASEROPTIK GmbH (Germany)
Laser material processing plays an important role in the fabrication of the crucial parts for state-of-the-art smartphones and tablets. With industrial line beam systems a line shaped beam with a length above one meter and an average power of several thousand watts can be realized. To ensure excellent long axis beam homogeneity, demanding specifications regarding the substrate surface form tolerances and the coating uniformity have to be achieved for each line beam optic. In addition, a high laser damage threshold and a low defect density are required for the coatings. In order to meet these requirements, the MAXIMA ion beam sputtering machine was developed and built by LASEROPTIK.
This contribution describes the functional principle of MAXIMA deposition machine, which adapts the IBS technology with its highest coating quality to the field of large area deposition. Furthermore, recent developments regarding the process control by optical broadband monitoring are discussed. Finally experimental results on different thin film characteristics as for example the coating uniformity for plane and curved surfaces, the microstructure of multilayers and the laser damage resistance are presented.
84 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9730:
Components and Packaging for Laser Systems II
9730-42, Session 10
Lynda E . Busse, Jesse A . Frantz, U .S . Naval Research Lab .
(United States); Menelaos K . Poutous, Rajendra Joshi,
The Univ . of North Carolina at Charlotte (United States);
Ishwar D . Aggarwal, Sotera Defense Solutions, Inc . (United
States); Jasbinder S . Sanghera, U .S . Naval Research Lab .
(United States)
High transmission as well as environmental durability of silica glass exit apertures are critical for their practical use in kW-level, high power laser systems. In actual land, sea and marine environments, these windows can, for example, be vulnerable to rain and sand erosion as well as salt/ fog conditions. These exit aperture windows have traditionally had antireflective (AR) coatings applied to reduce surface reflections, but these coatings can suffer delamination and damage under adverse environmental conditions. An alternative approach is to directly etch anti-reflective surface structures (ARSS) on the windows, with no extraneous materials on the surface. We have demonstrated high transmission (> 99.9%T) and very high laser damage thresholds (100 J/cm2) at 1.06 µ m for silica windows with ARSS. In this paper we will present results for MILSPEC durability tests on silica windows both with and without ARSS that were conducted at a government facility, involving rain and sand erosion as well as salt fog testing. Results will be reported using a variety of test conditions, such as variable impact speeds and angles of incidence. In light of these results, we will discuss their utility as exit apertures in high energy laser systems.
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9731-1, Session 1
µ
(Invited Paper)
Kevin F . Lee, Christian Mohr, Jie Jiang, IMRA America,
Inc . (United States); Peter G . Schunemann, BAE Systems
(United States); Konstantin L . Vodopyanov, CREOL, The
College of Optics and Photonics, Univ . of Central Florida
(United States); Martin E Fermann, IMRA America, Inc .
(United States)
Degenerate optical parametric oscillators (OPOs) divide optical frequencies by two with only modest pumping. This makes them promising mid-infrared frequency comb sources. Our measurements show that our degenerate
OPO preserves the frequency comb stability of the pump to sub-Hz levels.
However, degenerate OPOs are often overlooked due to their interferometric cavity stabilization requirements. We find that the stability requirements of our system are actually much simpler, because thermal feedback results in self-stabilization. When the OPO is oscillating, absorption of the intracavity field increases the crystal temperature, and subsequently the effective cavity length, which is fortunately the right direction to stabilize degenerate oscillation in our system. Our OPO is based on an orientation-patterned
GaAs crystal, pumped by a stabilized 2 W, 418 MHz, optically-referenced
Tm frequency comb, generating a broadband, mid-infrared frequency comb centered at 4 µ m. We have observed continuous OPO oscillation for almost an hour without cavity length feedback. These measurements show that a degenerate OPO can serve as a simple device to downconvert a frequency comb.
applications including trace molecular detection and chemical sensing with massively parallel spectral data acquisition.
9731-3, Session 2
(Invited Paper)
Wei Liang, Anatoliy A . Savchenkov, OEwaves, Inc . (United
States); James F . McMillan, Columbia Univ . (United States);
Zhenda Xie, Univ . of California, Los Angeles (United
States); Jan Burkhart, Columbia Univ . (United States);
Vladimir S . Ilchenko, OEwaves, Inc . (United States); Chee
Wei Wong, Univ . of California, Los Angeles (United States);
Andrey B . Matsko, Lute Maleki, OEwaves, Inc . (United
States)
We have demonstrated generation of multi-octave CW optical spectrum in a micro-resonator optical parametric oscillator (OPO) pumped with milliwatt level CW light. The generated harmonics span from UV to near-IR.
The generation is facilitated by linear interaction among different mode families in the resonator that phase matches the nonlinear frequency conversion. By selecting proper experimental conditions the system can efficiently generate different combinations of spectral harmonics separated by hundreds of THz. Because of the significant frequency difference between the OPO harmonics, it is possible to separate them efficiently using a diffraction grating. The system can be heterogeneously integrated as a chip scale device of very low volume and power consumption. It can be potentially used to generate quantum correlated photon pairs, or used as an ultra narrow linewidth source to seed high power laser at various visible wavelengths.
9731-2, Session 1
µ
Viktor O . Smolski, Jia Xu, CREOL, The College of Optics and Photonics, Univ . of Central Florida (United States);
Peter G . Schunemann, BAE Systems (United States);
Konstantin L . Vodopyanov, CREOL, The College of Optics and Photonics, Univ . of Central Florida (United States)
We study coherence properties of a more-than-octave-wide (2.5-7.5
µ m) mid-IR frequency comb based on a 2µ m Tm-fiber-laser-pumped degenerate (subharmonic) optical parametric oscillator (OPO) that uses orientation-patterned gallium arsenide (OP-GaAs) as gain element. By varying intracavity dispersion, we observed a ‘phase’ transition from a single-comb state (at exactly OPO degeneracy) to a two-comb state (neardegenerate operation), characterized by two spectrally overlapping combs
(signal and idler) with distinct carrier-envelope offset frequencies. We achieve this by generating a supercontinuum (SC) from the mode-locked Tm laser that spans most of the near-IR range, and observing RF beats between the SC and parasitic sum-frequency light (pump + OPO) that also falls into the near-IR. We found RF linewidth to be <15 Hz (a resolution of our spectrum analyzer), which proves that coherence of the pump laser comb is preserved to a high degree in a subharmonic OPO. Transition to a two-comb state was characterized by a symmetric splitting of the RF peak. Low pump threshold (down to 7 mW), high (73 mW) average power and high (up to
90%) pump depletion make this comb source very attractive for numerous
9731-4, Session 2
(Invited Paper)
Stojan Radic, Univ . of California, San Diego (United States)
In contrast to conventional methods for frequency generation that rely on intense, pulsed source seeding of nonlinear process, new class of parametric techniques now allow for low-power generation over wide spectral ranges.
To generate new optical frequency, it is necessary to induce efficient three- or four-photon process in selected physical platform. The efficiency of such process is defined by a product of interacting intensity, material nonlinearity and interaction length. A construction of long, lossless and dispersionless nonlinear waveguide can, at least in principle, alleviate the need to seed the frequency generation using a peak-intense source such as mode-locked laser. Indeed, if parametric mixer can be efficiently seeded by stabilized continuous-wave laser, then it can be expected that newly generated frequencies would be accompanied by qualitatively lower noise level.
Recognizing this challenge, we describe the principle, construction and performance of CW-seeded frequency combs. We show that new device can generate power-equalized combs over hundreds of nanometers, while being seeded by telecom-grade (Watt-scale), rather than kWatt-scale pulsed sources. The ability to replicate CW source emission in travelingwave parametric mixer is identified as a basic advantage over conventional, resonance-based frequency generators. More importantly, this technique feature was recently leveraged towards the construction of low-noise, frequency-tunable combs that cannot be generated, even in principle,
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bay any comparable technique. The implications new technology will be illustrated with sensing and communication applications.
9731-5, Session 3
Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV
(Keynote Presentation)
Alexey Avdokhin, Valentin P . Gapontsev, IPG Photonics
Corp . (United States) components: an Yb-fiber oscillator, a pulse stretcher, amplifiers and a pulse compressor. The output power of 2 mW from the oscillator was amplified up to 23 W through two Yb-doped fiber based pre-amplifiers and an Ybdoped photonic crystal fiber based power amplifier. The pulse duration after compression was as short as 200 fs, and an intracavity pulse energy as high as 100 ?J was achieved. The resulting odd-order harmonics radiations extended down to 30 nm, and the 7th harmonic radiation centered at
149 nm had an average output power of up to 0.5 mW. The 7th harmonic radiation had a brilliance of 1.9?10^16(photons/s/mm^2/mrad^2/0.1%BW), which is comparable to a synchrotron radiation at the same wavelength. A computer controlled phase-lock system was able to maintain the intracavity phase-locking for more than 24 hours.
Remarkably successful commercial deployment of high power fiber laser technology has revolutionized many areas of laser applications by providing significantly more economical, efficient and compact solutions than the ones offered by alternative laser platforms. However, since most of the commercial fiber lasers operate in the infrared part of the spectrum, applications that required high power visible or UV radiation, for a long time still had to continue relying on gas lasers or solid state lasers with frequency conversion. Even though the process of frequency conversion of light generated by fiber lasers has been successfully employed for many years, due to physical limitations of the active fiber medium generation of high average power radiation in visible and UV spectral ranges has been a very challenging task. Only over the last years, with IPG launch of a program on development of commercial high-power fiber-based visible and UV laser sources, it became feasible to overcome many of the existing limitations and demonstrate possibility of generating light with high and ultrahigh average power levels in visible and UV spectral ranges. Inherent versatility of fiber lasers’ design has allowed adapting key laser parameters to a broad range of requirements, while maintaining all the other benefits of fiber approach
– very high efficiency, compactness and low cost. In this presentation, we will report on our progress in satisfying these real-world requirements and discuss various solutions which are developed or under development for different existing and emerging applications. The high-power fiber laser platforms which we will overview include highly-stable high-power single-frequency green lasers for demanding scientific markets, as well as high-lumen broadband laser sources of inherently de-speckled green and red light for cinema projection and entertainment applications. We will also discuss high average power QCW green and UV lasers for cutting, welding and annealing, as well as high peak power pulsed green and UV lasers for micromachining and laser surface cleaning; single-mode lasers for highprecision applications, as well as ultrahigh power multimode lasers for material processing; lasers with other colors, i.e. orange, for medical and other emerging applications; and a lot more.
9731-7, Session 3
Xiaodong Mu, Paul Steinvurzel, Todd S . Rose, William
T . Lotshaw, Steven M . Beck, James H . Clemmons, The
Aerospace Corp . (United States)
Frequency up-conversion of fiber lasers is an attractive method for generating compact and efficient deep ultraviolet (DUV) radiation, which has a variety of applications in Lidar, spectroscopy, lithography, and material processing. Here, we demonstrate high efficiency DUV conversion to 266 nm through frequency quadrupling of a 1064-nm Yb-doped fiber master oscillator power amplifier (MOPA). The MOPA consists of a 1064-nm diode seeder (master oscillator) and a 3-stage fiber amplifier containing conventional double-clad polarization-maintaining Yb-doped fibers. The average output power, spectral bandwidth, pulse width and repetition rate are 1.31 W, 40 pm (10.6 GHz), 1.42 ns and 20 kHz, respectively. The secondharmonic is generated in two 15-mm long critically phase-matched LBO crystals with walk-off compensating alignment. We achieve an output power of 0.92 W at 532 nm and a second harmonic generation (SHG) efficiency of
74%. By comparison, the maximum SHG efficiency in a single LBO crystal is measured to be only ~59%. The fourth-harmonic generation (FHG) is achieved in a 10-mm long BBO crystal. For an input power of 0.86 W, we generated 0.40 W at 266 nm, corresponding to a conversion efficiency of
47%. The overall FHG efficiency from 1064 nm to 266 nm is 30%. To the best of our knowledge, this is the highest conversion efficiency reported in a single-pass FHG. We found that the pumping ratio of the 3 stages of the fiber amplifier is essential for reaching such a high FHG efficiency.
9731-6, Session 3
(Invited
Paper)
Shuntaro Tani, Akira Ozawa, Zhigang Zhao, Makoto
Kuwata-Gonokami, Yohei Kobayashi, The Univ . of Tokyo
(Japan)
High harmonic generation (HHG) in an enhancement cavity provides high-repetition-rate coherent light sources in the vacuum ultraviolet (vuv) to soft x-ray region, with key applications in photoemission spectroscopy and diffractometry. One major drawback of HHG with high repetition rates, typically 100 MHz, was the relatively low conversion efficiency from the fundamental pulses to the higher order harmonics ones due to the smaller pulse energies. To achieve sufficiently high output power, we developed a
30-m long enhancement cavity system driven by a 10-MHz Yb-doped fiber laser system. The lowered repetition rate increased the pulse energies and realized the high-conversion efficiency of 10^?6 while keeping an adequate repetition rate for spectroscopic applications.
The seed laser for the external cavity consisted of the following
9731-8, Session 3
Julian Hofmann, Nils Werner, David Feise, Alexander
Sahm, Roland Bege, Bernd Eppich, Gunnar Blume, Katrin
Paschke, Ferdinand-Braun-Institut (Germany)
Compact and efficient laser sources around 560 nm are demanded for several medical applications as well as confocal microscopy and atom spectroscopy. Until today, this wavelength region cannot be reached by direct emitting semiconductor-based laser sources with sufficient efficiency.
Therefore, the most promising approach for compact and efficient laser sources are lasers emitting around 1120 nm combined with second harmonic generation.
As the different applications for laser light at 560 nm have very different requirements on e.g. the power, the spectral linewidth and the beam quality of the emitted light, we have developed three micro integrated laser
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modules to fulfill the demands of each application. The modules for the low power applications (power < 100 mW) consist only of a laser with an internal distributed Bragg reflector [1], a grinlens and a ridge-waveguide crystal for second harmonic generation. This most simple setup is easy to align and low cost but limited in power and linewidth. For high power applications (power > 200 mW) we boost the power of the laser with a tapered amplifier in a master-oscillator power-amplifier configuration [2] and use either bulk or planar-waveguide crystals for second harmonic generation. This - especially for the planar-waveguide crystal - much more complex setup offers higher power and better linewidth as we use an optical isolator to shield the laser from back-reflections here.
At the conference we will present a theoretical analysis of the expected performance of the different setups and compare the results with the results of our experimental analysis.
[1] Paschke, K.; Wenzel, H.; Fiebig, C.; Blume, G.; Bugge, F.; Fricke, J. and
Erbert, G., “High Brightness, Narrow Bandwidth DBR Diode Lasers at 1120 nm”, IEEE Photonics Technology Letters., vol. 25, , pp. 1951-1954 (2013)
[2] Spießberger, S.; Schiemangk, M.; Sahm, A.; Wicht, A.; Wenzel, H.; Peters,
A.; Erbert, G. and Tränkle, G., “Micro-integrated 1 Watt semiconductor laser system with a linewidth of 3.6kHz”,Optics Express, vol. 19, , pp. 7077-7083
(2011)
9731-9, Session 3
Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV
Norman Ruhnke, André Müller, Bernd Eppich, Reiner
Güther, Martin Maiwald, Bernd Sumpf, Götz Erbert,
Günther Tränkle, Ferdinand-Braun-Institut (Germany)
Photonics - Mid-Infrared Lasers (United States); Viktor
Smolski, IPG Photonics Mid Infrared Lasers (United States);
Sergey B . Mirov, IPG Photonics - Mid-Infrared Lasers
(United States) and The Univ . of Alabama at Birmingham
(United States); Valentin P . Gapontsev, IPG Photonics
Corp . (United States)
Cr2+ doped polycrystalline ZnS and ZnSe possess a unique blend of physical, spectroscopic, and technological parameters. Four-level energy structure, broad vibronic emission bands, absence of excited-state absorption, and close to 100% quantum efficiency of fluorescence enable room-temperature mid-IR lasers with power in excess of 50 W and a broad tuning range (1.9 – 3.3 µ m). Kerr-lens mode-locked polycrystalline
Cr2+:ZnS lasers with up to 2 W average power and <29 fs pulse duration at 2.4 µ m central wavelength were recently demonstrated. Polycrystalline
Cr2+:ZnS/ZnSe consist of a multitude of microscopic single-crystal grains.
The broad distribution of grain sizes and orientations results in so-called random quasi-phase-matching (RQPM). The distinctive features of RQPM are a linear dependence of the conversion yield with length of the medium and ultra-wide bandwidth. Combination of RQPM in polycrystals with high nonlinearity of II-VI semiconductors opens several avenues for efficient frequency conversion of few-cycle pulses directly in the gain medium of the mode-locked laser. We demonstrate that significant fraction of mid-IR laser emission can be converted to spectrally broad (up to 22 THz, FWHM) second harmonic pulses (SHG). The SHG power (up to 250 mW) is high enough for real-world applications. We also observe generation of higher optical harmonics as well as sum frequency mixing between mid-IR pulses and a cw pump beam. Furthermore, the MW-level optical power inside the resonator of mode-locked laser allows us to consider efficient downconversion in polycrystalline Cr2+:ZnS/ZnSe, which may lead to ultrafast oscillators with exceptionally broad spectral coverage spanning from 2 to 6
µ m.
Deep ultraviolet (DUV) lasers emitting below 300 nm are of great interest for many applications, for instance in medical diagnostics or for detecting biological agents. Established DUV lasers, e.g. gas lasers or frequency quadrupled solid-state lasers, are relatively bulky and have high power consumptions. A compact and reliable laser diode based system emitting in the DUV could help to address applications in environments where a portable and robust light source with low power consumption is needed.
In this work, a compact DUV laser system based on single-pass frequency doubling of high-power GaN diode laser emission is presented. A commercially available high-power GaN laser diode from OSRAM Opto
Semiconductors serves as a pump source. The laser diode is spectrally stabilized in an external cavity diode laser (ECDL) setup in Littrow configuration. The ECDL system reaches a maximum optical output power of 700 mW, maintaining narrowband emission below 60 pm (FWHM) at 445 nm over the entire operating range.
By direct single-pass frequency doubling in a BBO crystal with a length of
7.5 mm a maximum DUV output power of 16 ?W at a wavelength of 222.5 nm is generated.
The presented concept enables compact and efficient diode laser based light sources emitting in the DUV spectral range that are potentially suitable for field applications where small footprint and low power consumption is essential.
9731-10, Session 4
(Invited
Paper)
Sergey Vasilyev, Igor S . Moskalev, Mikhail S . Mirov, IPG
9731-11, Session 4
Julian Klein, Walter Schottky Institut (Germany) and
Technische Univ . München (Germany); Jakob Wierzbowski,
Armin Regler, Jonathan Becker, Walter Schottky Institut
(Germany); Florian Heimbach, Technische Univ . München
(Germany); Michael Kaniber, Walter Schottky Institut
(Germany); Kai Müller, Stanford Univ . (United States) and
Walter Schottky Institut (Germany); Jonathan J . Finley,
Walter Schottky Institut (Germany)
The emergence of truly two-dimensional materials like graphene augmented the range of commercially available material systems for future utilization in sophisticated electronic and optoelectronic device architecture. Especially, the semiconducting transition metal dichalcogenides (SMTDs) MoS2, MoSe2,
WS2 and WSe2 play a key role in bridging the gap among bandgap-less graphene and insulating hBN. The outstanding properties of STMDs are based on a direct bandgap in the monolayer limit with an optical transition in the visible. The intrinsic electronic and optical signature in few-layer crystals is strongly driven by crystallographic symmetry properties. The inherently broken inversion symmetry in monolayer crystals manifests their recently reported advantage for valleytronic applications.
Here, we present intense tunability of second-harmonic generation in naturally inversion symmetric 2H stacked bilayer MoS2. Control of the nonlinear conversion efficiency is achieved by altering the crystal’s inversion symmetry via immense externally applied perpendicular electric fields. This is established in a novel lithographically designed Si(n)-SiO2-STMD-Al2O3metal micro-capacitor device with optical access. We excite bilayer MoS2 crystals with ultrashort pulses of ~ 70 fs within a spectral window of 840
– 1000 nm (1.24 – 1.47 eV). We observe a significant tunability throughout
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Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV the probed region with a ~ 60 fold conversion amplification at its optimum.
We attribute the spectral sensitivity of the electrically controlled secondharmonic generation to the material intrinsic second-harmonic response.
Our results demonstrate the potential of efficient electrically driven broadband frequency doubling by external control of the symmetry properties of 2H bilayer MoS2.
9731-14, Session 5
Vladimr L . Tassev, Rita D . Peterson, Shivashankar Vangala,
Michael Snure, Martin Kimani, Air Force Research Lab .
(United States)
9731-12, Session 4
Peter G . Schunemann, Daniel J . Magarrell, Lee Mohnkern,
Leonard A . Pomeranz, BAE Systems (United States)
Quasi-phase-matched semiconductors represent the future of mid-IR nonlinear optical materials, and orientation-patterned GaAs (OP-GaAs) is the first successful incarnation of this technology. GaAs offers very high nonlinearity (d14=94 pm/V) and thermal conductivity (55W/mK), and when grown from the vapor phase exhibits extremely low 2-?m absorption losses (< 0.01 cm-1). The application of OP-GaAs has been limited by the availability of samples with sufficient thickness, grating quality, and transparency for practical device applications. The primary obstacle to aperture scaling OP-GaAs has been the tapering of domain wall boundaries: instead of parallel vertical propagation of both polarities, it is observed that domains nucleating on the original (etched) substrate orientation grow gradually wider at the expense of the adjacent domains growing on the inverted layer. As a result the duty cycle of the MBE template gradually shifts away from the optimal 50:50 (degrading conversion efficiency) during
HVPE growth until ultimately the inverted domains are annihilated. Previous work has shown that the domain spreading angle can be minimized by growth at lower temperatures (680°C), but we have achieved better material quality and OPO performance for growth closer to 710°C at the expense of worse domain spreading. In parallel work on orientationpatterned gallium phosphide (OP-GaP) we observed near-perfect domain propagation at elevated growth temperatures (795°C) and V/III ratios > 6.
In this work we examined the effect of V/III ratio, growth rate, and growth temperature on domain propagation in OP-GaAs and OP-GaP. Maximum thickness and resulting OPO/DFG performance will be reported.
Frequency conversion in orientation-patterned (OP) materials is a leading approach for generating tunable mid- and long-wave coherent infrared radiation for a wide variety of applications. The strong interest led to intensive investigation of a number of nonlinear optical materials. GaP is an especially promising material, due to its unique properties—high nonlinear susceptibility, low two-photon absorption in the convenient pumping range
1–1.7 µ m and high thermal conductivity. Growth of OPGaP has encountered several challenges, such as relatively low quality of commercially available
GaP wafers, and uncontrollable parasitic nucleation that reduces the growth rate and the layer quality, especially during longer runs. Here we describe an original approach for producing thick, high-quality OPGaP with excellent domain fidelity via a one-step HVPE homo or heteroepitaxial growth process with growth rate of about 100 µ m/h. Two-inch wafer bonded OPGaP templates and templates in which polarity alternation was achieved in a MBE assisted procedure were used. AFM, SEM, XRD, EDS and TEM showed smooth surface morphology and high crystalline quality, while optical characterization confirmed substantial reduction of the 2-4
µ m absorption typical for all n-type GaP samples, low 2PA (??
≤ 0.1 cm/GW, compare with 15-16 cm/GW for GaAs) and low optical losses. Important crystallographic considerations on how to avoid the appearance of (111)p facet that could overgrow the pattern, and why alternating the polarity may favor the growth near the interface are also provided.
9731-15, Session 5
Shekhar Guha, Air Force Research Lab . (United States);
Jean Wei, Joel M . Murray, Jacob O . Barnes, Air Force
Research Lab . (United States) and UES, Inc . (United
States); Peter G . Schunemann, BAE Systems (United
States)
9731-13, Session 4
Christopher G . Brown, Univ . Research Foundation
(United States); Steven R . Bowman, Jennifer K . Hite,
Jaime A . Freitas, Francis J . Kub, Charles R . Eddy Jr ., Igor
Vurgaftman, Jerry R . Meyer, U .S . Naval Research Lab .
(United States); Jacob H . Leach, Kevin Udwary, Kyma
Technologies, Inc . (United States)
Gallium Nitride’s (GaN) material properties of broadband transparency, high thermal conductivity, and wide-band gap make it a promising candidate for high power frequency conversion devices. GaN possesses a nonlinear susceptibility similar in magnitude to lithium niobate, due to strong internal polarization, but conventional phase matching is prevented due to GaN’s weak birefringence. In order to obtain efficient nonlinear optic frequency conversion, patterned inversion growth has been developed to induce quasi-phase matching (QPM). We have fabricated and tested periodically oriented gallium nitride (PO-GaN) devices in order to obtain QPM frequency conversion. We report recent measurements of second harmonic generation, free carrier absorption, bulk scattering losses, and absorption due to unintentionally doped impurities.
Frequency doubling, tripling and quadrupling of carbon dioxide lasers operating in the 9.2 to 10.8 ?m wavelength range provide the means to generate tunable radiation in the 4.6 to 5.4 ?m, 3.1 to 3.6 ?m and 2.3 to 2.7
?m wavelength ranges, respectively. Orientation patterned GaAs and GaP are promising nonlinear optical materials for these processes because of their high nonlinearity and low absorption at the relevant wavelengths. In order to calculate the expected conversion efficiencies, one must have an accurate knowledge of the material d coefficient for these interactions at each wavelength. Along with the dispersion of the refractive indices, it is also important to know the wavelength and temperature dependence of the absorption coefficient of the materials.
In the infrared spectral range, neither the wavelength dependence of the d coefficient value nor the temperature and wavelength dependence of the absorption coefficients of GaAs and GaP are readily available. We have therefore undertaken a detailed study to determine these values.
The absorption coefficients of crystals grown by the hydride vapor phase epitaxy (HVPE) process have been measured over a temperature range of 77 K to 295 K for the 1 to 20 µ m wavelength range and compared with materials grown from melt and slow cooling. Using a picosecond laser tunable in the 2 to 10 µ m wavelength range, the values of the d coefficient were measured using HVPE-grown single crystals.
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9731-16, Session 5
Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV
Mousa Ayoub, Hannes Futterlieb, Jörg Imbrock, Cornelia
Denz, Westfälische Wilhelms-Univ . Münster (Germany)
9731-46, Session 5
(Keynote Presentation)
Eric W . Van Stryland, Peng Zhao, Trenton Ensley, Matthew
C . Reichert, David J . Hagan, CREOL, The College of Optics and Photonics, Univ . of Central Florida (United States)
Ferroelectrics are pivotal materials in devices for sensor applications, data storage, and selective optical parametric processes. Methods for the accurate characterization of these materials regarding the dynamics of their growth and switching are critical in the exploration and understanding of the outstanding properties for technological developments. This complex dynamics has been well studied by past work. However, how the phase transition of relaxor ferroelectrics in fact takes place is still under active debate. The combination of the measurements of the characteristics, achieved until now with, the visualization in the volume is still an open requirement. In this contribution we demonstrate the first three-dimensional monitoring of the evolution of the spontaneous polarization (Ps) during transition from the para- to ferroelectric phase and vice versa. This allows us to determine the Curie temperature range more accurately, what is required for relaxor ferroelectrics. The monitoring is based on a key sensitive feature to the domain wall. This is optically provided by Cherenkov-type secondharmonic microscopy. Here we identify chronologically the dimension of the evolution process. The microscopic measurements are combined with second-harmonic measurements in far field. The medium studied here, is a relaxor random strontium barium niobate (SBN), in which Ps is represented by 3D needle-like objects (several hundreds of micrometers in length).
The quantitative value of Ps is recorded simultaneously by measuring the poling current. Our results pave the way for deeper understanding of the ferroelectric nature for more accurate modeling of this complex behavior that is fundamental for all applications of ferroelectrics.
9731-17, Session 5
Lars G . Holmen, Magnus W . Haakestad, Norwegian
Defence Research Establishment (Norway)
We use our recently developed femtosecond excitation-probe beamdeflection (BD) method to measure the temporal dynamics of nonlinear refraction in various liquids and gases for different polarization combinations. This allows us to determine the temporal response function of these materials. In turn, this allows us to predict the outcome of other experiments, e.g. Z-scan, as a function of the pulsewidth used. For gases, the coherent revivals reveal the IR rotational spectrum including changes in line-width with rotational quantum number. Comparisons can also be made between the second hyperpolarizability in liquid and gas phase.
9731-18, Session 6
Stefan Kedenburg, Tobias R . J . Steinle, Florian Mörz, Andy
Steinmann, Harald Giessen, Univ . Stuttgart (Germany)
We demonstrate a tunable and robust femtosecond supercontinuum source with a maximum output power of 550 mW and a maximum spectral width of up to 2.0 ?m which can cover the mid-infrared region from 2.3
?m up to 4.9 ?m by tuning the pump wavelength. As light source we use a synchronously pumped fiber-feedback OPO and a subsequent OPA which delivers femtosecond, Watt level idler pulses tunable between 2.5 ?m and
4.1 ?m. These pulses are launched into As2S3 chalcogenide step-index fibers with core diameters of 7 and 9 ?m. The spectral behavior of the supercontinuum is investigated by changing the pump wavelength, core diameter, fiber length, and pump power. Self-phase modulation is identified as the main broadening mechanism in the normal dispersion regime. This source promises to be an excellent laboratory tool for infrared spectroscopy owing to its high brilliance as demonstrated for the CS2-absorption bands around 3.5 ?m.
Several types of infrared sensors are based on sensitive focal plane arrays.
In such sensors, the intensity will typically increase by a factor 10^7 at the focal plane, compared to the intensity of the incoming radiation. Such arrays are thus vulnerable when illuminated with high-intensity laser pulses. One solution for protecting the array against such pulses is to use an optical limiter, which is a passive device that blocks radiation with high intensity and transmits radiation with low intensity.
We here present results where carbon disulfide (CS2) has been tested as an optical limiting material when illuminated with 25 ns pulses with up to several hundred mJ energy at 2.05 µ m wavelength. The laser had a beam quality M^2=1.5, and the beam was focused onto a CS2-cell using a lens with an effective f-number of 10 and a focal length of 50 mm. The light emerging from the CS2 cell was refocused onto an aperture, with a field of view of 1.4 mrad. Pulse energies of up to 150 mJ were incident on the cell, while at most
0.6 mJ was transmitted through the aperture, due to dielectric breakdown and beam filamentation in the CS2 cell at high pulse energies. In addition, the nonlinear index of refraction of CS2 at 2.05 µ m wavelength was measured using the z-scan technique, yielding a value of (2.8±1.0)•10^(-18) m^2/W. To our knowledge, these are the first optical limiting experiments performed at 2 ?m wavelength using CS2.
9731-19, Session 6
Tobias Baselt, Christopher Taudt, Fraunhofer IWS Dresden
(Germany) and Westsächsische Hochschule Zwickau
(Germany) and TU Dresden (Germany); Bryan Nelsen,
Westsächsische Hochschule Zwickau (Germany); Andrés-
Fabián Lasagni, Fraunhofer IWS Dresden (Germany) and
TU Dresden (Germany); Peter Hartmann, Westsächsische
Hochschule Zwickau (Germany) and Fraunhofer IWS
Dresden (Germany)
The use of supercontinuum light sources in different optical measurement methods, like microscopy or optical coherence tomography, has increased significantly compared to classical wideband light sources. The development of various optical measurement techniques benefits from the high brightness and bandwidth, as well as the spatial coherence of these sources. For some applications, only a portion of the broad spectral range
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Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV can be used. Therefore, an increase of the spectral power density in limited spectral regions would provide a clear advantage over spectral filtering.
This study describes a method to increase the spectral power density of supercontinuum sources by amplifying the excitation wavelength inside a nonlinear photonic crystal fiber (PCF). An ytterbium doped photonic crystal fiber was manufactured by a sol-gel process and used in a fiber amplifier setup as the nonlinear fiber medium. In order to characterize the fiber’s optimum operational characteristics, group-velocity dispersion
(GVD) measurements were performed on the fiber during the amplification process. For this purpose, a notch-pass mirror was used to launch the radiation of a stabilized laser diode at 976 nm into the fiber sample for pumping. The performance of the fiber was compared with a conventional
PCF. Finally, the system as a whole was characterized in reference to common solid state-laser-based photonic supercontinuum light sources. An improvement of the power density up to five times was observed between
1030 nm to 1350 nm wavelengths.
sensitive detection system. Due to the high reflectivity of the cavity mirrors, the beam experiences a long effective optical path length resulting in large absorption values and allowing to achieve detection at very low concentrations. If the mirrors reflectivity is high over a large spectral region, the technique allows the simultaneous detection of gases that exhibits absorption lines in different wavelength ranges. A supercontinuum source which possesses high brightness over a very large bandwidth and which is perfectly spatially coherent is therefore ideal to exploit the full potential of the method. Here, using a compact supercontinuum source we demonstrate for the first time multi-components gas detection of acetylene and methane with high sensitivity in the mid-infrared, over a bandwidth extending from 3000 to 3500 nm. These results are significant not only because they illustrate the potential of incoherent supercontinuum sources for spectroscopy in the mid-infrared but also because they represent the largest continuous detection window reported so far.
9731-20, Session 6
Christophe Louot, Erwan Capitaine, Badr M . Shalaby,
Katarzyna Krupa, Alessandro Tonello, Dominique Pagnoux,
Claire Lefort, Philippe Leproux, Vincent Couderc, XLIM
Institut de Recherche (France)
Coherent Raman spectroscopy methods like coherent anti-Stokes
Raman scattering (CARS) or stimulated Raman scattering (SRS) can be implemented by using a monochromatic pump wave and a broadband
Stokes wave. In the case of 1064 nm pumping, a Stokes spectrum extending up to 1600 nm is required in order to probe chemical bonds from the fingerprint area to the CH stretching region. This broadband spectrum has to be particularly flat, with the highest possible spectral power density. Usually, such spectrum is obtained by means of supercontinuum generation in a solid-core photonic crystal fiber, which is operated in the anomalous dispersion regime. Here we demonstrate all-normal dispersion supercontinuum generation in the 1080-1600 nm range by propagating sub-nanosecond pulses in a high numerical aperture standard optical fiber
(Corning HI 980, with zero dispersion wavelength at 1600 nm). The extreme saturation of the Raman gain provides a flat spectrum in the considered range, making this broadband source particularly suitable for coherent
Raman spectroscopy. The unusual regime of supercontinuum generation, i.e. Raman gain saturation regime, is highlighted. It is investigated through a complete numerical and experimental spectrotemporal study, and the corresponding results are compared with those obtained from a photonic crystal fiber. Finally the possibility of operating spectrometer-free timeresolved coherent Raman spectroscopy is introduced.
9731-21, Session 6
Caroline Amiot, Piotr Ryczkowski, Antti Aalto, Juha
Toivonen, Goëry Genty, Tampere Univ . of Technology
(Finland)
The measurement of gas concentration is paramount in many industrial applications ranging from emission control to chemical reaction optimization. Many gases of interest possess very strong absorption lines in the mid-infrared; in fact stronger than in any of other spectral regions.
Incoherent broadband cavity enhanced absorption spectroscopy is a simple and robust method for the detection of gases with high sensitivity. In this technique a broadband source is coupled to a high-finesse confocal cavity filled with gas and the transmitted light is analyzed with a wavelength-
9731-35, Session PTue
Pengxiang Liu, Wei Shi, Degang Xu, Tianjin Univ . (China);
Nasser N . Peyghambarian, The Univ . of Arizona (United
States)
We proposed a novel GaAs-based crystal fiber configuration for efficient
THz difference frequency generation (DFG), which combines the singlemode THz fiber and the quasi-phase-matching for DFG THz generation.
Calculations were performed on the characteristics of energy conversion and output beam focusing. Theoretical results indicated that the proposed
THz crystal fiber structure can provide high power and high brightness THz radiation. The output power, spectral power density and brightness are also analyzed, based on the calculation of the dynamic of energy conversion and the characteristics of the THz beam focusing. High output power (average ~1
W) and excellent focusing characteristic allow us to achieve THz generation with high brightness (100 MW/(sr•cm2)), a promising value for many applications.
9731-36, Session PTue
Thomas Schoenau, Dietmar Klemme, Romano Haertel,
Kristian Lauritsen, Rainer Erdmann, PicoQuant GmbH
(Germany)
Laser pulses from diode based laser systems in the UV range are of great interest in the fields of microscopy and spectroscopy. Providing UV wavelength pulses at variable repetition frequencies or on demand requires nonlinear frequency conversion in single pass arrangement with a crystal featuring a high effective nonlinear coefficient. In the past, such devices based on borate materials (e.g. BBO, CLBO) suffer intrinsically from walk-off due to the phase-matching condition. As a result, extensive efforts had to be made to obtain a clean transverse mode without distortion at the expense of induced power loss.
Our approach presented here utilized the newly available PP-LBGO device with 2nd-order quasi-phase matching (QPM) to obtain a walk-off free and undistorted fundamental transverse mode. We investigated and compared the conversion efficiency of PP-LBGO with a classic beta-BBO crystal and measured the beam quality. The pump laser is based on a 1064 nm distributed feedback (DFB) gain-switched seed laser diode and two-stage fiber amplifier. After second harmonic generation to 532 nm the light is focused into the PP-LBGO for single pass generation of 266 nm. Since the
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Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV
PP-LBGO is non-hygroscopic, the material is easy to handle and a long life time is expected and under investigation.
The target power level of 1 mW average power at 80 MHz is sufficient for a wide range of applications in the life sciences, such as fluorescence spectroscopy and confocal microscopy.
9731-37, Session PTue
Junji Hirohashi, Yasuhiro Tomihari, Satoshi Makio, Yasunori
Furukawa, Oxide Corp . (Japan); Marc Le Flohic, Keopsys
SA (France)
Forth harmonic (266 nm) laser was demonstrated based on pulsed fiber laser combined with frequency convertor for sensing application.
Fundamental 1064 nm laser was fiber based laser with?repetition rate of 50 kHz, peak power of 25 kW, pulse width of 1 ns and average power of 1 W.
The light was delivered by polarization maintain large mode area fiber and connected to the frequency convertor. In the frequency convertor, second harmonic 532 nm was generated by PP-Mg:SLT with more than 50% of conversion efficiency without walk-off and then forth harmonic 266 nm was generated by BBO with 30% of conversion efficiency. Both frequency conversion devices were operated at 40 degree-C. The 266 nm with average power of more than 150 mW was confirmed with stable operation. Since the output properties of relatively high repetition rate and high peak power, it is suitable for sensing application from the point of better signal noise ratio and measurement speed. In addition, since the combination of this fiber laser head and frequency convertor with simple single pass configuration, it is possible to realize affordable laser module for easy to integrate into the portable sensing system such as LIDAR systems. The shorter wavelength such as 266 nm could be attractive to characterize much smaller particle sensing comparing to the visible or IR sensing systems.
9731-39, Session PTue
Julian M . Estudillo-Ayala, Jose D . Filoteo-Razo, Juan
Carlos Hernández-Garcia, Univ . de Guanajuato (Mexico);
Jesus Pablo Lauterio-Cruz, Ctr . de Investigaciones en
Óptica, A .C . (Mexico); Daniel Jáuregui-Vázquez, Univ . de Guanajuato (Mexico); Baldemar Ibarra-Escamilla,
Instituto Nacional de Astrofísica, Óptica y Electrónica
(Mexico); Oliver J . M . Pottiez, Ctr . de Investigaciones en
Óptica, A .C . (Mexico); Roberto Rojas-Laguna, Univ . de
Guanajuato (Mexico); Evgeny A . Kuzin, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico)
In this work we show the changes of polarization at different wavelengths in the end of a photonic crystal fiber (PCF) by means bandpass filters in a supercontinuum light source. A linear and circular polarization was introduced in a piece of PCF, showing the changes of the polarization for each wavelength of each one of the filters from 450 to 700nm. We used a microchip laser as pumping source with wavelength of 532nm and short pulses least than 1 ns with repetition rate of 9KHz. We obtained a continuous spectrum in the visible spectral region. We show a comparison of the polarization state at the fiber input with respect to polarization state in the fiber output for different wavelengths by rotating the axes of the PCF.
9731-40, Session PTue
Marcel Braune, Martin Maiwald, Bernd Sumpf, Günther
Tränkle, Ferdinand-Braun-Institut (Germany)
9731-38, Session PTue
Jie Zang, Zhenhua Cong, Xiaohan Chen, Xingyu Zhang,
Zengguang Qin, Zhaojun Liu, Jianren Lu, Shandong Univ .
(China); Shiqi Jiang, Shandong Univ . (China); Qiang Fu,
Dong Wu, Shandong Univ . (China)
The stimulated polariton scattering (SPS) is a nonlinear process in which the second- and third-order nonlinear effects are involved. The essential condition for SPS in a crystal is the existence of one or more intense transverse optical A1 modes which are both infrared- and Raman-active.
In the process of the SPS, three waves including the pumping wave, the generated Stokes wave and the polariton wave interact in the overlapped beam area. The momentum conservation and energy conservation must be satisfied simultaneously. The SPS can be used to generate tunable terahertz wave and tunable Stokes laser emission near the pumping wavelength. SPS can occur in a few crystals. Potassium titanyl arsenate (KTiOAsO4, KTA) is one of them.
This paper presents the tunable Stokes laser characteristics based on the
SPS in KTA crystal. The pumping source is a 1064.2 nm Q-switched laser.
The pulse energy, pulse width, repetition rate and beam size are 125 mJ, 10 ns, 10 Hz and 3.5 mm, respectively. The tenability is realized by adjusting the angle between the pumping beam and the Stokes laser cavity axis. When the angle is changed from 1.875° to 6.500°, five tunable ranges from 1077.9 to 1079.0 nm, from 1080.1 to 1080.8 nm, from 1082.8 to 1083.6 nm, from
1085.5 to 1085.8 nm, from 1086.8 to 1088.4 nm are obtained. The maximum pulse energy is 24.7 mJ obtained at the wavelength of 1078.6 nm.
Raman spectroscopy in the visible spectral range is of great interest due to resonant enhancement of signals in organic samples. Nevertheless, fluorescence and background signals can mask these lines. Shifted
Excitation Raman Difference Spectroscopy is a potential tool to overcome this distortion. To apply this method, a dual wavelength light source is necessary. The distance between these two wavelengths should be approximately the spectral width of the bands under study.
In this work, a micro-integrated SHG light source emitting at 488 nm with a continuous tuning range up to 2 nm (83 cm-1) and without moving parts is presented. With this feature the SERDS distance between the excitation wavelengths can be adjusted according to the target.
The pump source, a DFB laser emitting at 976 nm, and a PPLN waveguide crystal are directly mounted on a micro-Peltier-element. Due to the comparable temperature tuning of laser (66 pm/K) and crystal (72 pm/K), by changing the common temperature from 15°C to 72°C and slight adjustment of laser current (4 pm/mA), the above mentioned tuning range is achieved. An approximately constant 488 nm output power of about 27 mW was measured over the whole spectral range. At lower temperatures, the output power reaches 30 mW. With increasing temperature due to the decrease of the pump power, the SHG power deteriorates with -0.1 mW/K.
Moreover, the concept delivers a suppression of the amplified spontaneous emission by the SHG crystal. The use of bandpass-filters is therefore not necessary. A wider SERDS distance becomes easily feasible.
92 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV
9731-41, Session PTue
µ
Kiyoshi Kato, Chitose Institute of Science and Technology
(Japan); Valentin P . Petrov, Max-Born-Institut für
Nichtlineare Optik und Kurzzeitspektroskopie (Germany);
Nobuhiro Umemura, Chitose Institute of Science and
Technology (Japan)
Although we reported the Sellmeier equations for GaSxSe1-x (x=0, 0.09,
0.40, and 1.0) that provide excellent reproduction of the phase-matching conditions for harmonic generation of a CO2 laser at 10.5910
µ m [Kato and
Mikami, Appl. Opt., 53, 2177(2014)], the birefringence of GaSe and GaS at
1THz given by these Sellmeier equations are about 0.38 and 0.34 smaller than the experimental values of Zhang et al. [J. Appl. Spectroscopy, 77,
850(2011)] and Molloy et al. [CrystEngComm., 16, 1995(2014)], respectively.
In order to construct the accurate Sellmeier equations for GaSxSe1-x in the THz range, we measured the phase-matching angles for type-2 DFG between a Nd:YAG laser and BBO/OPO in a c-cut 4.7-mm-thick GaS0.4Se0.6 crystal at 100.4-1030.6
µ m. These data were used to refine the Sellmeier equations for GaSxSe1-x in the THz range.
By using these Sellmeier equations for GaSxSe1- x (0?x?0.40), we calculated the phase-matching conditions for the near-IR to THz frequency conversion achieved by Nazarov et al. [Appl. Phys. Lett., 99, 081105(2011) and 100,
136104(2012)]. For GaS0.29Se0.71 pumped by a Ti:Al2O3 laser at 0.797
µ m, our index formula gives the type-1 phase-matching angle of ?ext=7.86º for generating the 1.8THz radiation, which agrees well with their experimental value of ?ext=8º.
While, for the same crystal pumped at 0.790
µ m, our formula gives the eee-type phase-matching angle of??ext=45.0º for generating the 1THz radiation and the refractive index mismatch of |ne, gr(?, ?)-ne(?, ?)|=0.1096, which agree with their experimental values of ?ext=45º and |ne,gr(?, ?)-ne(?,
?)|=0.12.
Thus, the utility of our Sellmeier equations for GaSxSe1-x is demonstrated.
9731-42, Session PTue
Alexandre S . Shcherbakov, Adan O . Arellanes, Instituto
Nacional de Astrofísica, Óptica y Electrónica (Mexico) performed with a specially designed wide-aperture acousto-optical cell made of the calomel (?-Hg2Cl2) crystal, are presented. The obtained spectral resolution ~0.235 Å at 405 nm (i.e. the resolving power ~17,200) can be compared with the most advanced acousto-optical spectrometers for space/airborne operations. Evidently, our results with the calomel-based acousto-optical cell look like the best we can mention at the moment.
9731-43, Session PTue
Alphonse L . Rasoloniaina, Rodolphe Collin, Christelle
Pareige, Ecole Nationale Supérieure des Sciences
Appliquées et de Technologie (France); Stéphane Balac,
Univ . de Rennes 1 (France); Thierry Chartier, Ecole
Nationale Supérieure des Sciences Appliquées et de
Technologie (France); Pascal Besnard, CNRS-Fonctions
Optiques pour les Technologeis de l’information (France);
Alain Mugnier, David Pureur, Quantel Group (France)
High-power green lasers present a great interest for many applications such as DNA sequencing, ophthalmology, biotechnology or laser Doppler velocimetry. Second-harmonic generation (SHG) based on quasi-phase matching (QPM) technique presents some advantages such as compactness, high conversion efficiency and high beam quality. In QPM technique, a precise control of crystal temperature is required to obtain the optimum conversion. However, for high powers, thermal effects due to fundamental harmonic (1064 nm) absorption, second harmonic (532 nm) absorption and green induced infrared absorption (GRIIRA) become non-negligible.
Temperature gradient takes place and leads to a local variation of the index of refraction. The phase matching becomes temperature dependent and this limits the efficiency. In this case, an active temperature control of the crystal is needed to compensate this phenomenon. In this work, we propose both theoretical and experimental studies of continuous-wave second-harmonic generation in a periodically-poled congruent lithium niobate crystal doped with a magnesium oxide crystal (MgO:PPLN). The temperature distribution in the crystal is obtained by solving: (i) the propagation equations for the fundamental harmonic and second harmonic by a split-step Fourier method and (ii) heat transfer equation by finite elements method where the longitudinal and transverse variations of temperature are taken into account. We present a comparison between theoretical simulations and experimental results. A good agreement with the experiment is observed in term of temperature acceptance or temperature control. Second harmonic generation up to 2.5 W of output power is achieved in 25 mm long crystal.
9731-44, Session PTue
Han Li, Joseph W . Haus, Partha P . Banerjee, Univ . of Dayton
(United States)
Principally new features of the non-collinear two-phonon light scattering governed by elastic waves of finite amplitude in birefringent bulk crystals are detected and observed. The main goals of our investigations are to reveal novel important details inherent in the nonlinearity of this effect and to study properties of similar parametric nonlinearity both theoretically and experimentally in wide-aperture crystals with moderate linear acoustic attenuation. An additional degree of freedom represented by the dispersive birefringence factor, which can be distinguished within this nonlinear phenomenon, is characterized. This physical degree of freedom gives us a one-of-a-kind opportunity to apply the strongly non-linear two-phonon light scattering in practice for the first time. The local unit-level maxima in the distribution of light scattered into the second order appear periodically as the acoustic power density grows. It makes possible to identify a few transfer function profiles peculiar to these maxima in the isolated planes of angular-frequency mismatches. These maxima give us an opportunity to choose the desirable profile for the transfer function at the fixed angle of incidence for the incoming light beam with a wide spectrum .The needed theoretical analysis is developed and proof-of-principle experiments,
We examine the problem of third-harmonic generation (THG) in a thin film stack fabricated from multiple layers of metal and dielectric thin films, also called a metallodielectric [1]. We apply the transfer matrix method extended to cover obliquely incident fields [2] to the problem of third-harmonic generation. Due to interference and evanescent field penetration through the metal layers the transmission is much higher than for a single thick metal film.
Specifically, we examine THG using silver layers sandwiched between a relatively high index dielectric (around a value of 2), such as tantalum pentoxide or zinc oxide. The THG simulations are an extension of the method developed in Ref. [2] where second-harmonic generation was examined. In the metallodielectric case we use realistic dielectric materials
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data and a complex third-order nonlinear coefficient of the metal. The reflected and transmitted third-harmonic efficiencies are optimized by varying each layer thickness within experimentally reasonable limits and by changing the angle of incidence of the pump wave.
Further THG metallodielectrics using metals such as copper and gold, as well as selected dielectric materials, will be examined using the same methodology. The comparison between the various metallodielectrics will be made with recommendations for experimental studies.
9731-45, Session PTue
Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV
Dmitry E Milovzorov, Fluens Technology Group Ltd .
(Russian Federation) nonlinear processes at lower densities that compromise energy coupling or cause energy deposition in undesirable locations. Dominant processes are scattering on ion-acoustic waves (Stimulated Brillouin Scattering), scattering on electron-plasma waves (Stimulated Raman Scattering), or two-plasmon decay. These are complex instabilities that require advanced computer simulations even for approximate predictions of the problems being caused by them.
We will discuss laser-plasma instabilities (LPI), measurement techniques such as near beam imaging, and methods to minimize these instabilities using beam smoothing techniques. Measurements for various levels of LPI will illustrate the progress made at Sandia in order to advance the efforts in magneto-inertial fusion.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed
Martin Corporation, for the U.S. Department of Energy’s National Nuclear
Security Administration under contract DE-AC04-94AL85000.
Resonant second-harmonic generation by nanocrystalline silicon films was studied by using optical spectroscopy for a different polarization schemes for incident laser and output radiation. The morphology of films is different for any of them: rectangular crystals in the film with average nanocrystals size 9.7 nm and irregular for the film with nanocrystal size 16.1 nm. There is a differences in resonant spectral peaks positions: 3.22 eV and 3.31 eV for the silicon film with nanocrystal size 9.7 nm; and 3.2 eV and 3,26 eV for the silicon film with nanocrystal size 16.1 nm. SHG spectra show the resonance sharp peaks which is related to the defect or surface states in band gap of silicon. From the rigid surface the optical nonlinear response on second harmonic can be described as stochastic value that can be estimated as nonlinrar function of fundamental laser intensity multiplied on coefficient on nonlinear transformation of radiation and correlation function between added field fractions generated by various parts of rigid films.
9731-23, Session 7
Sergey A . Babin, Ekaterina A . Zlobina, Sergey I . Kablukov,
Evgeniy V . Podivilov, Institute of Automation and
Electrometry (Russian Federation)
9731-22, Session 7
(Keynote
Presentation)
Matthias Geissel, Adam J . Harvey-Thomson, Thomas J .
Awe, Sandia National Labs . (United States); Michael E .
Campbell, Lab . for Laser Energetics (United States);
Matthew R . Gomez, Eric Harding, Christopher Jennings,
Mark W . Kimmel, Patrick F . Knapp, Sandia National Labs .
(United States); Sean M . Lewis, The Univ . of Texas at Austin
(United States); Kyle Peterson, Marius Schollmeier, Adam
B . Sefkow, Jonathon E . Shores, Daniel B . Sinars, Stephen A .
Slutz, Ian C . Smith, Christopher S . Speas, Roger A . Vesey,
John L . Porter, Sandia National Labs . (United States)
Random Raman lasers attract now a great deal of attention as they operate in non-active turbid or transparent scattering media. In the last case, singlemode fibers with feedback via Rayleigh backscattering are used to generate high-quality directed laser beam with relatively narrow modeless spectrum.
However, generation in such random Raman fiber lasers (RRFLs) is limited in polarization properties: the light is usually depolarized or has unstable polarization, even for the first Stokes wave.
Here we demonstrate a linearly-polarized cascaded random Raman lasing in a PM fiber with polarized pumping. Quantum efficiency of converting input pump radiation (1.05?m) into the 1st (1.11?m), 2nd (1.17?m) and 3rdorder (1.23?m) Stokes waves amounts to 79%, 83%, and 77%, respectively.
Taking that the passive losses at propagation of pump radiation in the fiber are ~15%, almost all pump photons are converted into the generated Stokes wave, regardless of the order. Herewith, polarization extinction ratio (PER) is as high as >22 dB for all the waves at powers up to ~10 W. The laser bandwidth grows with increasing Stokes order, but it is almost independent on the generated power varying in the range of 0.8-1.3nm, 1.4-2.3nm and
2.4-3.3nm for the consecutive orders, respectively. At that, the generated spectrum remains to be sufficiently narrower than the Raman gain profile.
An analytical model has been developed describing well the generated power and spectrum for all components of the cascaded RRFL. The unique features of such source with a potential of broad-range tuning offer new opportunities in applications.
Sandia National Laboratories pursues a novel concept of inertial confinement fusion that includes a pre-magnetization of the fuel. The
‘Magnetized Liner Inertial Fusion’ concept heats up deuterium untilizing the Z-Beamlet laser while exposed to a magnetic field and subsequently implodes fuel using the ‘Z’ pulsed power facility.
While the interaction of lasers with matter is well understood for processes at kilowatt power levels, the pre-heat process in MagLIF reaches terawatt powers and intensities beyond 10^14 W/cm?, which are subject to complex and largely nonlinear phenomena.
A thin solid density window covers the laser entrance hole to confine the fuel initially, and a pre-pulse decompresses it below the critical plasma density, enabling propagation into the fuel. However, there are
9731-24, Session 7
Victor L . Lambin-Iezzi, Ecole Polytechnique de Montréal
(Canada); Thomas F . S . Büttner, Ctr . for Ultrahigh bandwidth Devices for Optical Systems (Australia);
Amirhossein Tehranchi, Sébastien Loranger, Ecole
Polytechnique de Montréal (Canada); Irina V . Kabakova,
Benjamin J . Eggleton, The Univ . of Sydney (Australia);
Raman Kashyap, Ecole Polytechnique de Montréal
(Canada)
94 SPIE Photonics West 2016 · www.spie.org/pw
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We have investigated hybrid Multi-Wavelength Brillouin and erbium fiber lasers (MWBEFL) which are particularly interesting because of their simplicity, robustness, their only need for components, low power threshold, high tunability and their ability to generate a large number of
Brillouin shifted frequencies. Their basic principle is to combine the narrow nonlinear gain offered by SBS in an undoped fiber with the broadband linear gain from an erbium doped fiber to enable the cascaded process of SBS.
These lasers represent a convenient way for generating multi-wavelengths with comb-like optical spectra that have a frequency channel spacing equal to the Brillouin frequency shift ~10 GHz or multiple of it. Numerous configurations for MWBEFLs have been suggested over the years, but their characterization has been limited to optical and radio-frequency spectral measurements. Here, we provide a detailed temporal characterization of several MWBEFL configurations by measuring the optical power of the single frequency channels with high temporal resolution. It is found that the power in each channel is highly unstable due to the excitation of several cavity modes. We also provide real-time measurements for a configuration that was reported to emit phase-locked picosecond pulse trains, concluded from autocorrelation measurements [1]. The real-time measurements reveal a high degree of instability without the formation of stable pulse trains.
References:
[1] S. Loranger, V. L. Iezzi, and R. Kashyap, “Demonstration of an ultra-high frequency picosecond pulse generator using an SBS frequency comb and self phase-locking,” Opt. Express, vol. 20, pp. 19455-19462, 2012.
9731-25, Session 7
Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV
Schadrac Fresnel, Stéphane Trebaol, Yohann Léguillon,
Christelle Pareige, Pascal Besnard, Ecole Nationale
Supérieure des Sciences Appliquées et de Technologie
(France); Sophie LaRochelle, Univ . Laval (Canada)
Compact and low-cost coherent sources are needed to improve system performances of sensors and telecommunication systems, e.g. in coherent optical communication links and microwave photonic applications. Brillouin fiber lasers (BFLs) have been attracting a lot of interest lately due to their very narrow linewidth and very low relative intensity noise (RIN) and frequency noise (FN). Indeed, the first Stokes component (S1) generated by a pump can have more than 6 dB RIN-reduction compared to the pump.
Furthermore, its FN can be reduced by 10-20 dB, depending on the pump characteristics and on the packaging of the Brillouin laser. We have already shown an 8 dB reduction (above the theoretical 6 dB-limit) in S1-RIN using a compact chalcogenide BFL with two Stokes orders. This can be explained by the fact that, above the second order threshold, the lasing S1 component is saturated leading to a compression of its intensity noise. In this paper we examine robust and compact silica BFLs with improved noise properties.
Since single frequency operation is mandatory to achieve coherent sources, the Free Spectral Range of the laser cavity has to be higher than the
Brillouin gain-bandwidth or, in other words, a short cavity length has to be employed (< 20 m). We designed a 16.66 m-long polarization-maintaining silica-fiber cavity (FSR = 12 MHz) with a 10 dBm threshold for S1, 15 dBm for the second-order component S2, and 18 dBm for S3. Operating above the S2 threshold, we show a severe damping of the S1 RIN of 20 dB, while maintaining a FN reduction of 10 dB, compared to that of the pump.
laser is demonstrated. Average output power level of 1.25 W is generated at the first Stokes wavelength of 2602 nm for 9.7 W incident pump power.
Output pulse widths as short as 19 ns was measured at a repetition rate of
6.67 kHz. Near-diffraction limited beam quality is observed (M2=1.25). This simplified Raman laser configuration can harness the high average power levels offered by Thulium- and Holmium-doped solid-state and fiber lasers to generate fixed-wavelength and tunable output at 2.3-2.8 um.
9731-27, Session 8
(Invited
Paper)
Alexander V . Sergienko, Boston Univ . (United States)
Integrated optics based on lithium niobate offers the versatility of multifunctional devices connected by channel waveguides on a single substrate.
The enabling technology is the diffusion of lithographically defined titanium stripes into lithium niobate resulting in the formation of low loss channel waveguides. Combined with quasi-phase matching induced by electric field poling this leads to non-linear frequency convertion of exceptional efficiency. The distinct advantage of Ti in-diffused waveguides is that both
Type I and Type II phase matching processes are allowed by a suitable choice of the poling period. Moreover, the low optical background facilitates the quantum frequency conversion of polarization-encoded photonic qubits with high fidelity. The careful design of poling period together with the waveguide geometry allows controlling the transverse mode structure of the qubits. Additional flexibility in the poling profile design permits the tailoring of phase matching spectrum. A quasi-rectangular flat-top or Gaussian spectrum as broad as 200 nm is designed by chirping and apodization of the poling period. We discuss applications of such devices to quantum frequency conversion of temporal qdits, which has been proposed for higher dimensional encoding of quantum information, and mid-infrared chip-scale frequency combs generation by frequency down conversion of commercially available Er combs at 1550 nm. Additional constraints imposed on quasi-phase matching would allow control over spectral phase as well. We discuss extended phase matching conditions in the context of generating frequency-correlated photon pairs by spontaneous parametric down conversion.
9731-28, Session 8
Sarah-Katharina Meisenheimer, Univ . of Freiburg
(Germany) and Fraunhofer-Institut für Physikalische
Messtechnik (Germany); Josef U . Fürst, Univ . of Freiburg
(Germany); Annelie Schiller, University of Freiburg
(Germany); Karsten Buse, Fraunhofer-Institut für
Physikalische Messtechnik (Germany) and Univ . of Freiburg
(Germany); Ingo Breunig, Univ . of Freiburg (Germany)
9731-26, Session 7
Onur Kuzucu, ASELSAN Inc . (Turkey)
An external cavity BaWO4 Raman source pumped by a Q-switched Ho:YAG
Optical parametric oscillators (OPOs) provide tunable continuous-wave coherent light for, e.g., infrared spectroscopy. In such current OPO-based systems, typically light of a pump laser with a wavelength of about 1 µ m is down-converted by a periodically-poled lithium niobate crystal placed inside a mirror cavity. Whispering gallery resonators (WGRs) are promising cavities for miniaturizing the current OPO setup. However, identification of the whispering gallery modes and controlled tuning of wavelengths over a wide spectral range are essential and still challenging for employing
OPOs in WGRs for infrared spectroscopy. In this work, we demonstrate that identification of the whispering gallery modes of pump, signal, and idler light can be achieved by comparing experimental data to simulations
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Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV for both, the pump spectrum and the tuning behavior of the OPOs. For controlled tuning of the output wavelengths over a wide infrared spectral range (1.7–2.5 µ m), a whispering gallery pump mode with selected radial and polar mode numbers is addressed. The pump wavelength and these mode numbers are kept fixed while increasing the temperature of the crystal in well-defined steps, going from one longitudinal mode to the next. This provides wider and more reliable tuning than it has been achieved before.
Experimental data showing mode identification, improved tuning and the applicability to spectroscopy are presented for a calligraphically poled WGR with 2 mm diameter and 28 µ m domain period length, being suitable for quasi phase matching of 1.04 µ m pump light. of average power at 2039 nm by using a reflective Volume Bragg Grating
(VBG). Devices such as piezo-controlled etalons can provide rapidly tunable, narrow-linewidth power from this system.
9731-31, Session 9
(Invited Paper)
Christian Pedersen, Peter Tidemand-Lichtenberg, Technical
Univ . of Denmark (Denmark)
9731-29, Session 8
Rita D . Peterson, Gary Cook, Air Force Research Lab .
(United States)
Coherent sources that are broadly and continuously tunable in the mid- and longwave infrared are of interest for a variety of scientific, commercial, and military applications. The advantages in an OPO of quasi-phasematched materials like orientation-patterned gallium arsenide (OPGaAs) come at the cost of the angle tuning possible in birefringent nonlinear crystals.
Temperature tuning is limited by the material’s dn/dT value, and lacks speed and stability. A better alternative is to tune the OPO by tuning the pump laser.
Here we report an OPGaAs OPO pumped by a gain-switched Cr:ZnSe laser which was continuously tuned by an intracavity etalon. The etalon also narrowed the output linewidth to 2 nm. The Cr:ZnSe laser operated at a repetition rate of 500 Hz with a 25 ns pulsewidth. The pump was focused to a spot size (1/e^2) of 100 µ m at the center of a simple linear resonator formed by two 5-cm ROC mirrors. The OPGaAs crystal was 14 mm long, with a period of 97 µ m, and was mounted with no active cooling. Tuning the pump laser over a range of 90 nm (2385-2475 nm) produced OPO output over a range of almost 4.5 µ m (3500-7450 nm). OPO tuning was ultimately limited by coatings on the crystals and the resonator mirrors, as the Cr:ZnSe laser is capable of much broader tuning as a pump source. A maximum slope efficiency of 21% was obtained, with a pulse energy threshold of 93 µ J.
9731-30, Session 8
Yelena Isyanova, Wenyan Tian, Q-Peak, Inc . (United
States); Peter F . Moulton, MIT Lincoln Lab . (United States)
Mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) electromagnetic radiation spanning the 3-8 µ m and 8-15 µ m range, respectively, is important for a range of spectroscopic applications. A first aspect hereof is that the 3-15 µ m range covers the fundamental absorption band of nearly all gasses AND bear specific vibrational chemical signature of molecules; a key to new spectroscopy, chemical sensing and identification.
The 3-15 µ m wavelength region is therefore also a part of the so called
“fingerprint” region. A second aspect relates to the 3-5 µ m and 8-13
µ m atmospheric “transmission windows” enabling applications such as environmental gas monitoring (e.g. CH4, NOx, SOx and CO2), thermal (heat) radiation and remote sensing (stand of detection). Other examples are food analysis and cancer research. The exploitation of MWIR and LWIR therefor holds great promises for science, society and industry.
A major challenge for exploitation of this highly preferred optical mid-
IR band has been severe technological challenges related to low-noise detection and imaging. We suggest nonlinear upconversion, using diodepumped solid state laser technology, followed by visible light detection, to demonstrate low noise detection and mid-IR imaging for a range of applications, even at room temperature.
Theoretical and technological aspects of upconversion for detection and imaging will be presented as well as relevant mid-IR applications for gas sensing and analysis of complex molecules.
9731-32, Session 9
Carlo Vicario, Paul Scherrer Institut (Switzerland); Gunnar
Arisholm, Norwegian Defence Research Establishment
(Norway); Christoph P . Hauri, Paul Scherrer Institut
(Switzerland) and Ecole Polytechnique Fédérale de
Lausanne (Switzerland); Balazs Monoszlai, Paul Scherrer
Institut (Hungary) and Univ . of Pécs (Hungary)
We report here on the performance of a narrow-line, mid-IR source based on a PPLN-crystal optical parametric generator (OPG). The PPLN crystal was pumped by a pulsed, 20-MHz-rate, 1064-nm Yb:fiber-based source operating with 20-psec pulses and average output power of 20 W. Prior to achieving the parametric generation, we built an optical parametric amplifier
(OPA). We used a 2051-nm diode with output power of 0.8 mW as a seed source for the OPA. The 2-cm long PPLN crystal with the 31.1 ?m poling period was placed in a high-temperature oven at 137 deg. C. We achieved the OPA and OPG threshold at 17 W and 18 W of pump power, respectively.
Since the average output power of the OPG was low, we replaced the 2-cm crystal with the 5-cm one with the same grating period. With this crystal, the OPG threshold was observed at 5.2 W of pump power. Seeding was not necessary and did not affect the performance of the OPG. The maximum output power measured was 0.55 W.
The OPG produced a broad spectrum between 2027 nm and 2239 nm.
Since we were interested in producing a narrow, <1 nm linewidth output, we placed a band-pass filter after the OPG that allowed us to select a 30 nm bandwidth output. We achieved further line reduction (0.7 nm) and 4.5 mW
Infrared pulses with large spectral width and wavelength extending from
1.2 to 3.5 µ m are generated by multiple nonlinear processes in thin organic crystal DAST (4-N, N-dimethylamino-4’-N’-methylstilbazolium tosylate). In the experiment, the crystal is pumped by an optical parametric amplifier delivering few mJ, 65 femtosecond pulses at a central wavelength of 1.5
µ m. A net redshift of the input wavelengths and a spectral width up to
1.5-octave are achieved when the DAST is pumped at fluence larger than 10 mJ/cm 2. The compact experimental setup provides spectrally broadened pulse with energy up to 700 ?J and conversion efficiency of 25 %. Scaling the pulse energy up to several mJ is feasible with a larger DAST crystal and higher pump energy at constant pump fluence. The results are qualitatively reproduced by numerical simulations, which provide an explanation to the spectral broadening process and accounts for the asymmetric broadening towards longer wavelength. The presented effect is ascribed to cascaded second order processes mediated by the exceptionally large effective ?2 nonlinearity of DAST, but the shape of the spectrum indicates that a delayed
?3 process may also be involved. Further studies to investigate the temporal compression of the multi-octave spectra presented here are ongoing.
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Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV
9731-33, Session 9
Ameneh Bostani, Amirhossein Tehranchi, Raman Kashyap,
Ecole Polytechnique de Montréal (Canada)
Generation of broadband spectra centered at short wavelengths around
775 nm has applications in biomedicine and spectroscopy. Up-conversion techniques such as second harmonic and sum frequency generation exploiting lasers in the communication band provide coherent radiation in short wavelengths. Nonlinear materials such as periodically poled lithium niobate (PPLN) have been extensively researched for this purpose due to several advantages . However, PPLN cannot work for simultaneous SHG and SFG due to its narrow bandwidth for a reasonable efficiency. Also, as the effective period of PPLN changes by angular rotation and temperature, fine alignment and controlled temperature are required to produce the maximum efficiency for a designed wavelength. However, aperiodically poled nonlinear materials in the form of chirped and step-chirped (SC) gratings are proposed for broadband up-conversion to solve these problems . Moreover, high-power CW fiber lasers with a broader bandwidth compared to monochromic sources are available at many wavelengths including the C-band. Therefore, one can benefit from larger conversion bandwidth of SHG and SFG besides temperature-insensitivity of SC-PPLN and simultaneously up-convert the wavelengths of available fiber lasers.
Here, we use a high-power fiber laser, an amplified narrowband laser and an
SC-PPLN to simultaneously generate SF and SH using the entire spectrum of the fiber laser. The input spectrum depicts the high-power (25 W) laser and the narrowband laser operating around 1550 nm and 1555 nm, respectively.
The output spectrum illustrates the simultaneous broadband SHG of the high-power laser around 775 nm and broadband SFG around 776.5 nm
9731-34, Session 9
Brett H . Hokr, Texas A&M Univ . (United States); Marlan
O . Scully, Texas A&M Univ . (United States) and Baylor
Univ . (United States) and Princeton Univ . (United States);
Vladislav V . Yakovlev, Texas A&M Univ . (United States)
Anderson localization, also known as strong localization, is the absence of diffusion in turbid media resulting from wave interferences. The effect was originally predicted for electron motion, and is widely known to exist in systems of less than 3 dimensions. However, Anderson localization with photons in 3 dimensional systems remains an elusive and controversial topic. Random Raman lasing offers the unique combination of large gain and virtually zero absorption. The lack of absorption makes long path length, localized modes possible and the presence of gain offsets what little absorption is present, and preferentially amplifies localized modes due to their large Q factors compared with typical low Q modes present in complex media. Random Raman lasers exhibit several experimentally measured properties that diverge from classical, particle-like, diffusion.
First, the temporal width of the emission being 1 to a few nanoseconds in duration when it is pumped with a 50 ps laser is a full order of magnitude longer than is predicted by Monte Carlo simulations. Second, as the sample thickness is increased from 1 mm to 10 mm, the lasing threshold is decreased by 20%. Monte Carlo simulations and a coupled diffusion equation model both predict only a negligible change as the sample is increased from about
1000 transport mean free paths to 10,000. We will highlight these clear divergences from particle-like behavior, which can only be explained by the presence of high-Q localized modes consistent with Anderson localization.
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9732-1, Session 1
Daniel R . Solli, Bahram Jalali, Univ . of California, Los
Angeles (United States)
Analog computing machines replicate the dynamics of an inaccessible problem with a tractable, user-controlled system. These devices have been employed in the form of geared mechanisms for astronomical computations since antiquity, while more modern examples include mechanical systems for gun-fire control and general-purpose calculation machines based on analog electronics. The rise of digital machines and advanced algorithms has rendered these analog machines largely obsolete. Nevertheless, computation time and accuracy remain limiting factors for simulations of complex dynamics, which are known for their dramatic sensitivities to initial conditions and diverse solution spaces. We discuss the concept of optical computing not as a replacement for digital machines but as an analog hardware accelerator. Optical co-processors offer a means to address computational challenges in nonlinear dynamics. Specifically, rapidlyevolving optical systems coupled with advanced real-time measurement techniques can be harnessed to generate massive amounts of complex data
(aka big data) that would take an electronic digital computer far longer to simulate (by many orders of magnitude). Previous interest in optical computing has been directed at mirroring digital electronics, an effort challenged by the lack of an efficient, compact switch. In contrast, optical hardware accelerators are a move in a different direction, which is already meeting with success.
9732-2, Session 1
(Invited Paper)
Georg Herink, Claus Ropers, Georg-August-Univ .
Göttingen (Germany); Bahram Jalali, Univ . of California,
Los Angeles (United States); Daniel R . Solli, Univ . of
California, Los Angeles (United States) and Georg-August-
Univ . Göttingen (Germany)
Passive mode-locking forms the basis of today’s ultrafast science and technology. Mode locking is a complex process, and once established, it is remarkably robust and stable. In contrast, the transition to mode locking is highly stochastic and remains difficult to study experimentally despite the technological maturity of modern sources. Conventional forms of measurement are generally not suitable for capturing such rapid, nonrepetitive phenomena. Moreover, the timescales involved span many orders of magnitude from a single cavity roundtrip of nanosecond duration up to many thousands of roundtrips (milliseconds). Here, we present real-time spectroscopy of the transition to the mode-locked state in a
Kerr-lens mode-locked titanium-sapphire (20-fs) oscillator over 900,000 consecutive periods. These experiments are enabled by the mapping of spectral information to the time domain via the dispersive Fourier transform, utilizing group-velocity dispersion and a real-time oscilloscope.
We resolve the dynamics over the entire buildup, observing characteristic features on various timescales. The onset of mode-locking begins from a random mixture of quasi-continuous waves, milliseconds before the actual establishment of a femtosecond pulse. Yet, the most rapid spectral broadening, along with marked wavelength shifts, occurs within a few hundred roundtrips. In addition, we observe transient mode beatings that can be employed as a time-resolved probe of the dynamic intracavity nonlinearity. These results lend new insights into the mode-locking transition and illustrate the utility of real-time spectroscopy as a diagnostic tool for ultrashort sources.
9732-3, Session 1
Miro Erkintalo, Antoine F . J . Runge, Neil G . R . Broderick,
The Univ . of Auckland (New Zealand)
A soliton explosion is a dramatic effect, whereby a pulse circulating in a mode-locked laser undergoes a sudden structural collapse, yet remarkably recovers its original shape within a few roundtrips. Our group recently reported the first observation of such explosions in a fibre laser. Here, we expand on our initial work, reporting a detailed numerical and experimental study of the dynamics and characteristics of soliton explosions.
Our experiment is based on a passively mode-locked Yb-doped fibre laser, in which explosions occur close to the boundary between stable and noise-like operation. To capture the events, we use the dispersive Fourier transformation to record, in real time, the pulse-to-pulse spectra of the laser.
We explore a variety of operating conditions by systematically adjusting the laser pump power and its cavity length. We also use a realistic model based on a set of generalized nonlinear Schrodinger equations to simulate the explosion dynamics.
We find that the explosion dynamics are strongly influenced by the operating conditions. As a general trend, the frequency of the events increases as the laser’s parameters move closer towards the boundary of unstable operation. In fact, when sufficiently close to that boundary,
“explosions” can even become more frequent than ordinary pulses.
Moreover, our simulations reveal that complex features in the spectral and temporal profiles of the explosion events can be explained in terms of a multi-pulsing instability. Our results provide new insights into the nature of soliton explosions, elucidating the processes that underpin the destabilization of passively mode-locked lasers.
9732-4, Session 1
(Invited
Paper)
Günter Steinmeyer, Simon Birkholz, Max-Born-Institut für
Nichtlineare Optik und Kurzzeitspektroskopie (Germany);
Carsten Brée, Weierstrass-Institut für Angewandte Analysis und Stochastik (Germany); Ayhan Demircan, Leibniz Univ .
Hannover (Germany)
The discovery of optical rogue waves initiated a new direction of research, aiming at finding common patterns and similar mechanisms in the emergence of extreme-value statistics across a variety of completely different physical systems. While the ubiquity of the rogue waves is certainly interesting all by itself, the usefulness of this universal concept has to be ultimately gauged by resulting advance in understanding and predicting ocean rogue waves. To this end we performed an analysis of ocean rogue wave records and time series of optical rogue waves. Our analysis is based on nonlinear time series analysis, in particular the Grassberger-
Procaccia algorithm (GPA), and clearly indicates that rogue wave dynamics may emerge due to two different scenarios. Only in case of a quantum mechanical origin, the resulting rogue waves are completely unpredictable and appear without a warning. However, if the underlying physics is
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Conference 9732: Real-time Measurements,
Rogue Events, and Emerging Applications ultimately turbulence, as in the ocean, rogue waves bear a surprising amount of predictability.
Moreover, our analysis reveals that nearly all aspects of ocean rogue waves can be explained by linear interference of a small but variable number of elementary waves. Investigating the resulting probability density functions in this situation, it appears striking that rogue waves can only form when at least 10 waves of equal amplitude interfere. At larger numbers, the formation of rogue waves grows rapidly and exceeds all unconditional global estimates by factors of ten and more. Finally, GPA offers a unique opportunity for estimating this characteristic number. Analyzing the 20 minute record of the original Draupner event recorded on New Year’s Day
1995, GPA indicates a characteristic number of waves exceeding 12, which is significantly larger than recorded in any previous analysis. This clearly indicates that GPA analysis of wave dynamics can be effectively exploited for a forecast of rogue wave prone storms. effects in optics first observed in the spatial domain have been demonstrated, including for example all-optical magnification of ultrafast data rates by a thousand fold, real-time detection of single-shot spectra at hundreds of MHz speed, or temporal cloaking. Here, exploiting duality between light propagation in space and time, we demonstrate the temporal analog of ghost imaging. We use a conventional fast detector that does not see the temporal ‘object’ to be characterized, and a slow integrating
‘bucket’ detector that does see the object but without resolving its temporal structure. Our experiments achieve temporal resolution at the picosecond level and show how temporal ghost imaging allows to overcome temporal distortions from a direct measurement induced by e.g. dispersion or attenuation. The approach is scalable, can be integrated on-chip and offers great promise for dynamic imaging of ultrafast waveforms.
9732-5, Session 1
Mathias Marconi, Philippe Hamel, Fabrice Raineri, Ariel
Levenson, Alejandro M . Giacomotti, Lab . de Photonique et de Nanostructures (France)
9732-7, Session 1
Brett H . Hokr, Texas A&M Univ . (United States); Marlan
O . Scully, Texas A&M Univ . (United States) and Baylor
Univ . (United States) and Princeton Univ . (United States);
Vladislav V . Yakovlev, Texas A&M Univ . (United States)
Intense research is currently devoted to extreme events –such as rogue waves– in photonic devices such as supercontinuum optical fibers [1], mode-locked lasers and more recently integrated photonic resonators [2].
In general, high pumping levels (either for passive or active devices) are required in order to reach heavy tail statistics in the output intensity.
In this work we show that extreme event statistics can emerge from nonlinear semiconductor coupled cavities with energy levels as low as few hundreds of emitted photons. For this, we use a nanophotonic device given by two coupled semiconductor photonic crystal nanolasers. This system has been recently shown to undergo spontaneous breaking of the mirrorsymmetry through a pitchfork bifurcation of the stable lasing (antibonding) state of the compound cavity system [3].
Here we study the intensity fluctuations of the second, unstable (bonding) mode. We observe heavy tail statistics in the form of deviations from exponential (Rayleigh) distributions. We show that the emission of this dark mode exhibits large fluctuations with mean output energies of only few hundreds of emitted photons. This opens a new avenue for the study of large deviations in the statistics of “few photon” states.
[1] Dudley et al., Nature Photonics, 8(10), 755-764 (2004)
[2] Liu et al, Nature Physics 11, 358–363 (2015)
[3] Ph. Hamel et al., Nature Photonics 9, 311 (2015)
Wide-field microscopy, where full images are obtained simultaneously, is limited by the power available from speckle-free light sources. Currently, the vast majority of wide-field microscopes use either mercury arc lamps, or LED’s as the illumination source. The power available from these sources limits wide-field fluorescent microscopy to tens of microseconds temporal resolution. Lasers, while capable of producing high power and short pulses, have high spatial coherence. This leads to the formation of laser speckle that makes such sources unsuitable for wide-field imaging applications.
Random Raman lasers offer the best of both worlds by producing laserlike intensities, short, nanosecond-scale, pulses, and low spatial coherence, speckle-free, output. These qualities combine to make random Raman lasers
4 orders of magnitude brighter than traditional wide-field microscopy light sources. Furthermore, the unique properties of random Raman lasers make possible the entirely new possibilities of wide-field fluorescence lifetime imaging or wide-field Raman microscopy. We will introduce the relevant physics that give rise to the unique properties of random Raman lasing, and demonstrate early proof of principle results demonstrating random Raman lasing emission being used as an imaging light source. Finally, we will discuss future directions and elucidate the benefits of using random Raman lasers as a wide-field microscopy light source.
9732-6, Session 1
Piotr Ryczkowski, Margaux Barbier, Tampere Univ . of
Technology (Finland); Ari Friberg, Univ . of Eastern Finland
(Finland); John M . Dudley, Univ . de Franche-Comté
(France); Goëry Genty, Tampere Univ . of Technology
(Finland)
Ghost imaging is a technique for constructing an image of an object without actually seeing this object. It is based on structured illumination where the correlation between light transmitted through an object and the spatiallyresolved intensity pattern of the incident light allows to reconstruct a ghost image of the original object. A central aspect to ghost imaging is the mutual spatial correlation of the two beams, which may be quantum or classical.
Various light sources can be used including spatially-entangled photon sources, spatially incoherent classical light sources, or structured light fields programmed by a spatial light modulator.
Exploiting space-time duality, the temporal analog of many propagation
9732-8, Session 2
(Invited Paper)
Tsz Chun Wong, Michelle Rhodes, Rick Trebino, Georgia
Institute of Technology (United States)
The challenges facing single-shot measurement of supercontinuum are many. Typical supercontinuum generated from photonic-crystal fiber is several ps long and has well over 100 nm of spectral bandwidth, easily achieving a time-bandwidth product (TBP) of ~100 or more. As a result, such supercontinuum pulses are extremely complex, with fine structure in both the temporal and the spectral domains. To further complicate the task, due to the small cores of photonic-crystal fiber, a supercontinuum pulse is quite weak, having at most ~20 nJ of energy. Since this energy is spread over a few ps, the intensity of these pulses is also quite low. While addressing one (or occasionally two) of these requirements at a time is now routine, addressing them all simultaneously in order to measure supercontinuum on a single shot has not yet been accomplished, despite an ever-increasing need to do so.
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Conference 9732: Real-time Measurements,
Rogue Events, and Emerging Applications
Here, we report a general technique that succeeds in this endeavor. In order to deal with the low energy of the supercontinuum pulse, we use a cross-correlation frequency resolved optical gating (XFROG) setup with a high-energy (regeneratively amplified) reference pulse. This setup provides much more signal and hence sensitivity than a self-referenced nonlinear measurement. Even better, XFROG has been demonstrated to retrieve extremely complicated pulse shapes very reliably[29]. We crossed the pulses at an angle, mapping relative delay onto transverse position, using the so-called transverse geometrical smearing in order to achieve single-shot measurement (and which also avoids any distortions due to the smearing effect). We also chose a polarization-gating (PG) geometry, which has essentially infinite bandwidth and so nicely solves the spectral-width problem immediately. Unfortunately, PG is a third-order nonlinear process and therefore, even with a high-intensity reference pulse, still requires a relatively long (>1mm) nonlinear medium for adequate signal strength.
This ordinarily proves highly problematic due to so-called longitudinal geometrical smearing effects. We solved this problem by imparting significant pulse-front tilt onto the reference pulse and simultaneously using a particular beam-crossing angle that precisely cancels out the geometrical smearing. This conveniently also increased the delay range, increasing the maximum measurable pulse length.
With this technique, we were able to measure complex supercontinua on a single shot for the first time. We will discuss this technique and these measurements, as well as other issues important to measuring such pulses.
9732-9, Session 2
Mohammad H . Asghari, Univ . of California, Los Angeles
(United States); Paul Trinh, Time Photonics Inc . (United
States); Bahram Jalali, Univ . of California, Los Angeles
(United States)
9732-10, Session 2
Piotr Antonik, Michiel Hermans, François Duport, Marc
Hälterman, Serge Massar, Univ . Libre de Bruxelles
(Belgium)
Reservoir Computing is a bio-inspired computing paradigm for processing time dependent signals that is particularly well suited for analog implementations. Our team has demonstrated several photonic reservoir computer with performance comparable to digital algorithms on a series of benchmark tasks such as channel equalisation and speech recognition.
Recently, we showed that our opto-electronic reservoir computer could be trained online with a simple gradient descent algorithm programmed on an FPGA chip. This setup makes it in principle possible to feed the output signal back into the reservoir, and thus highly enrich the dynamics of the system. This will allow to tackle in hardware complex prediction tasks, such as pattern generation, chaotic and financial series prediction, that have so far only been studied in digital implementations. Here we report simulation results of our opto-electronic setup with FPGA chip and output feedback applied to pattern generation and Mackey-Glass chaotic series prediction.
The simulations take into account the major aspects of our experimental setup. We find that pattern generation can be easily implemented on the current setup with very good results. The Mackey-Glass series prediction task is more complex and requires a large reservoir and more elaborate training algorithm. With these adjustments promising result are obtained, and we now know what improvements are needed to match previously reported numerical results. These simulation results will serve as basis of comparison for experiments we will carry out in the coming months.
9732-11, Session 2
Yiqing Xu, Xiaoming Wei, Zhibo Ren, Kenneth K . Y . Wong,
Kevin Tsia, The Univ . of Hong Kong (Hong Kong, China)
The real-time measurement of fast non-repetitive events is arguably the most challenging problem in the field of instrumentation and measurement.
These instruments are needed for investigating rapid transient phenomena such as chemical reactions, fast physical phenomena, phase transitions, protein dynamics in living cells and impairments in data networks. Optical spectrometers are the basic instrument for performing sensing and detection in chemistry, physics and biology applications. Unfortunately, the scan rate of a spectrometer is often too long compared with the timescale of the physical processes of interest. In terms of conventional optical spectroscopy, this temporal mismatch means that the instrument is too slow to perform real-time single-shot spectroscopic measurements. Single-shot measurement tools such as frequency-resolved optical gating (FROG) and spectral phase interferometry for direct electric-field reconstruction
(SPIDER) are, although powerful, therefore unable to perform pulseresolved spectral measurements in real time.
Roguescope is a commercially available single-shot optical spectrometer with a frame rate of up to 100 Million frames per second, at least one thousand times faster than the next fastest spectrometer. The Roguescope real-time capability is enabled by photonic time-stretch implemented by
Time-Stretch Dispersive Fourier Transform. The Roguescope can capture large data sets to reveal rare events with meaningful accuracy. Applications include optical rouge waves, laser transients, chemical reactions, and nonlinear dynamics. RogueScope is an essential tool for measurements of fast stochastic processes such as laser transients, rare events and outliers in optical systems. RogueScope is ideal for capturing non-Gaussian statistics that are signatures of complex dynamics.
Nonlinearly generated broadband ultrafast laser have been increasingly utilized in many applications. However, traditional techniques of characterizing these sources lack the ability to observe the instantaneous features and transitory behaviours of both amplitude and phase. With the advent of the optical time stretch techniques, the instantaneous shotto-shot spectral intensity can be directly measured continuously at an unprecedentedly high speed. Meanwhile, the information of the real-time phase variation, which is carried by the frequency-time mapped spectral signal has yet been fully explored.
We present a technique of experimentally measuring the spectral coherence dynamics of broadband pulsed sources. Our method relies on a delayed
Young’s type interferometer combined with optical time-stretch. We perform the proof-of-principle demonstrations of spectral coherence dynamic measurement on two sources: a supercontinuum source and a fiber ring buffered cavity source, both with a repetition rate of MHz. By employing the optical time stretch with a dispersive fiber, we directly map the spectral interference fringes of the delayed neighbouring pulses and obtain a sufficiently large ensemble of spectral interferograms with a real-time oscilloscope (80Gb/s sampling rate). This enables us to directly quantify the spectral coherence dynamics of the ultrafast sources with a temporal resolution down to microseconds. Having the ensemble of singleshot interferograms, we also further calculate the cross spectral coherence correlation matrices of these ultrafast sources. We anticipate that our technique provides a general approach for experimentally evaluating the spectral coherence dynamics of ultrafast laser generated by the nonlinear processes e.g., modulation instability, supercontinuum generation, and Kerr resonator.
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9732-12, Session 2
Sylvain Barbay, Félix Lelièvre, Ali Golestani, Foued Selmi,
Rémy Braive, Grégoire Beaudoin, Isabelle Sagnes, Lab . de
Photonique et de Nanostructures (France)
A micropillar laser with integrated saturable absorber and delayed feedback is shown experimentally and theoretically to sustain controllable trains of dissipative temporal solitons controlled by adequate optical perturbations in the excitable regime. We show that the pulse train can be started or resynchronized (retiming) with a single perturbation and that the system can store a large variety of temporal pulse patterns. We discuss the relevance of the various timescales at stake for such functionalities.
Besides its interest as a compact source of controllable pulses that can be arranged if needed in arrays, this system has also interesting potential for neuromimetic processing of information since it can be considered as a leaky-integrate-and-fire (LIF) optical neuron with delayed feedback.
The LIF neuron model is a widespread model in neuroscience and in neurocomputing models and as such it is at the foundation of neural networks, a promising avenue for alternative computation systems.
9732-13, Session 3
Conference 9732: Real-time Measurements,
Rogue Events, and Emerging Applications
(Invited
Paper)
Majid Taki, Zheng Liu, Saliya Coulibaly, Univ . des Sciences et Technologies de Lille (France); François Léo, Univ . Libre de Bruxelles (Belgium)
9732-14, Session 3
Svetlana Slepneva, Tyndall National Institute (Ireland);
Ben O’Shaughnessy, Cork Institute of Technology (Ireland) and Tydall National Institute (Ireland); Stephen P . Hegarty,
Cork Institute of Technology (Ireland) and Tyndall
National Institute (Ireland); Bryan Kelleher, Univ . College
Cork (Ireland); Sergio Rica, Univ . Adolfo Ibáñez (Chile);
Guillaume Huyet, Cork Institute of Technology (Ireland) and Tyndall National Institute (Ireland)
We investigate both theoretically and experimentally the properties of a 20km long unidirectional fiber ring cavity laser that includes a semiconductor optical amplifier and a tunable Fabry-Perot filter. The laser displays turbulent dynamics when the filter transmission is set at a wavelength longer than 1320nm since the laser operates in a self-focusing regime. At lower wavelengths the laser displays multistability between cw and turbulent regimes. We investigate the stability of these solutions both numerically and experimentally by controlling the value of detuning, which is the frequency mismatch between the filter driving frequency and the cavity roundtrip frequency. For the decreasing detuning, the cw solution becomes unstable leading to the appearance of turbulent emission.
For the increasing detuning, a subcritical bifurcation occurs, leading to the stabilisation of another cw solution via a turbulent regime. To further investigate the dynamics of this regime, we drive the filter in resonance with the laser round trip frequency. This regime, referred to as Fourier Domain
Mode-Locking (FDML), is commonly used to design high-frequency swept sources since the entire sweep is stored in the cavity. It is also worthwhile to notice the analogy with a one dimensional system with a spatiallyvarying detuning. In such a case, we observe the formation of cw and turbulent domains and near the subcritical bifurcation point, we observe the continuous formation of convective turbulent domains that grow and merge into one turbulent region. A detailed analysis shows that these domains emerge from the cw solution by first creating Nozaki-Bekki holes.
We study analytically, numerically and experimentally the spontaneous formation of dissipative periodic solutions in a coherently driven passive optical fiber cavity under Raman effect and third-order dispersion. It is shown that the latter, that breaks the time-reversal symmetry, affects the bifurcation nature, at onset of the instability, leading to a transition from a sub- to a super-critical bifurcation. The analytical description of this bifurcation demonstrates an original dependence of the nonlinear saturation term upon the third-order dispersion. A striking feature is the existence of an optimal nonlinear resonance leading the maximum asymmetry in the spectrum. Our theory reveals the key role of third-order dispersion on the asymmetry in the spectrum of the dissipative structures, explains early observations, and the predictions are in excellent agreement with our experimental findings.
In the strongly nonlinear regime, Eckhaus instabilities characterize the secondary instabilities where stable propagating dissipative wave-trains are generated with a definite frequency and a constant group velocity. Their stability range is enlarged in the presence of the third-order dispersion, which determines completely their group velocity.
An increasing in the injected pump value leads to transitions from periodic wave trains to chaotic regimes with a continuous spectrum and the appearance of rogue waves in the form of abnormal high amplitudes. We have analytically characterized this transition and determined the transition curves from regular to chaotic regimes where supercontinuum and rogue waves may occur.
9732-15, Session 3
Ravitej Uppu, Tata Institute of Fundamental Research
(India) and Univ . Twente (Netherlands); Sushil A .
Mujumdar, Tata Institute of Fundamental Research (India)
Random lasers are intriguing complex systems that have proven to be a rich testbed of unique statistical studies. Based on the interplay of optical gain and light diffusion [1], the inherent randomness in these systems manifests several fluctuations, including the realization of non-Gaussian heavy-tailed intensity distributions. One puzzling phenomenon observed from these apparently ‘dirty’ systems is the genesis of first-order temporally coherent peaks in the emission spectrum. The high intensities of these peaks constitute the outliers in an otherwise well-behaved distribution. The origin of coherent emission in these systems has recently been modeled using a novel platform of exponentially tempered Lévy sums [2]. The underlying
Lévy variables correspond to the amplified spontaneous emission photons that diffuse through multiple scattering.
The exponentially-tempered Levy sum model was shown to accurately capture the strong intensity fluctuations. These strong fluctuations in the sums signify strong fluctuations of the extreme values in the summands, i.e. the Lévy variables. Here, we explore the importance of these rare extreme summands in determining the fluctuations in the Lévy sums. Further, we investigate the effect of tempering on the rarity of these extreme summands to explain the Lévy to Gaussian crossover in the statistics of sums. Careful experimental analysis along with detailed photon transport
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Conference 9732: Real-time Measurements,
Rogue Events, and Emerging Applications
Monte Carlo simulations signify the importance of rare extreme summands in determining the statistical nature of the intensity fluctuations in random laser emission.
[1] D.S. Wiersma, Nat. Phys., 4, 359 (2008)
[2] R. Uppu, and S. Mujumdar, Phys. Rev. Lett., 114, 183903 (2015)
Finally, we will discuss how the spectral dynamics, i.e. instantaneous spectrum at each cavity round-trip, could be measured in fiber lasers generating irregular train of pulses of quasi-CW radiaton via combination of heterodyning and intensity spatio-temporal measurement concept. Using this method, we will reveal the existence quasi-stationary localizes lasing modes in the radiation of random fibre laser.
9732-16, Session 3
Sylvain Barbay, Lab . de Photonique et de Nanostructures
(France); Saliya Coulibaly, Lab . de Physique des Lasers,
Atomes et Molécules (France); Foued Selmi, Lab . de
Photonique et de Nanostructures (France); Marcel G . Clerc,
Univ . de Chile (Chile)
Extreme and rare events are ubiquitous in nature. They are characterized by rare and high amplitude excursions of a given variable characterizing a physical system with respect to its long time average. The study of extreme events and extreme waves in optics has been primarily motivated by the analogy with rogue waves in hydrodynamics whose formation mechanism is still not well understood but include ingredients such as spatial instabilities, nonlinearities and noise. Here we consider a spatially extended microcavity laser with integrated saturable absorber in the self-pulsing regime. This system has two advantages: first, its typical timescales are fast enough to allow large recordings in a small amount of time and hence to allow for accurate statistics. Second and even more important, it does not display irregular or aperiodic dynamics and hence extreme events without spatial coupling. Hence we can really study the role of spatial coupling in the emergence of extreme events. By recording the dynamics simultaneously in two different spatial points we are able to study whether the extreme events occur through a mechanism of coherent structure collision, as already reported in different systems. With the help of a mathematical model, linear stability and numerical analysis of the dynamics we unveil the dynamical origin of the extreme events found in the occurrence of spatiotremporal chaos rather than in the merging dynamics of coherent structures. The understanding of the formation mechanism of these extreme phenomena is an important step to devise strategies to control them.
9732-17, Session 4
(Invited
Paper)
Dmitry V . Churkin, Aston Univ . (United Kingdom); Srikanth
Sugavanam, Aston University (United Kingdom)
Usually lasers are thought to be operated in some temporal regime. In our work we experimentally show that a laser could be operated in a distinct, albeit complex and dynamic spatio-temporal regime. Different spatio-temporal regimes could have different periodicity properties over different scales, i.e. different spatio-temporal patterns could emerge. We will demonstrate the methodology of real-time measurements of intensity spatio-temporal dynamics on an example of passively mode-locked fibre laser generating noise-like pulses of stochastic filling. Different spatiotemporal generation regimes varying by their stochasticity and periodicity properties are experimentally found.
Further, we propose an experimental tool of ACF evolution mapping to reveal the constituents of thought-to-be stochastic radiation and will use this tool to directly detect various types of dark and bright localised structures, including spatio-temporal rogue waves and shock waves, generating within though-to-be stochastic temporal dynamics.
9732-18, Session 4
Amaury Mathis, Pierre-Ambroise Lacourt, Luc Froehly,
Shanti Toenger, FEMTO-ST (France); Frédéric Dias, Univ .
College Dublin (Ireland); Goery Genty, Tampere Univ . of
Technology (Finland); John M . Dudley, FEMTO-ST (France)
Rogue waves are statistically rare events with extreme amplitude or intensity which have been observed in numerous physical systems. In optics particularly, the study of rogue waves has provided new insights into the dynamics of noise-induced soliton propagation during supercontinuum generation. Most studies have focused on how nonlinearity can lead to rogue-wave behavior, but we report here an experimental demonstration of optical rogue waves in a purely linear system which yields a 2D random spatial “sea” of coherent radiation. The experiments are based on free space propagation of a random spatial phase applied via spatial light modulator.
By varying the nature of the applied random phase pattern, we are able to see the development of random caustics in the propagating field that yield large amplitude events that satisfy the “significant wave height” criteria of rogue waves. To validate this analogy, we performed optical phase retrieval techniques on the propagating field to extract the amplitude from the intensity distribution – amplitude, not intensity, being relevant in an oceanic context. Additional results show the clear relationship between the width of the spatial spectrum and the emergence of rogue wave events. Indeed, slightly non-Gaussian spectra with high-frequency content but no strong focusing were tested, significantly modifying the statistics of events. These results from optics confirm previous studies of the possible role of caustics in ocean wave dynamics, and provide further evidence that purely linear mechanisms cannot be discounted when studying rogue wave generation mechanisms.
9732-19, Session 4
Sergey V . Sergeyev, Chengbo Mou, Stanislav Kolpakov,
Vladimir Kalashnikov, Sergei K . Turitsyn, Aston Univ .
(United Kingdom)
Rogue wave (RWs) as a concept has been initially introduced in oceanography to describe giant waves with amplitudes that are much larger than an average and so, despite low emergence probability, resulting in destructive impact in nature and society. The main obstacles in modelling and predicting RWs is in the scarcity of events and inability to perform fullscale experiments to cause rogue waves to appear in real-world scenarios such as financial markets, power grids, oceans, human brains etc. In this context, mode-locked lasers are perfect test bed systems to study RWs origin and techniques of mitigation with a potential to apply results in numerous disciplines – social sciences, natural sciences and technology and engineering. Here for the first time we demonstrate experimentally and theoretically a new mechanism of deterministic vector RWs emergence in erbium-doped fiber lasers mode-locked with carbon nanotubes. Unlike fast RW dynamics in lasers with pulse-to-pulse power variation, we have found slow vector rogue waves which have the states of polarization and power variations at the time scale of hundreds round trips. We showed that tuning the birefringence and anisotropy in cavity enables random switching between two orthogonal states of polarization that is similar to the stimulated by periodic barrier modulation transitions of the Brownian particle between two potential wells, i.e. Stochastic Resonance. Tailoring
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Conference 9732: Real-time Measurements,
Rogue Events, and Emerging Applications anisotropy in the cavity leads to asymmetry in the escape probabilities from the potential wells that under certain conditions results in rare switching events with the output power distribution satisfying criteria of RWs.
9732-20, Session 4
Moti Fridman, Shir Shahal, Vlada Artel, Doron Naveh, Bar-
Ilan Univ . (Israel) integrable turbulence.
Numerical simulations of 1D-NLSE with stochastic initial conditions reproduce quantitatively the experiments. Our numerical investigations suggest that the statistical features experimentally observed rely on the stochastic generation of coherent analytic solutions of 1D-NLSE.
Pierre Walczak, Stéphane Randoux, and Pierre Suret, Optical Rogue Waves in Integrable Turbulence, Phys. Rev. Lett. 114, 143903 (2015)
9732-22, Session 4
Saliya Coulibaly, Zheng Liu, Majid Taki, Univ . des Sciences et Technologies de Lille (France)
Optical isolators which serve as one-way optical channels are a crucial component in numerous applications [1]. To obtain optical isolation, the time reversal symmetry must be broken. This braking of time reversal symmetry is usually done via Faraday rotator with constant magnetic field [2] and was also demonstrated with nonlinear interaction of traveling pump waves [3] and with circular polarized light manipulations [4].
We present, optical isolator based on the interaction between light and topological isolators. Our optical isolator is free from external magnetic field and is based on spontaneous time reversal symmetry braking by the topological insulators. The time reversal symmetry braking is obtained through the interaction of the traveling light in tapered fiber with the topological electrons in the surface and in the bulk of Sb2Te3 nano-particles.
The interaction of light with the topological electrons rotates the input polarization similar to the Faraday rotator but with no external magnetic field.
Our technique can lead to novel type of non-reciprocal fiber devices and can be implemented in on-chip photonic waveguides. The full experimental and theoretical details of our optical isolator will be presented.
References:
[1] D. Jalas, et. al. “What is – and what is not – an optical isolator” Nat.
Photon. 7, 579 (2013)
[2] K. Shiraishi, et. al., Appl. Opt. 23, 1103 (1984)
[3] H. Ramezani, et. al. Phys. Rev. A 82, 043803 (2010)
[4] J. W. Goodman “Introduction to Fourier optics” (2005)
The frequency combs have emerged as a powerful tool for high-resolution metrology. If in the beginning, ultrafast mode-locked lasers were the main sources of frequency combs, there are now new ways to generate them. By new ways, we especially refer to those based on the use of continuously pumped optical cavity containing a Kerr-type medium–Kerr frequency comb. That is, the Kerr frequency combs belong to the category of optical dissipative structures since they correspond to the spectra associated to the cavity solitons or the periodic solutions and so far, expected to exhibit complex dynamics. In this study, we focused on the dynamics of the periodic solutions that appear in Kerr cavities. More specifically, we study the route to the chaos that flows out from these structures. What we propose here is to consider the route to chaos by means of dynamical systems theory and chaos tools in extended systems. For this purpose, we consider the Lugiato-Lefever model which describes the dynamics of intra-cavity field in Kerr cavities. An instability of the basic solution of this model gives rise to a tunable periodic state with a comb-like spectrum. After providing an analytical description of this comb, its stability analysis have been carried out by means of computation the Lyapunov spectrum allowing to characterize the transition from stable comb to chaotic regime in which rogue waves have been observe and statistically characterized.
9732-21, Session 4
Pierre Suret, Lab . de Physique des Lasers, Atomes et
Molécules (France); Pierre Walczak, Stephane Randoux,
Univ . des Sciences et Technologies de Lille (France) and Lab . de Physique des Lasers, Atomes et Molécules
(France)
9732-23, Session 5
(Invited Paper)
Wolfgang Draxinger, Wolfgang Wieser, Optores GmbH
(Germany); Jan Philip Kolb, Tom Pfeiffer, Matthias Eibl,
Univ . zu Lübeck (Germany); Thomas Klein, Optores GmbH
(Germany); Sebastian N . Karpf, LMU München (Germany);
Robert A . Huber, Univ . zu Lübeck (Germany) and Ludwig-
Maximilians-Univ . München (Germany)
We report optical experiments allowing to investigate integrable turbulence in the focusing regime of the one dimensional nonlinear Schrodinger equation (1D-NLSE). In analogy with broad spectrum excitation of onedimensional water-tank, we launch random initial waves in a single mode optical fiber.
We have developed an original setup which allows the precise measurement of statistics of random light rapidly fluctuating with time. Inspired by the time-resolved fluorescence upconversion experiments and by the optical sampling (OS) oscilloscope, the principle of our method is based on asynchronous OS.
Using our apparatus, we measure precisely the probability density function
(PDF) of optical power of the partially coherent waves rapidly fluctuating with time. The typical time scale of the resolution is 250fs.
In the experiments performed in the focusing regime, the PDF of optical power fluctuations is found to evolve from the normal law to a strong heavy-tailed distribution, thus revealing the formation of rogue waves in
Fourier Domain Mode Locked (FDML) lasers are narrowband, rapidly wavelength swept light sources that can generate more than 100nm sweep range at 1000-1550nm center wavelength. At linewidths of a few pm, several million wavelength sweeps per second are possible. The main application of FDML lasers is optical coherence tomography (OCT), where they can achieve about 10x higher speed compared to most other approaches. OCT is a recent microscopic 3D imaging technique and FDML enables imaging speeds of several ten volumes per second. The corresponding voxel rate of about 2 Gigavoxel/s can be sustained and recently live processing of the data on a consumer grade graphics processing unit was demonstrated.
The live processing will be important for OCT applications like future OCT aided 4D surgical microscopes. Additionally, fast real-time OCT without live processing will have many more applications - especially in situations where patient motion, turbulent flow dynamics or a maximum total imaging time make non-realtime “sampling-type” approaches unacceptable. Besides the presentation of our own progress on evaluating emerging applications of ultra-high speed real-time OCT, the talk will review work and possibilities of
FDML lasers for fast real-time spectroscopy and sensing applications.
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Conference 9732: Real-time Measurements,
Rogue Events, and Emerging Applications
9732-24, Session 5
Christophe Dorrer, Leon Waxer, Adam Kalb, Elizabeth Hill,
Jake Bromage, Univ . of Rochester (United States) with transform limited spectra we can determine suitable initial coefficients and the fastest optimization method [1-4]. The algorithm takes advantage of MATLAB built-in tools for constrained and non-constrained optimization.
For complex synthetic pulses the algorithm converges in less than a minute with errors less than 0.1%. For measured pulses the error is limited by the uncertainty of nonlinear spectral measurements by different spectrometers which can be as large as 1%, therefore errors around or less than 1% for measured pulses are acceptable. Inclusion of third harmonic enables us to choose a better starting point and decreases the number of local minima which drastically reduces the convergence times and error. To eliminate time reversal ambiguity we can place a known material in the beam path and reduce the number of global minima to one.
Temporally characterizing optical pulses is an important task when building, optimizing, and using optical sources. Direct photodetection with highbandwidth photodiodes and real-time oscilloscopes is only adequate for optical pulses longer than ~10 ps; diagnostics based on indirect strategies are required to characterize femtosecond and sub-10-ps coherent sources.1
Most of these diagnostics are based on nonlinear optics and can be difficult to implement for the single-shot characterization of non-repetitive events.
A temporal diagnostic based on phase diversity has been demonstrated in the context of picosecond high-energy laser systems, where single-shot pulse measurements are required for system safety and interpretation of experimental results.2 A plurality of ancillary optical pulses obtained by adding known amounts of chromatic dispersion to the pulse under test are directly measured by photodetection and algorithms are used to accurately reconstruct the input pulse shape from the measured instantaneous power of the ancillary pulses versus time and optical spectrum. This high-sensitivity
(~30-pJ) diagnostic is based on a pulse replicator composed of fiber splitters and delay fibers, making it possible to operate with fiber sources and free-space sources after fiber coupling, and with pulses significantly shorter than the photodetection impulse response. Experimental data obtained with various oscilloscopes having bandwidth in the 45- to 70-
GHz range will be presented to demonstrate accurate operation at pulse durations in the 1- to 100- ps range. Simulations of the diagnostic and pulsereconstruction algorithm will be presented.
This material is based upon work supported by the Department of Energy
National Nuclear Security Administration under Award Number DE-
NA0001944, the University of Rochester, and the New York State Energy
Research and Development Authority. The support of DOE does not constitute an endorsement by DOE of the views expressed in this article.
1. Walmsley, I. A. and Dorrer, C., “Characterization of ultrashort electromagnetic pulses,” Adv. Opt. Photon. 1, 308–437 (2009).
2. Dorrer, C., Waxer, L., Kalb, A., Hill, E. M. and Bromage, J., “Single-shot characterization of optical pulses below the resolution limit by phasediversified photodetection,” [Conference on Lasers and Electro-Optics 2015],
OSA Technical Digest (online), Optical Society of America, Washington, DC,
Paper JTh5C.5 (2015).
9732-26, Session 5
Michelle Rhodes, Zhe Guang, Rick Trebino, Georgia
Institute of Technology (United States)
Multiple pulsing is a feature of most mode-locked ultrafast laser systems at very high pump powers, and slight variations in the pump power around certain regimes can cause sinusoidally-varying or even chaotic separations among pulses. While this behavior should be absent from well-engineered and well-aligned lasers, it is nevertheless still possible, especially if the system is poorly maintained. Although we have previously studied unstable trains of very noisy pulses, they are significantly different from simple satellite pulses. The impact of unstable multipulsing on modern pulse measurement methods is still unknown.
While spectral shearing interferometry for direct electric field reconstruction
(SPIDER) has been shown to be incapable of seeing fluctuating complex pulses, analytical models have suggested that small variations in separation between double-pulses could theoretically be visible in a SPIDER trace and in the resulting measured field, even if the relative phase of the two pulses is allowed to vary. However, we have now performed simulations and find that allowing only the relative phase of a satellite pulse to vary causes the satellite to wash out of the SPIDER measurement completely, even if the separation between pulses is stable. Allowing the separation between pulses
(or other pulse parameters) to vary also does not improve matters: SPIDER continues to measure only a single pulse, a phenomenon known as the coherent artifact.
On the other hand, although techniques like FROG and autocorrelation cannot accurately determine the precise properties of satellite pulses, they do succeed in seeing them.
9732-25, Session 5
Aram Gragossian, The Univ . of New Mexico (United
States); Brook A . Jilek, Sandia National Labs . (United
States); Mansoor Sheik-Bahae, The Univ . of New Mexico
(United States)
9732-27, Session 5
Sergey Smirnov, Sergey M . Kobtsev, Novosibirsk State
Univ . (Russian Federation)
There are many techniques for calculating the spectral phase of ultrashort pulses. They all use multiple expensive components and are difficult to build and expensive to buy. We present and algorithm for short pulse characterization buy using one spectrometer and three spectra. Spectral
Phase Interrogation using Nonlinear Spectra (SPINS) takes advantage of information embedded in fundamental, second harmonic (SH) and third harmonic (TH) spectra to retrieve the spectral phase and calculate pulse duration. SPINS generates trial SH and TH from the measured fundamental and an initial guess for the spectral phase. The spectral phase is approximated by 6th order Taylor expansion around central frequency.
These coefficients are adjusted until the difference between measured and trial SH and TH is minimized. By comparing measured nonlinear spectra
Noise-like pulses (NLP) generated in certain passively mode-locked regimes of fibre lasers [1] hold a substantial promise in various applications because they can carry relatively high energy, are not sensitive to the propagation medium dispersion, and can be non-linearly transformed with comparatively high efficiency [2, 3]. However, the structure of these pulses is still not completely understood, and neither is the statistics of temporal&spectral
NLP components. The present paper for the first time proposes and studies a relatively simple NLP model that matches the experimental data well and suggests that there is a correlation between phases of neighbouring spectral components of NLP. Comparison of a relatively basic model of “random pulses” with the results of NLP modelling in mode-locked fibre lasers based on coupled non-linear Schrödinger equations (NLSE) demonstrates that
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Conference 9732: Real-time Measurements,
Rogue Events, and Emerging Applications it is possible to use this proposed model for highly efficient simulations of promising NLP applications, such as material processing, non-linear frequency conversion, microscopy, and others. The present work explains the proposed NLP model and compares temporal distributions, intensity autocorrelation function of NLP, statistics of sub-pulse duration, and figures of mode cross-correlations predicted by new model and by NLSE. Further discussed is the possible application of the proposed model in studies of transitional lasing regimes (intermediate between generation of coherent pulses and NLP).
1. S. Smirnov, et al. Optics Express 20(24), 27447 (2012).
2. S. Smirnov, et al. Optics Express 22(1), 1058 (2014).
3. S. Kobtsev, et al. Optics Express 22(17), 20770 (2014).
9732-28, Session 5
Chien-Fang Ding, Meng-Shiou Lee, Kuan-Ming Li, National
Taiwan Univ . (Taiwan)
Since their invention, lasers have been applied in many fields, including material processing, communications, metrology biomedical engineering, and defense. Laser power is an important parameter in laser material processing, for example, laser cutting and laser drilling. Because laser power is influenced by ambient temperature, laser power status is monitored using laser power meters to ensure effective material processing. Current laser power meters have long response times. Consequently, they cannot measure laser power accurately within a short time. To achieve simultaneous laser power monitoring and effective material processing, we developed a complementary metal-oxide-semiconductor (CMOS) camera–based online laser power monitoring system. The CMOS camera captures images of an incident laser beam after it is split and attenuated by a beam splitter and a neutral density filter, respectively. By comparing the average brightness of the beam spots and the measurement results of the laser power meter, we can estimate laser power. In the continuous measurement mode, the average measurement error of the developed laser power monitoring system was approximately 3%, and it responded at least 3.6 s quicker than conventional thermopile power meters do. In the trigger measurement mode, which allows for synchronization of the CMOS camera with intermittent laser output, the average measurement error was lower than
3%, and the quickest response time was 20 ms.
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9733-1, Session 1
Dennis Bonsendorf, Stephan Schneider, Jens Meinschien,
LIMO Lissotschenko Mikrooptik GmbH (Germany); Jens
W Tomm, Max-Born-Institut für Nichtlineare Optik und
Kurzzeitspektroskopie (Germany)
Direct diode laser systems gain importance in the fields of material processing and solid-state laser pumping. With increased output power, also the influence of strong optical feedback has to be considered. Uncontrolled optical feedback is known for its spectral and power fluctuation effects, as well as potential emitter damage. We found that even intended feedback by use of volume Bragg gratings (VBG) for spectral stabilization may result in emitter lifetime reduction. To provide stable and reliable laser systems design, guidelines and maximum feedback ratings have to be found. We present a model to estimate the optical feedback power coupled back into the laser diode waveguide. It includes several origins of optical feedback and wide range of optical elements. The failure threshold of InGaAs and
AlGaAs bars has been determined not only at standard operation mode but at various working points. The influence of several feedback levels to laser diode lifetime is investigated up to 4000h. The analysis of the semiconductor leads to a better understanding of the degradation process by defect spread. Facet microscopy, LBIC- and electroluminescence measurements deliver detailed information about semiconductor defects before and after aging tests. Laser diode protection systems can monitor optical feedback. With this improved understanding, the emergency shutdown threshold can be set low enough to ensure laser diode reliability and high enough to provide better machine usability avoiding false alarms.
9733-2, Session 1
Jens Wolfgang W . Tomm, Martin Hempel, Max-Born-
Institut für Nichtlineare Optik und Kurzzeitspektroskopie
(Germany); David Venables, Victor Rossin, Erik Zucker,
Lumentum (United States); Thomas Elsaesser, Max-Born-
Institut für Nichtlineare Optik und Kurzzeitspektroskopie
(Germany)
Single-spatial mode lasers emitting at 980-nm are exposed to two types of lifetime testing, namely rapid stress-testing and long-term aging. We find that both activate the same sudden degradation mechanism, namely internal catastrophic optical damage at 0.6-1.0 mm behind the front facet.
In the case of ultra-high power operation, we show that the mechanism that initializes this effect is a lateral widening of the optical mode, resulting in increased absorption outside the waveguide. Defects formed during longterm aging may eventually lead to a comparable mode distortion and finally to device failure. Single-pulse stress-testing allows for activation several degradation mechanisms in a device one after the other, and allows for distinguishing between gradual aging and defects that are independent of the aging status.
Although the results presented are monitored with a rather complex setup, it turns out that monitoring the devices along their laser-axis with cameras provides rich information on gradual and sudden degradation effects. We expect that after once the acting mechanisms are understood, stress-tests can be performed with simple and cheap setups, consisting of a pulse generator and a standard CCD-camera only. Although we are convinced that accelerated long-term aging tests will remain the main method for lifetime predictions of diode lasers, stress-tests could pave the way towards more time-efficient testing, e.g., for comparison of different technology variants in development. While this report focuses on the behavior of a specific device type, both setup and methodology are transferable to other types of diode lasers.
9733-3, Session 1
Yongkun Sin, Nathan Presser, Zachary Lingley, Miles
Brodie, Adam Bushmaker, Brendan Foran, Steven C . Moss,
The Aerospace Corp . (United States)
High-power single- and multi-mode InGaAs-AlGaAs strained QW lasers are critical components for telecommunications and potential space satellite communications systems. However, little has been reported on failure modes of state-of-the-art SM InGaAs-AlGaAs strained QW lasers although it is crucial to understand failure modes and underlying degradation mechanisms in developing these lasers that meet lifetime requirements for space satellite systems. Our present study addresses these issues by performing long-term life-tests followed by FMA and physics-of-failure investigation.
We performed long-term accelerated life-tests on state-of-the-art SM and
MM InGaAs-AlGaAs strained QW lasers. Our life-tests have accumulated over 20,000 test hours for SM lasers and over 35,000 test hours for MM lasers. FMA was performed on failed SM lasers using EBIC. This technique allowed us to identify failure types by observing dark line defects. All the
SM failures we studied showed catastrophic and sudden degradation and all of these failures were bulk failures. Our group previously reported that bulk failure or COBD is the dominant failure mode of MM InGaAs-AlGaAs strained
QW lasers and this is the first report demonstrating that the dominant failure mode of SM and MM InGaAs-AlGaAs strained QW lasers is the bulk failure. Since degradation mechanisms responsible for COBD are still not well understood, we also employed FIB and high-resolution TEM to further study dark line defects and dislocations in pre- and post-aged SM and MM lasers. In addition, the photocurrent spectra were measured from localized areas to study the effects of COBD on changes in absorption characteristics in MM lasers.
9733-4, Session 1
Tetsuya Yagi, Kyosuke Kuramoto, Kaoru Kadoiwa, Ryuta
Wakamatsu, Motoharu Miyashita, Mitsubishi Electric Corp .
(Japan)
The digital cinema projector based on laser light source started its installation to the theaters, and the laser diode (LD) backlight LCD already appeared in the consumer market. So far, the next may be a laser based projector with one spatial light modulator (SLM), which uses the laser light source under the pulse condition for time division color expression. We already developed the 638 nm triple emitter broad area (BA) LD assembled
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Conference 9733: High-Power Diode Laser
Technology and Applications XIV on 9.0-mm TO package for this application, which outputs peak power of 5.5 W under pulse operation with duty cycle (Dc) of 30%, 25 C. In this paper, the latest reliability study on this LD will be described in detail. Main cause of the degradation of 638-nm BA-LD is catastrophic optical mirror degradation (COMD). It was reported that the output power, at which the
COMD occurs, (Pcod) decreases as the aging time goes by. When Pcod reaches to the operation power, the failure due to COMD occurs. The Pcod behaviors on the several aging conditions were studied. It was revealed that the mean time to failure (MTTF) of the LD was proportional to the
-4.3 power of the output power. The long term aging under the over-drive condition was also performed. The emitter failed individually and the failed emitter didn’t affect the other emitters in the same chip. By using them, the
MTTF of this LD was estimated exceeding 20,000 hours under the output of
2.5 W, Dc of 30%.
levels over 15 W and 20 % conversion efficiency from 20% FF bars with 2 mm cavity length on a conductively cooled platform. Life testing of the 1470 nm lasers bars over 14,000 hours under constant current mode has shown no significant degradation.
9733-7, Session 2
David A . Schleuning, Athanasios N . Chryssis, Geunmin Ryu,
Guoli Liu, Heiko Winhold, Li Fan, Zuntu Xu, Tawee Tanbun-
Ek, Sami Lehkonen, Bruno Acklin, Coherent, Inc . (United
States)
9733-5, Session 1
Jorge Souto, Jose Luis Pura, Alfredo Torres, Juan Jimenéz,
Univ . de Valladolid (Spain); Mauro A . Bettiati, Francois J .
Laruelle, 3SP Technologies S .A .S . (France)
Many direct diode and fiber laser pumping applications require a multi-kW laser diode module. A new 9xx nm laser diode chip has been developed with improved efficiency, brightness, and reliability. A water-cooled packaging architecture utilizing hard solder has been developed using an electrically isolated cooler which provides low thermal resistance (<0.25 oK/W). The package has been studied in accelerated CW conditions as well as hard-pulse on-off cycling mode operation. The electrical isolation enables the use of “tap water” to cool the laser diodes. A fiber-coupled module converts the asymmetric fast and slow axis beams into an optical fiber with over 2kW of power in a single wavelength, single polarization configuration.
The module has passed a number of passive environmental qualification tests. Extensive accelerated multi-cell lifetests using packaged bars, water cooled stacks, and optical modules have been performed with over ten million device hours of test.
The catastrophic optical degradation (COD) of high power laser diodes is described on the bases of the cathodoluminescence (CL) analysis of the degraded areas, and a thermomechanical model accounting for the mechanism leading the degradation process. The COD is frequently observed at the front mirror; although, under very high power conditions
(pulsed current operation) internal COD can also occur. CL is a very suitable experimental technique to reveal the main features of degradation in laser diodes; the defects generated by the degradation in the laser cavity are observed by CL imaging; simultaneously spectrally resolved CL permits to monitor the spectral changes induced by the degradation. The COD is observed as a very local process, associated with the formation of networks of extended defects and subsequent propagation as a result of the local enhancement of the temperature. In view of this observation, one can set-up a thermomechanical model describing the thermal runaway leading to the
COD. The thermal stresses generated by the local heating are the leading forces driving the plastic deformation of the laser structure; the generation and propagation of networks of dislocations, mostly localized in the QW layer, are observed in the CL images. Important physical parameters of the laser structure involved in this process are the thermal conductivity and the mechanical strength. We demonstrate that the evolution of these parameters during laser operation accounts for the sudden temperature increase in local regions of the laser cavity.
9733-6, Session 1
Tawee Tanbun-Ek, Rajiv Pathak, Zuntu Xu, Heiko Winhold,
Serguei Kim, Fei Zhou, Arne-Heike Meissner-Schenk,
Michael Peter, Geunmin Ryu, David A . Schleuning,
Coherent, Inc . (United States)
We report on our progress developing long wavelength high power laser diodes based on the InGaAsP/InP alloy system emitting in the range from
1400 to 2010 nm. Output power levels exceeding 50 Watts CW and 40% conversion efficiency were obtained at 1470 nm wavelength from 20% fill factor (FF) bars with 2 mm cavity length mounted on water cooled plates.
Using these stackable plates we built a water cooled stack with 8 bars, successfully demonstrating 400 W at 1470 nm with good reliability. In all cases the maximum conversion efficiency was greater than 40% and the maximum power achievable was limited by thermal rollover. For lasers emitting in the range from 1930 to 2010 nm we achieved output power
9733-8, Session 2
Yohei Kasai, Shinichi Sakamoto, Yukihiko Takahashi,
Ken Katagiri, Fujikura Ltd . (Japan); Yuji Yamagata,
OPTOENERGY Inc . (Japan); Akira Sakamoto, Daiichiro
Tanaka, Fujikura Ltd . (Japan)
High-brightness fiber-coupled laser diode module is one of the most important devices for high-power fiber laser systems. Fibers with 100 um core diameter are widely used for these modules because their cladding diameters are the same as fibers used in telecommunication market and they are easy to handle. The power up to only 150 W is commercially available with 100 um fibers, and 200 um core size is needed for higher power modules.
We have overcome this limitation and achieved optical output power over
300 W with 100 um / NA 0.22 fiber by integrating the several tens of optimally-designed single emitter laser diodes in a newly designed package.
We employed unique design such as Asymmetric Decoupled Confinement
Heterostructure (ADCH) and the stripe width to increase the durability for the catastrophic optical damage.
The beams from each laser diode are aligned precisely by optimallydesigned lenses and mirrors, especially pitch of stacked beam along the fast axes and the current dependence of the divergence angle of the slow axes. In addition, polarization multiplex technique is used to double the brightness.
High-heat conducting materials are used as base materials of the module package to reduce the thermal resistance of the module. The junction temperature of the laser diode is suppressed and high-power and highreliability laser diode modules are obtained. As a result, over 300 W power are achieved without thermal rollover at 16 A.
The high-brightness modules have a great advantage for high power fiber lasers such as 10 kW and beyond.
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Conference 9733: High-Power Diode Laser
Technology and Applications XIV
9733-9, Session 2
Andreas Bayer, Andreas Unger, Bernd Köhler, Matthias
Küster, Sascha Dürsch, Heiko Kissel, Jens Biesenbach,
DILAS Diodenlaser GmbH (Germany)
The demand for high brightness fiber coupled diode laser devices in the multi kW power region is mainly driven by industrial applications for materials processing, like metal welding, which requires a beam quality better than 30 mm x mrad. Reliability, modularity, and cost effectiveness are key factors for success in the market. We have developed a scalable and modular diode laser architecture that fulfills these requirements through use of a simple beam shaping concept based on two dimensional stacking of tailored diode bars mounted on specially designed, tap water cooled heatsinks.
For a single wavelength, up to eight of these building blocks, implying a total of 32 tailored bars, can be stacked into a submodule, polarization multiplexed, and coupled into a 400 µ m, 0.12NA fiber. Output power of such a submodule is more than 1 kW with an electro-optical efficiency above
50%. Due to the simple beam shaping concept, the majority of the optical alignment processes inside the submodule are fully automated to guarantee constant quality, reliability, and a cost-efficient production process.
Scalability into the multi kW region is realized by wavelength combining of replaceable submodules in the spectral range from 900 – 1100 nm. We present results of a laser source based on this architecture with an output power of more than 4 kW and a beam quality of 25 mm x mrad.
As applications for diode lasers in the fields of solid-state pumping, fiber laser pumping, and materials processing continue to demand higher power and brightness, there is a strong market for highly efficient, lightweight diode pump modules. Many of these applications, such as airborne or field transportable systems, require a high degree of mobility, while others may simply benefit from lower module size where space is at a premium. We present an update on several lightweight diode pump modules with power output in the range of 600W to almost 1kW, weight-to-power ratio (WPR) from 0.9 to 0.7 kg/kW, and electro-optical efficiencies well in excess of 50%.
DILAS has previously reported on the IS46, a successful pumping product with a 300W output from a ~300g module and many hundred modules in the field. Here we present an updated version of the IS46 providing ~350W output power at the same weight. Also presented are updated results from the previously reported IS53 module, which now shows 600W of output, and data from a new prototype capable of producing nearly 1kW from a 225um, 0.22NA fiber. The basic technologies that allow such compact systems will be discussed, with special emphasis on the engineering challenges of high efficiency, lightweight system design. In particular, primary drivers that allow high optical efficiency, the management of waste heat, and the design of the associated laser cooling architecture will be reviewed.
9733-12, Session 3
Manoj Kanskar, Ling Bao, Zhigang Chen, David Dawson,
Mark DeVito, Weimin Dong, Mike P . Grimshaw, Xinguo
Guan, Marty Hemenway, Keith Kennedy, Rob Martinsen,
Wolfram Urbanek, Shiguo Zhang, nLIGHT Corp . (United
States) 9733-10, Session 3
Jay Skidmore, Matthew Peters, Victor Rossin, James Guo,
Yan Xiao, Jane Cheng, Allen Shieh, Raman Srinivasan,
Jaspreet Singh, Cailin Wei, Richard Duesterberg, James J
Morehead, Erik Zucker, Lumentum (United States)
Laser diodes with high brightness and low cost are critical for pumping kW-class fiber lasers. The ST-series multi-emitter 9XXnm fiber-coupled pump platform was previously designed to balance reliable output power with suitable brightness (i.e., 140W ex-fiber, 105um core, with > 95% power into 0.15NA). The goal of the present study is to reduce pump count by increasing the diode power level, while maintaining a similar brightness level of the ST pump. In this way, we can reduce the total pump cost (in terms of
$/W) at the system level. Laser diodes are spatially multiplexed into a 135um diameter core fiber. The package architecture leverages the same optical train and mechanical structure that was qualified previously. As compared to
ST form factor, the package is extended by < 1”, whereas the height, width and bolt pattern remain unchanged for backward compatibility. With the latest-generation laser diode pump platform, we have achieved 250W CW power at 22A at ~ 30C case temperature. The power conversion efficiency is 55% (peak) that drops to 47% at 22A with little thermal roll over. Greater than 95% of the light is collected at < 0.15NA at 16A drive current.
There is an increasing demand for high-power, high-brightness diode lasers at 885 nm, 915 nm and 976 nm for applications such as fiber laser pumping, materials processing, solid-state laser pumping, and consumer electronics manufacturing. The kilowatt CW fiber laser pumping (915 nm for industrial fiber lasers & 976 nm for directed energy fiber amplifiers) particularly requires the diode lasers to have both high power and high brightness in order to achieve high-performance. This paper presents our continued progress in the development of high power and high brightness fiber-coupled product platform, element, to address these applications.
Recent improvements in fiber-coupled power has been enabled by significant advances in the slow-axis brightness of broad area lasers. We have demonstrated slow-axis brightness as high as 4.3 W/mm-mrd resulting from reducing the number of allowed modes in the slow-axis direction.
Further improvement is underway. This new generation of reduced-mode diodes (REM-diodes) have half the slow-axis divergence compared to regular BALs at the same operating powers. As a result, we have achieved
>160 watts from a 2?6 element module in the 9xx nm spectral range out of a 105 µ m/0.15 NA beam. We have also extended the REM concept to geometrically multiplexing multiple of these devices to scale up power at higher BPP. We will present performance and reliability data on these devices. Further slow-axis brilliance improvement is underway and we will report the latest findings.
9733-11, Session 3
David A . Irwin, DILAS Diode Laser, Inc . (United States)
9733-13, Session 3
Tobias P . Koenning, Dan McCormick, David A . Irwin, Dean
Stapleton, Tina Guiney, Steve G . Patterson, DILAS Diode
Laser, Inc . (United States)
Due to their low quantum defect, diode pumped alkali metal vapor lasers
(DPALs) offer the promise of scalability to very high average power
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Conference 9733: High-Power Diode Laser
Technology and Applications XIV
(Germany) levels while maintaining excellent beam quality. Research on DPALs has progressed to ever increasing power levels across multiple gain media species over the last years, necessitating pump power in the kW range. Each material requires a specific pump wavelength: near 852 nm for cesium, 780 nm for rubidium, 766 nm for potassium, and 670 nm for lithium atoms. The shorter pump wavelength below 800nm are outside the typical wavelength range for pump diodes developed for diode pumped solid state lasers
(DPSS).
The biggest challenge in pumping these materials efficiently is the need for maintaining the narrow gain media absorption band of approximately 0.01 nm while greatly increasing power. Typical high power diode lasers achieve spectral widths around 3nm (FWHM) in the near infrared spectrum, but optical gratings may be used internal or external to the cavity to reduce the spectral width. Recently, experimental results have shown yet narrower line widths ranging from picometers at very low power levels to sub-100 picometers for water cooled stacks around 1kW of output power.
The focus of this work is the development of a fiber-based pump system for potassium DPAL. The individual tasks are the development of high power
766nm chip material, a fiber-coupled module as a building block, and a scalable system design to address power requirements from hundreds of watts to tens of kilowatts. Results for a 3kW system achieving ~30GHz bandwidth at 766nm will be shown. Approaches for power-scaling and size reduction will be discussed.
We present our building block system concept, which consists of 500 W building blocks, which will be stacked via variations of combining methods to multi kW systems, while enabled easy field maintenance.
The key subassembly is a structure consisting of single emitters, automatically aligned individual fast axis collimation lenses and a monolithic slow axis collimation and redirection device. By varying the diode wavelengths they can later be combined by various techniques and therefore power scaled. The diodes on a subassembly are vertically stacked, can be wavelength stabilized and lead to an output power of well above 100 W with BPP of <3.5 x 5 mm*mrad (fast x slow axis). These base modules now can be further power scaled by combinations of polarization and wavelength multiplexing, which results in building blocks with > 500 W optical output power within a 100 µ m fiber with 0.15 NA or by combination of several building blocks up to multi kW systems without change in beam quality.
In addition the built-in electronics is monitoring, controlling and diagnosing each individual wavelength channel via, further more due to the 48 V architecture and only 12 A per channel, the laser systems are capable of short µ s pulses up to cw.
The combination of this intelligent electronics with industrial interfaces as
TCP/IP, which allows remote control and –diagnostic, and the building block concept enables easy and sustainable field maintenance.
9733-14, Session 4
Baohua Wang, Weirong Guo, Zhijie Guo, Dan Xu, Jing Zhu,
Qiang Zhang, Thomas C . Yang, Xiaohua Chen, BWT Beijing
Ltd . (China)
Spectral beam combination expands the output power while keeps the beam quality of the combined beam almost the same as that of a single emitter. Spectral beam combination has been successfully achieved for high power fiber lasers, diode laser arrays and diode laser stacks. We have recently achieved the spectral beam combination of multiple single emitter diode lasers. Spatial beam combination and beam transformation are employed before beams from 25 single emitter diode lasers can be spectrally combined. An average output power about 220W, a spectral bandwidth less than 9 nm (95% energy), a beam quality similar to that of a single emitter and electro-optical conversion efficiency over 46% are achieved.
In this paper, Rigorous Coupled Wave analysis is used to numerically evaluate the influence of emitter width, emitter pitch and focal length of transformation lens on diffraction efficiency of the grating and spectral bandwidth.
To assess the chance of catastrophic optical mirror damage (COMD), the optical power in the internal cavity of a free running emitter and the optical power in the grating external cavity of a wavelength locked emitter are theoretically analyzed.
Advantages and disadvantages of spectral beam combination are concluded.
9733-16, Session 4
µ
Ulrich Witte, Martin Traub, Angelo Di Meo, David Rubel,
Marcus Hamann, Stefan Hengesbach, Hans-Dieter
Hoffmann, Fraunhofer-Institut für Lasertechnik (Germany)
We present a compact, modular and cross talk free approach for dense wavelength division multiplexing of high power diode lasers based on ultrasteep dielectric filters. The filters are characterized in a newly developed characterization stage and have a band edge steepness of approximately
0.7 nm. One submodule consists of two mini bars that are geometrically stacked in the fast axis (FA). The collimated beams of the individual emitters are subsequently spectrally combined by use of dielectric filters. For fiber coupling, a rotationally symmetric focusing lens is utilized. The mini bars consist of 5 narrow stripe broad area (NBA) emitters with a beam parameter product in the range of 2 mm mrad and a wavelength spacing of 2.5 nm between 2 adjacent emitters. The near field with of the emitters is 30 µ m up to 40 µ m. Internally stabilized DFB-NBA laser diodes are compared with AR-coated and externally stabilized NBA laser diodes. For external stabilization one partially reflective mirror is used to build an external selflocking cavity. Experimental results for fiber coupling (35 µ m core diameter,
NA < 0.18) of internally and externally stabilized diode lasers are presented.
Additionally, optical losses are analyzed and alternative optical designs to overcome the current limitations of the setup are discussed.
9733-15, Session 4
Andreas Grohe, Fabio Ferrario, Haro Fritsche, Thomas
Hagen, Holger Kern, Ralf Koch, Bastian Kruschke, Axel
Reich, Dennis Sanftleben, Ronny Steger, Till Wallendorf,
Wolfgang Gries, DirectPhotonics Industries GmbH
9733-17, Session 4
Guillaume Schimmel, Ioana Doyen, Sylvie Janicot, Marc
Hanna, Patrick Georges, Gaëlle Lucas-Leclin, Lab . Charles
Fabry (France); Jonathan Decker, Paul Crump, Goetz
Erbert, Ferdinand-Braun-Institut (Germany); Simeon
Kaunga-Nyirenda, Daniel Moss, Steve Bull, Eric Larkins,
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Conference 9733: High-Power Diode Laser
Technology and Applications XIV
The Univ . of Nottingham (United Kingdom)
Coherent Beam Combining (CBC) consists in superposing several beams that are coherent with each other, thereby generating a single high-power laser beam with excellent spectral and spatial properties. We investigate a new CBC architecture using a common laser external cavity on the back side of the emitters for phase locking, while coherent beam superposition of phase-locked beams is realized on the front side. This technique leads to a separation of the phase-locking stage – which takes place in the common external cavity on the rear side of the lasers - and the beam combining stage – which is achieved on the front side outside the cavity. In this contribution, this technique is applied to high-brightness tapered devices demonstrating the potential of extended-cavity phase-locking arrangements for high-power operation.
The rear-side common resonator used for phase-locking of the two emitters is a passive external cavity designed as a Michelson interferometer.
The phase-locking range and the resistance of the external cavity to perturbations are investigated. On the front side the combining efficiency is above 80% and results in an output power of 6.5 W in a nearly diffractionlimited beam (M?(4?) ≤ 1.2). The corresponding electrical-to-optical efficiency is above 20%. The combined power is stabilized with an automatic adjustment of the driving currents.
9733-18, Session 4
Dan Yanson, Noam Rappaport, Ophir Peleg, Yuri Berk, Nir
Dahan, Genady Klumel, Ilya Baskin, Moshe Levy, Yoram
Karni, SCD SemiConductor Devices (Israel)
Wavelength-stabilized high-brightness single emitters are commonly used in fiber-coupled laser diode modules for pumping Yb-doped lasers at 976 nm, and Nd-doped ones at 808 nm. We investigate the spectral behavior of single emitters under wavelength-selective feedback from a volume Bragg
(or volume hologram) grating (VBG) in a multi-emitter module.
By integrating a full VBG model as a multi-layer thin film structure with commercial raytracing software, we simulated wavelength locking conditions as a function of beam divergence and angular alignment tolerances. Good correlation between the simulated VBG feedback strength and experimentally measured locking ranges, in both angle and laser temperature, is demonstrated.
The challenges of assembling multi-emitter modules based on beamstacked optical architectures are specifically addressed, where a common
VBG is placed to wavelength-lock all emitters together. The wavelength locking conditions must be achieved simultaneously with a high fiber coupling efficiency for each emitter in the module. It is shown that even a minor angular misorientation between fast and slow-axis collimating optics can have a dramatic effect on the spectral and power performance of the module.
We report on the progress towards development of a wavelength-stabilized fiber laser pump module, which uses a VBG to provide wavelength-selective optical feedback in the collimated portion of the beam. Powered by our purpose-developed high-brightness single emitters, the module reaches 45
W output from a 105 µ m core, 0.15 NA fiber with an 0.3 nm linewidth at a wavelength of 976 nm. Preliminary wavelength-locking experiments at 808 nm are also presented.
9733-19, Session 4
Stefan Hengesbach, Sarah Klein, Carlo Holly, Ulrich Witte,
Martin Traub, Hans-Dieter Hoffmann, Fraunhofer-Institut für Lasertechnik (Germany)
Multiplexing technologies enable the development of high-brightness diode lasers for direct industrial applications. We present a compact
High-Power Dense Wavelength Division Multiplexer (HP-DWDM) with an average channel spacing of 1.7 (1.5) nm and a subsequent external cavity mirror to provide feedback for frequency stabilization and multiplexing in one step. The „self-locking“ multiplexing unit consists of four Volume
Bragg Gratings (VBGs) with 99% diffraction efficiency and seven dielectric mirrors to overlay the radiation of five input channels with an adjustable channel spacing of 1-2 nm. In detail, we focus on the analysis of the overall optical efficiency and the change of the beam parameter product and the spectral width. The performance is demonstrated using five 100 microns wide multimode 9xx single emitters with M2 ≤ 17. Because of the feedback the lateral (multimodal) spacial and angular intensity distribution changes strongly and the beam parameter product decreases by a factor of 1.2 to
1.9. Thereby the angular intensity distribution is more affected than the near field intensity distribution. The spectral width per emitter decreases to
3-200 pm (FWHM) depending on the injection current and the reflectance of the feedback mirror (0.75%, 1%, 2%, 4% or 6%). Thus, the laser bandwidth is much smaller than the wavelength selectivity of the Volume Bragg Grating due to gain narrowing and an optimized feedback strength. The overall optical multiplexing efficiency ranges between 77% and 86%. With some modifications (e.g. enhanced AR coatings) we expect 90-95%.
9733-20, Session 5
(Invited Paper)
Carlo F . Frevert, Frank Bugge, Steffen Knigge, Arnim
Ginolas, Götz Erbert, Paul Crump, Ferdinand-Braun-Institut
(Germany)
Both high-energy-class laser facilities and commercial high-energy pulsed laser sources require reliable optical pumps with the highest pulse power and electro-optical efficiency. Although commercial quasi-continuouswave (QCW) diode laser bars reach output powers of 300…500W further improvements are urgently sought to lower the cost per Watt, improve system performance and reduce overall system complexity. Diode laser bars operating at temperatures of around 200K show significant advances in performance, and are particularly attractive in systems that use cryogenically cooled solid state lasers. We present the latest results on
940nm, passively cooled, 4mm long QCW diode bars which operate under pulse conditions of 200?s, 10Hz at an output power of 1kW with efficiency of 70% at 203K: a two-fold increase in power compared to 300K, without compromising efficiency. We discuss how custom low-temperature design of the vertical layers can mitigate the limiting factors such as series resistance while sustaining high power levels. We then focus on the remaining obstacles to higher efficiency and power, and use a detailed study of multiple vertical structures to demonstrate that the properties of the active region are a major performance limit. Specifically, one key limit to series resistance is transport in the layers around the active region (resistance is a
110 SPIE Photonics West 2016 · www.spie.org/pw
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clear function of well depth) and the differential internal efficiency is closely correlated to the transparency current density. Tailoring the barriers around the active region and reducing transparency current density thus promise bars with increased performance at temperatures of 200K as well as 300K.
9733-21, Session 5
Conference 9733: High-Power Diode Laser
Technology and Applications XIV
Alex Kindsvater, Matthias Schroeder, Ekkehard A . Werner,
Sebastian Seidel, Martin Woelz, Valentin Loyo, JENOPTIK
Laser GmbH (Germany)
High duty-cycle, high-efficiency QCW stacks are ideally suited for medical and cosmetic applications. The 8-bar stack with a bar-to-bar pitch of 1,7mm emits 808 or 940nm wavelength with 65 to 95 Joule depending on pulse conditions at 25°C water temperature. The value is limited by thermal effects and can be increased by choosing the lower limit of the cooling specification. This stack is specified for up to 130 A at 50ms, 15% d.c., down to 45 A at 400ms, 55% d.c. The reliability for long pulse operation is targeted to reach up to 450 hours of total life time. That is equivalent to 15
Mshots at pulse durations less or equal 100ms or 4 Mshots at 400ms. The stack heat sink is cooled by filtered tap water at 15 – 25°C with flow rates of up to 0.9 ±0.1 l/min at inlet pressures up to 1.7 ±0.1 bar. Efficiency, thermal impedance and wavelength plots are presented in the paper.
output powers Popt > 10W with efficiency > 60%. However, their application is limited due to poor in-plane beam parameter product
BPPlat=0.25?FF95%?w95% (FF95% and w95% are emission angle and aperture, 95% power content). We present progress in improving BPPlat by choosing the proper vertical designs. First, we show that large vertical asymmetry is beneficial, with extreme-double-asymmetric (EDAS) waveguide designs delivering a ~1 mm?mrad reduction in the BPP ground level, compared to a reference (more symmetric) design. Possible reasons include a reduced number of lateral modes, a modified thermal lens profile or an improvement in the beam quality of the individual modes. Measured thermal profiles show no clear evidence for a difference in the lateral thermal lens when EDAS designs are used and 2-D waveguide simulation based on the profiles shows no significant difference in confinement factor of higher order modes. Therefore, the improved BPPlat is most likely due to an improvement in the lateral mode quality. Second, we test the benefit of low modal gain factor Gg0, predicted to improve BPPlat via a suppression of filamentation. EDAS-based lasers with single and double quantum well active regions were compared, with 2.5x reduced Gg0, for 2.2x reduced filament gain. However, no difference is seen in measured BPPlat, giving evidence that filamentary processes are no longer a limit. In contrast, devices with lower Gg0 demonstrate an up to twofold reduced near field modulation depth, potentially enabling higher facet loads and increased device facet reliability.
9733-22, Session 5
Wentao Guo, Manqing Tan, Institute of Semiconductors
(China)
9733-24, Session 5
Nikolay Ledentsov, Vitaly A . Shchukin, VI Systems GmbH
(Germany); Mikhail V . Maximov, Nikita Y . Gordeev, Nikolay
A . Kaluzhniy, Sergey A . Mintairov, Alexey S . Payusov, Yuri
M . Shernyakov, Ioffe Physical-Technical Institute (Russian
Federation)
The 980nm semiconductor lasers are the important pump sources of the
Erbium-Doped Fiber Amplifier (EDFA) and Erbium-Doped Superfluorescent
Fiber Source (ED-SFS). They have important significance to the high speed, large capacity, long distance all-optical communication systems and the high-precision fiber optic gyroscope (FOG). The asymmetric twin waveguide
(ATG) technology was used to prepare the 980nm FP cavity semiconductor lasers and the spot size converter integrated devices. The SSC-LD equivalent resonator model has been established to do the theoretical calculation of the coupling coefficient and gain coefficient. The design of the device structure has been optimized by researching the influencing mechanism of tapered waveguide’s shape and the epitaxial layer’s structure parameters on the output characteristics of the devices. The technical scheme of SSC-LD’s preparation has been studied on using ATG technology. Finally, the sample with the center wavelength of 980nm±3nm, less than 10° for vertical farfield divergence angle has been made in the experiment.
9733-23, Session 5
Martin Winterfeldt, Steffen Knigge, André Maaßdorf,
Ferdinand-Braun-Institut (Germany); Martin Hempel,
Jens W . Tomm, Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie (Germany); Götz Erbert, Paul
Crump, Ferdinand-Braun-Institut (Germany)
GaAs-based high-power broad-area diode lasers deliver NIR optical
Thick waveguide laser diodes allow a reduced impact of the catastrophic optical mirror damage and thermal “smile” effects in laser chips and bars.
Tilted Wave Lasers (TWLs) [1] based on optically coupled thin active and thick passive waveguides may offer an ultimate solution, in which the thickness of the passive waveguide can vary from ~10–35 um realized by an epitaxial layer [2] and up to ~100–150 um [2] if a transparent substrate is employed as the passive waveguide. Two vertical lobe emission has an advantage for the application in coherent laser stacks, based on external glass plate reflector. We show that by proper engineering of the waveguide one can realize high performance TWL diodes at different tilt angles of the lobes (e.g., +/–27 degrees or +/–9 degrees) to the junction plane. The TWL with the lobes at +/–9 degrees allows above 95% of the power to be emitted within a vertical angle below 25 degrees, which is important for laser stack applications also using conventional optical coupling schemes. A single lobe emission at zero angle can be realized. A high differential efficiency
~90% and a current–source limited pulsed power >42W for as–cleaved TWL device at a cavity length of 1.5 mm and a stripe width of 50 um is shown.
Thus the power per facet length in a laser bar in excess of 8.4 kW/cm can be reached.
The work was supported by ZIM Program of BMWi (Project COLIBRI).
[1] N. N. Ledentsov, et al., Electron. Lett. 47, 1339–1340 (2011)
[2] N. N. Ledentsov, et al., Proc. SPIE 8965, 89650Q (2014)
9733-25, Session 5
Jukka Viheriälä, Joel Salmi, Tampere Univ . of Technology
(Finland); Jaakko M . Mäkelä, Univ . of Turku (Finland);
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Conference 9733: High-Power Diode Laser
Technology and Applications XIV
Antti T . Aho, Heikki A . Virtanen, Tomi Leinonen, Mihail M .
Dumitrescu, Mircea Guina, Tampere Univ . of Technology
(Finland)
Lecomte, Olivier Parillaud, Michel Krakowski, III-V Lab .
(France)
We report the development and the performance of 1550 nm tapered
DBR laser diodes. These devices are particularly attractive for applications requiring eye-safe high power single-mode operation, such as LIDAR and range-finding. The DBR was fabricated using a regrowth-free process based on surface gratings and InP/AlGaInAs QWs. A CW output power as high as 400 mW in single-mode operation was achieved at room-temperature.
At maximum output power the SMSR was 45 dB, proving the excellent behavior of the surface gratings.
The ridge waveguide and DBR surface grating were defined using soft-UV-
NIL, while the patterning of metals and dielectrics was done using regular
UV-lithography. This “mix-and-match” processing technique combines the best from both lithography methods. To our knowledge this is the first demonstration of DBR lasers fabricated using soft-UV-NIL on wafer-scale.
The processed chips consisted of a 1 mm long DBR-grating section, a 1 mm long straight ridge waveguide section and a tapered section with 6 degrees full opening angle. The length of the tapered section has been varied between 0.5 mm and 1.85 mm to study the power scalability. For characterization the chips were p-side-down mounted on an AlN170submount containing multiple electrically isolated AuSn-pads, which enabled driving each laser section separately.
By increasing the length of tapered section from 0.5 mm to 1.85 mm the maximum CW power at room temperature could be scaled from 125 mW to 400 mW. The design guidelines and power scaling capabilities will be discussed.
The request of high power diode lasers in the range of 910-980nm is growing. This kind of device has many applications, such as fiber laser pumping, material processing, solid-state laser pumping, defense and medical/dental applications. The key role of this device lies in the wall plug efficiency (?e ) of converting electrical power into optical power. The high value of ?e allows high power level and reduces the level of current heating in lasers. The need of wavelength thermal stabilization is more evident in the case of multimode 975nm diode lasers used for pumping the Yb, Er and Yb/Er co-doped solid-state laser, which has a narrow absorption line close to 975nm. Narrow spectral width operation (<1 nm), combined with thermal stabilization (0.07 nm/°C), is achievable in the high power diode laser using an optical feedback provided by a uniform distributed feedback grating (DFB), introduced via etching and re-growth techniques into the semiconductor layers. We present the laser structure (Al-free in the active region) and the process techniques necessary to define the gratings into the structure. We will draw attention onto our performance in term of spectral response (SMSR>45dB with a width <1nm), the internal parameters (low internal losses ~1 1/cm, dP/dI~1 W/A, Rs~40m?), the measurement of thermal resistance (Rth ) (for the first time with high power laser diode at 975nm) the T3ster equipment, and the thermal simulation in order to understand the heat distributions and the eventually bottleneck.
9733-28, Session 6
John M . Morales, Sami Lehkonen, David A . Schleuning,
Bruno Acklin, Coherent, Inc . (United States)
9733-26, Session 6
Agnieszka Pietrzak, Ralf Hülsewede, Martin Zorn,
JENOPTIK Diode Lab GmbH (Germany); Jens Meusel,
JENOPTIK Laser GmbH (Germany); Jürgen Sebastian,
JENOPTIK Diode Lab GmbH (Germany)
Single emitters emitting at a wavelength around 808 nm are highlydesired as pump sources of low power solid state lasers which are widely utilized e.g., in micro-marking, metrology-instrumentation, and for build compact NIR-light sources. For this wavelength region different quantumwell material can be used resulting in different polarization directions. We present the latest development of high-power single emitters having emitter apertures of 95 µ m, 100 µ m and 200 µ m based on TM-polarized material.
Furthermore, different cavity length of 2 mm and 4 mm are investigated.
Short-cavity devices were characterized up to powers over 4 W with a wall plug efficiency above 60%. Long-cavity devices were characterized up to their maximum optical output power of 15 W from 100 µ m wide emitters and 22 W from 200 µ m wide emitters with 4 mm cavity length mounted on passively cooled heat-sinks. The operation point of these devices is 8 W and 12 W, respectively with wall-plug efficiencies of ~55%. Furthermore first results on 5-emitters bars are presented operating at 40 W.
9733-27, Session 6
Roberto Mostallino, Michel Garcia, III-V Lab . (France);
Yannick Deshayes, Univ . Bordeaux 1 (France); Alexandre
Larrue, Yannick Robert, Eric Vinet, III-V Lab . (France);
Laurent Bechou, Univ . Bordeaux 1 (France); Michel
Key applications for 780-830nm high power diode lasers include the pumping of various gas, solid state, and fiber laser media; medical applications including hair removal; direct diode materials processing; and computer-to-plate (CtP) printing. Many of these applications require high brightness fiber coupled beam delivery, requiring high brightness optical output at the bar and chip level. Many require multiple bars per system, with aggregate powers on the order of kWs, placing a premium on high wallplug efficiency. This paper presents Coherent’s recent advances in the production of high brightness, high efficiency bars and chips at 780-830nm. Results are presented for bars and single emitters of various geometries. Performance data is presented demonstrating peak wallplug efficiencies of 64% in CW mode. Reliability data is presented demonstrating >>20k hrs reliability for products including 60W 18% fill factor and 80W 28% fill factor conduction cooled bars.
9733-29, Session 6
Mico Perales, MH GoPower Co ., Ltd . (United States); Meihuan Yang, John Wu, Talan Hsu, MH GoPower Co ., Ltd .
(Taiwan); Wei-sheng Chao, MH GoPower Co ., Ltd . (Taiwan) and MH GoPower Co ., Ltd . (Taiwan); Kun-hsien Chen, MH
GoPower Co ., Ltd . (Taiwan) and MH GoPower Co ., Ltd
(Taiwan); Terry Zahuranec, MH GoPower Co ., Ltd . (United
States)
Continuing improvements in the cost and power of laser diodes have been critical in launching the emerging fields of power over fiber (PoF), and laser power beaming. Laser power is transmitted either over fiber (for PoF), or through free space (power beaming), and is converted to electricity by photovoltaic cells designed to efficiently convert the laser light. MH
112 SPIE Photonics West 2016 · www.spie.org/pw
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GoPower’s (MHGP) VMJ PV cell, designed for high intensity photovoltaic applications, is fueling the emergence of this market, by enabling unparalleled photovoltaic receiver flexibility in voltage, cell size, and power output. Our research examines the use of the VMJ cell in these laser power transmission applications. We first fully characterize the performance of the VMJ cell under various laser conditions, including multiple near IR wavelengths, multiple light intensities ranging from mW to tens of watts per cm2, and different beam uniformities. We also investigate the impact of the physical dimensions (length, width, and height) of the VMJ cell on its performance. We then delve deeper into VMJ cell performance within the power over fiber application, as we examine the effectiveness of the
VMJ cell in various receiver packages that deliver target voltage, uniformity, intensity, and power levels. By designing and characterizing multiple receivers, we illustrate techniques for packaging the VMJ cell for achieving optimal performance and target voltages, as well as minimizing package size, for power over fiber applications.
9733-30, Session 7
Conference 9733: High-Power Diode Laser
Technology and Applications XIV
Holger Moench, Ralf Conrads, Stephan Gronenborn, Philips
Technologie GmbH (Germany); Xi Gu, Philips Lighting
B .V . (Netherlands); Michael Miller, Philips GmbH U-L-M
Photonics (Germany); Pavel Pekarski, Jens Pollmann-
Retsch, Philips Research (Germany); Armand Pruijmboom,
Philips Lighting B .V . (Netherlands); Ulrich Weichmann,
Philips Technologie GmbH (Germany)
Fraunhofer-Institut für Produktionstechnologie IPT
(Germany)
In this paper we present an industrial grade assembly solution for micro optics utilized in high power diode laser stacks.
With ever-rising demand for HPDL-stacks higher degrees of automation are becoming economically viable solutions. Proven assembly technology and concepts can be transferred from close industrial domains as a starting point but need to be extended for a successful application in laser industry.
Quality demands of micro optics in high-power environments cannot be satisfied with geometric specification alone; hence alignment tasks of optical components often focus on the optimization of product functions instead. The integration of these domain specific active alignment algorithms and measurement setups in classic industrial automation environments are main challenges when moving towards highly automated solutions.
Stack assembly is additionally demanding as measurement equipment and current stack level need to be synchronized during the assembly.
Furthermore laser bars are individually contacted to reduce heat progression and excessive laser radiation.
We will present a detailed analysis of integration challenges and viable approaches in regard to software, compact measurement equipment for active alignment and unbroken process observation for optimized shrinkage compensation based on calculated quality metrics. Furthermore we analyze the process capability and cycle times of an automated FAC assembly for stacks.
9733-32, Session PTue
Shir Shahal, Hamootal Duadi, Moti Fridman, Bar-Ilan Univ .
(Israel)
High power VCSEL system technology extends to proper coolers, bonding technology and integrated optics i.e. far beyond the VCSEL chip itself. The paper discusses high performance components and processes dedicated to the needs of VCSEL array chips in high power systems. New approaches help to eliminate components and process steps and make the system more robust and easier to manufacture.
Densely packed high power systems rely on perfectly matched microchannel coolers. New cooler concepts with integrated electrical and mechanical interfaces have been investigated and offer advantages for high power system design.
The bonding process of chips on sub-mounts and coolers has been studied extensively and for a variety of solder materials. High quality of the interfaces as well as good reliability under normal operation and thermal cycling have been realized. A viable alternative to soldering is sintering with a silver paste. The very positive results which have been achieved with rather different technologies indicate the robustness of the VCSEL chips and the suitability for high power systems.
Beam shaping micro-optics can be integrated on the VCSEL chip in a wafer scale process by replication of lenses in a polymer layer. The performance of VCSEL arrays with integrated collimation lenses has been positively evaluated and the integrated chips are fully compatible with all further assembly steps.
The integrated high power systems make the application even easier and more robust. New examples in laser material processing and pumping of solid state lasers will be presented.
9733-31, Session 7
Daniel Zontar, Fraunhofer-Institut für
Produktionstechnologie IPT (Germany); Harald Vogt,
MA micro automation GmbH (Germany); Sebastian
Haag, Tobias Müller, Sebastian Sauer, Christian Brecher,
High efficiency, compact size and low price are some of the reasons for the wide spreading of high-power laser diode bars. However, laser diode bars have low beam quality due to their multiple emitters. One way to overcome this drawback is to obtain phase locking of the different emitters of the diode bar, which increases the beam quality and enables a smaller focused beam. Phase locking of diode lasers was previously demonstrated by Talbot effect [1], and off axis coupling [2]. However, these coupling methods work only for periodic emitters.
We demonstrate passive phase locking technique of laser diode bars which is robust, stable and works with non-periodic diode bar emitters. We built a degenerate diode laser cavity of 906 nm wavelength and placed two CCD cameras for measuring the near field and far field intensity distributions.
The degenerate cavity contains a diode bar with antireflection coating, a
4-f system and an output coupler. In order to phase lock the emitters of the diode bar, we insert a varying aperture into the focal plane of the 4-f system
[3]. We measured the output beam quality and power as a function of the aperture width. Our results show that the beam quality can be improved by a factor of 2.7 with reduction of less than 30% of the output power. These results can lead to novel high power diode lasers with increased beam quality. The full experimental details and results will be presented.
References:
1. V. V. Apollono, S. I. Derzhavin, V. A. Filonenko et al. “High power laser diode array phase-locking” SPIE, 3889,134 (2000).
2. Z. Su, Q. Lou, J. Dong, J. Zhou and R. Wei, “Beam quality improvement of laser diode array by using off-axis external cavity” Opt. Express, 15, 11776
(2007).
3. N. Davidson, M. Nixon, E. Ronen, M. Fridman, and A. Friesem, “Phase locking large arrays of lasers” in Conference on Lasers and Electro-Optics
2012, OSA Technical Digest (online) (Optical Society of America, 2012), paper CTu3N.7.
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Conference 9733: High-Power Diode Laser
Technology and Applications XIV
9733-33, Session PTue
Hongyue Gao, JIcheng Liu, Shanghai Univ . (China)
Our work focuses on static and dynamic holographic 3D display bases on laser recording and reconstruction. Laser plays an important role in holography, and provides wider color than LED display. In this paper we will present some work on 3D hologram print and holographic 3D video display in materials, which aims at future 3D pictures and 3D displayers, because holography is a true 3D technique. Computer generated holograms, holographic storage materials, and hologram print system in holographic print study will be introduced. Furthermore, real time dynamic holographic 3D display in materials, which may be developed in holographic 3D televisions or holographic 3D projectors in future, will also be presented. More important, this is a very typical laser application because developments of holographic 3D displayers depend on development of lasers. We hope that more and more lase experts can pay attention to holographic 3D display by this presentation, and the holographic display can come into our lives as soon as possible, since holographic 3D display, as a true 3D display, has huge application area.
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9734-1, Session 1
(Invited Paper)
Mark E . Kuznetsov, AXSUN Technologies Inc . (United
States)
Semiconductors have been used as laser gain medium since the earliest days of lasers. Current injection of carriers across a diode p-n junction has been the preferred way to pump such lasers, leading to the ubiquitous diode lasers used across a wide range of applications. Optical pumping of semiconductor lasers has also been used through the years, but mostly as a research tool on the path to the ultimately electrically pumped version.
In the mid 1990s, a group led by Aram Mooradian in a small startup company Micracor demonstrated Optically Pumped Semiconductor Lasers
(OPSL) with remarkable properties that led to their rapid development and wide use in research and industrial applications. Using vertical cavity configuration emitting light normal to the plane of the wafer, and applying an external mirror to stabilize a large area fundamental transverse mode, optical pumping allowed operation of watt-class lasers with excellent beam quality and wide wavelength coverage enabled by the bandgap-engineered semiconductor media. These Vertical External Cavity Surface Emitting
Lasers (VECSEL) proved to be so versatile, that arrayed electrically-pumped version of these lasers, NECSEL, was developed in another startup company,
Novalux, led again by Aram Mooradian. In this presentation I will describe our early work on OPSLs at Micracor, where we took the dreams of a new remarkable laser and found a path to make them a reality. We also remember Aram Mooradian as a person and scientist and his foundational contributions to the field of VECSEL lasers. emerging semiconductor materials and related technologies for gain mirror fabrication. To this end we could mention the development of straincompensated GaInAs/GaAs gain mirrors, development of GaInNAsSb/
GaAs-based gain mirrors with wavelength coverage between 1.1 µ m and 1.5
µ m, development of InAs/GaAs QD-based mirrors, use of wafer bonding technology, development of GaInAsSb/GaSb gain mirrors with emission beyond 2 µ m, or the emergence of InGaN/GaN-based VECSELs with emission at blue wavelengths. On the other hand, intracavity frequency doubling has enabled attaining power levels above 20W for wavelengths covering green, yellow, and orange bands. Major developments have been also made concerning generation of UV wavelengths as well as of
THz radiation. Moreover, cavity stabilization techniques combined with wavelength selective elements, have enabled attaining high-power outputs with a narrow-linewidth, and eventually continuously tuneable, which are instrumental features for spectroscopic applications.
The paper is focused on reviewing the major progress in continuous-wave
VECSELs. Emphasis is put on advances concerning power scaling and related thermal management techniques, and wavelength coverage. The progress will be discussed in connection with established and emerging applications that have fostered the tremendous progress experienced by
VECSEL technology during the last decade.
9734-2, Session 1
(Invited
Paper)
John G . McInerney, Univ . College Cork (Ireland)
The NECSEL is a VECSEL based on an electrically pumped semiconductor gain element with integrated Bragg gratings and a single-ended external compound cavity for mode selection and coherence enhancement. Initially designed for 980 nm operation, it produced multi-watt quasi-CW outputs with M2 < 1.2. A hybrid integrated version produced ~0.1 W CW in a TOstyle can. Mode-locked versions of the full NECSEL produced ~1 ps pulses transform limited with ~0.1 kW peak powers. Subsequent designs used intracavity frequency doubling, initially using bulk nonlinear crystals for blue emission, later migrating to quasi-phasematched PPLN arrays as these became available.
9734-3, Session 1
(Invited Paper)
Mircea Guina, Tampere Univ . of Technology (Finland)
The development of continuous-wave VECSELs has reached a maturity level that enables deployment of a wide range of applications in spectroscopy, pumping and cooling of solid-state media, biophotonics, or laser projection, just to mention a few. During the past years, the most diverse and intense developments have aimed at reaching new wavelengths by deploying
9734-4, Session 1
(Invited Paper)
Ursula Keller, ETH Zürich (Switzerland)
Aram Mooradian made pioneering contributions for a novel type of laser that has bridged the gap between semiconductor lasers and solidstate lasers. The high-power optically pumped vertical-external-cavity surface-emitting laser (VECSEL) combines the best of both worlds: the semiconductor gain medium allows for flexible choice of emission wavelength via bandgap engineering and good pump efficiency is obtained from fairly low-cost, low-beam-quality high-power diode laser bars into a near-diffraction-limited output beam. The VECSEL is part of the family of VCSELs which are the most frequently manufactured semiconductor lasers today. In contrast to a VCSEL a VECSEL has an external cavity and is either optically or electrically pumped. VECSELs also have been passively modelocked using a semiconductor saturable absorber mirror (SESAM).
The MIXSEL (i.e. modelocked integrated external-cavity surface emitting laser) combines the gain of VECSELs with the saturable absorber of a
(SESAM) in a single semiconductor device. Hence, self-starting and stable passive modelocking is obtained in a simple straight cavity formed by the semiconductor chip and a curved output coupler. The VECSEL and MIXSEL are part of the family of ultrafast semiconductor disk lasers which rapidly advanced over the last decades. The strong interest from industry for inexpensive, compact and reliable ultrafast laser sources in the picosecond and femtosecond domain has driven this technology towards first commercial products. Frequency metrology and biomedical applications would benefit from sub-200 femtosecond pulse durations with peak powers in the kilowatt range. This talk is a tribute to Aram Moradian and will give an overview of the recent advances.
9734-5, Session 2
(Invited Paper)
Sandro M . Link, Mario Mangold, Matthias Golling,
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Conference 9734: Vertical External Cavity Surface
Emitting Lasers (VECSELs) VI
Alexander Klenner, Ursula Keller, ETH Zürich (Switzerland)
One passively modelocked laser can simultaneously generate two gigahertz, orthogonally polarized and collinear frequency combs with slightly different but adjustable pulse repetition rates. This is successfully demonstrated for both, a semiconductor disk laser (SDL), also referred to as vertical external cavity surface emitting laser (VECSEL) and a solid-state Nd:YAG laser, each pumped with the same multimode diode array pump laser. This laser uses an intracavity birefringent crystal, which splits the one cavity beam into two spatially separated and orthogonally polarized beams. The SDL is a modelocked integrated external-cavity surface emitting laser (MIXSEL) that combines the saturable absorber of a SESAM with the gain of a VECSEL in a single semiconductor structure and enables dual-output operation in a simple linear straight cavity. The demonstration of dual-polarized output with the Nd:YAG laser extends this technique to ion-doped solid-state laser technologies. Such compact and cost-efficient dual-comb sources are interesting for spectroscopic applications. The microwave frequency comb, generated by the optical beat of the two orthogonal pulse trains, can be used to down-convert the terahertz optical frequencies into the electronically accessible microwave regime. The comb is detected simply by superimposing the two beams in the same polarization on a photodetector.
Using a second birefringent crystal of same length but with the optical axis rotated by 90° results in two pulse trains with the same pulse repetition frequency, allowing to directly detect and characterize the relative carrier envelope offset (CEO) frequency dynamics. The stabilization and noise characterization of the dual comb laser will be presented.
Andrew P . Turnbull, Univ . of Southampton (United
Kingdom); Markus Polanik, Univ . Ulm (Germany); Edward
A . Shaw, Theo Chen Sverre, Univ . of Southampton (United
Kingdom); Peter Unger, Univ . Ulm (Germany); Anne C .
Tropper, Univ . of Southampton (United Kingdom)
We present a VECSEL based on a gain sample design which utilizes only a single layer dielectric Al2O3-coating for dispersion management. The calculated GDD, over a 30-nm range around the lasing wavelength of 1035 nm, was -38 ± 33 fs2. The gain structure generated in combination with a surface-recombination SESAM pulse durations down to 193 fs with an average power of 400 mW at 1.6 GHz with an incident pump power of 30 W, setting a new peak power record for sub-200 fs mode-locked VECSELs.
The obtained sech2-pulses were not transform-limited and had a timebandwidth product of up to 0.64. A subsequent FROG analysis of the pulse train revealed significant higher-order chirp characteristics. In order to investigate where the higher-order dispersion components arise from pulse trains generated by various VECSELs, with similar gain chip layer designs that have only small differences, have been investigated using the FROG analysis.
An optimized gain chip design for higher-order dispersion management could reduce the time bandwidth product and thus further push the pulse duration towards the 100-fs mark, at which point VECSELs become an interesting source for applications such as direct GHz frequency comb generation.
9734-6, Session 2
Cesare G . E . Alfieri, Dominik Waldburger, Sandro M .
Link, Emilio Gini, Matthias Golling, Bauke W . Tilma, Mario
Mangold, Ursula Keller, ETH Zürich (Switzerland)
A modelocked integrated external cavity surface emitting laser (MIXSEL) is the most simple and compact type of ultrafast semiconductor disk laser, as it is operated in a straight linear cavity. High-power ultrafast MIXSELs offer highest repetition rate flexibility together with high performance in terms of pulse duration, average and peak power and are thus ideal candidates for applications in the fields of metrology and imaging.
Here, we present the first sub-300-fs MIXSEL, fabricated by a regrowth scheme in MOVPE and MBE. The structure includes a lower field enhancement in the gain and an improved dispersion. We obtained 235 mW of average output power at a wavelength of 1044 nm and a repetition rate of 3.35 GHz. A pulse duration of 253 fs was retrieved from frequencyresolved optical gating measurements. The resulting 240-W peak power is the highest from a MIXSEL thus far. At 10 GHz repetition rate, we obtained a pulse duration of 279 fs and 310 mW of average output power.
In addition, we developed MOVPE-grown saturable absorbers with fast recovery dynamics that were subsequently implemented in the first entirely
MOVPE-grown MIXSEL. This MIXSEL delivered 1.56 W of average output power with 15.4 ps pulses at a repetition rate of 3.66 GHz. In a different configuration pulses as short as 2.6 ps with 301 mW of average output power at 5.84 GHz repetition rate were obtained. MOVPE-growth not only reduces growth complexity and losses introduced by regrowth of a MIXSEL, but also makes the technology more accessible for the optoelectronics industry.
9734-8, Session 2
Dominik Waldburger, Cesare G . E . Alfieri, Sandro M . Link,
Emilio Gini, Matthias Golling, Mario Mangold, Bauke W .
Tilma, Ursula Keller, ETH Zürich (Switzerland)
Ultrafast, optically pumped, vertical external-cavity surface-emitting lasers
(VECSELs) are excellent sources for industrial and scientific applications that benefit from compact semiconductor based high-performance lasers with gigahertz pulse repetition rates and excellent beam quality. Applications such as self-referenced frequency combs and multi-photon imaging could benefit from sub 150-fs pulse durations combined with high pulse peak power.
Here, we present our recent progress in sub-150-fs semiconductor saturable absorber mirror (SESAM) modelocked VECSELs. In order to obtain the short pulse durations, we utilized precise dispersion engineering and an active region designed for broadband gain. Furthermore, a low and flat average field enhancement of the active InGaAs quantum wells of ≈ 0.5 (normalized to 4 outside the structure) ensures high gain saturation fluences. In combination with a SESAM with fast recovery dynamics, 128-fs pulses with
303 W of pulse peak power were obtained. The average output power was 80 mW with a pulse repetition rate of 1.8 GHz at a central wavelength of 1033 nm. In a similar configuration 147-fs pulses with 328 W of pulse peak power have been achieved. Both laser configurations operated in a fundamental transverse mode with an M2 value of <1.05 in both orthogonal directions. Those results mark the shortest pulse durations of any ultrafast
VECSELs in the >50-mW average power regime.
With full characterization of the gain and saturable absorber parameters, we can identify current limitations of our ultrafast VECSELs and present guidelines to maintain the short pulse durations while scaling the technology to even higher pulse peak power.
9734-7, Session 2
Christopher R . Head, Univ . of Southampton (United
Kingdom); Alexander Hein, Univ . of Ulm (Germany);
116 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9734: Vertical External Cavity Surface
Emitting Lasers (VECSELs) VI
9734-9, Session 2
(Invited
Paper)
Loyd J . McKnight, Peter J . Schlosser, Alexander A .
Lagatsky, Martin D . Dawson, John-Mark Hopkins,
Fraunhofer Ctr . for Applied Photonics (United Kingdom)
Modelocked semiconductor disk lasers (SDLs) offer a low-cost, compact and versatile solution for nonlinear microscopy, however, the desirable repetition rate of 80-100 MHz is hard to achieve without the short carrier lifetime in the semiconductor gain chip causing multiple pulsing effects or a drop in efficiency. We have developed a number of novel multi-pass cavities that solve this problem by passing the intracavity beam through the optically pumped gain region multiple times per round trip of the cavity. This has the effect of reducing the time between intracavity pulses hitting the gain region whilst ensuring a clean and efficient low repetition rate output. Using
8 passes of the gain region per round trip we achieved a repetition rate of
86 MHz offering output powers above 120 mW and pulse durations of 2.2 ps. This represents a peak power greater than 500 W whilst maintaining gain and semiconductor saturable absorber mirror (SESAM) chips at room temperature. A number of cavities will be presented including those with repetition rates of 112 MHz and 230 MHz with similar power levels and pulse durations. For this work we designed antiresonant SDL gain wafers at a wavelength of ~955 nm, capable of efficiently exciting green fluorescent protein in a two-photon process, and a surface-recombination SESAM that offers a fast relaxation time. Details of the novel cavities and the gain and SESAM structures will be presented including a comprehensive characterization of the clean modelocked operating regime.
9734-10, Session 3
(Invited Paper)
Marcel Rattunde, Peter Holl, Steffen Adler, Fraunhofer-
Institut für Angewandte Festkörperphysik (Germany);
Sebastian Kaspar, AIM INFRAROT-MODULE GmbH
(Germany); Andreas Bächle, Elke Diwo, Rolf Aidam,
Wolfgang Bronner, Joachim Wagner, Fraunhofer-Institut für Angewandte Festkörperphysik (Germany)
Narrow-linewidth, tunable laser sources in the 2 – 3 µ m wavelength range are of special interest for a range of applications such as gas analysis, remote sensing, LIDAR, optical free-space communication, laser seeding as well as for fundamental research like quantum optical experiments.
Vertical external cavity surface emitting lasers (VECSEL) based on the
(AlGaIn)(AsSb) materials system are ideally suited to serve these needs.
High-efficient, high-power gain mirrors are available [1,2] and by including wavelength-selective elements in the laser cavity, narrow-linewidth singlefrequency emission and wavelength tunability can be achieved [3]. Without active stabilization, the emission-linewidth of the VECSEL can be well below
100 kHz and by scaling the pump- and mode-spot to larger diameters, over
2W (3W) single-frequency emission could be achieved at 2.0 µ m and 20°C
(3°C) heatsink temperature [4].
In this presentation recent advances concerning these single-frequency sources will be reviewed with special emphasis on the different mounting and heat extraction technologies for the VECSEL chip and their influence on the spectral properties and the VECSEL efficiency. Further on, alternative approaches for wavelength control (such as self-seeding) will be presented and discussed, together with a requirement analysis for the different applications.
References
[1] P. Holl et al, IEEE J Sel Top Quantum Electron. 21 (6), (2015).
[2] J. Paajaste et al., J. Cryst. Growth 311, 1917 (2009)
[3] O. Ochotnikov, Ed., “Semiconductor Disk Laser”, Wiley-VCH, 2010
[4] S.Kaspar et al., IEEE JSTQE 19, 1501908 (2013)
9734-11, Session 3
Stephane Denet, Innoptics SAS (France); Baptiste Chomet,
Univ . Montpellier 2 (France); Vincent Lecocq, Laurence
Ferrières, Innoptics SAS (France); Mikhaël Myara, Laurent
Cerutti, Univ . Montpellier 2 (France); Isabelle Sagnes, Lab . de Photonique et de Nanostructures (France); Arnaud
Garnache, Univ . Montpellier 2 (France)
Applications such as spectroscopy, lidar, or velocimetry require highly coherent tunable laser sources. The Vertical External Cavity Surface Emitting
Laser (VECSEL) III-V semiconductor technology is a good candidate, with promising lab results already demonstrated.
Inside a research group gathering expertise in chip design and epitaxy, laser cavity design, compact and robust laser packaging and noise measurements, we are currently developing a family of VECSEL-based modules, in the 0.8-1.1 µ m (GaAs-based) and 2-2.5 µ m (Sb-based) spectral windows, with future developments at 1.5 µ m.
We are presenting here tunable single frequency modules at 1 µ m and 2.3
µ m. Featuring a ? VCSEL chip being part of a sub-mm laser cavity, the modules also comprise a compact system for optical pumping, means for laser temperature monitoring, and a monitoring photodiode.
At 1 µ m we demonstrate high power (> 60mW), high coherence, low divergence diffraction limited TEM00 beam, high spectral purity (SMSR
>55dB) and linear polarization (50dB PER), while at 2.3 µ m broadband continuous tuning (> 7nm) and overall tunability of 80 nm are achieved.
Those performances can be reached thanks to a high finesse cavity associated with ideal homogeneous QW gain behavior. In addition, the design without any intracavity element offers a robust single frequency regime with a good long term wavelength stability.
Ongoing developments intend to enhance the main specifications for each application (tunability at 2.3 µ m and low noise at 1 µ m). Dedicated control electronics are also under development in order to improve laser stability.
9734-12, Session 3
(Invited Paper)
Fabien Bretenaker, Lab . Aimé Cotton (France) and Ecole
Normale Supérieure de Cachan (France)
Optical generation of tunable high-purity radio-frequency (RF) signals is essential for the future optoelectronic communication systems such as broadband mobile systems [1], satellite networks [2], long-range transmission of high purity radio-frequency (RF) references, etc. One way to generate such low noise optically carried RF signals is to build two-frequency lasers. In this case, the beatnote between the two optical frequencies provides the desired RF signal. This approach has been applied in the case of solid-state lasers [3,4]. But, in this case, the excess noise induced by the laser relaxation oscillation noise is detrimental to the spectral purity of the carried RF signal. However, recently, optically pumped Vertical
External Cavity Surface Emitting Lasers (VECSELs) have been shown to obey the class-A regime, i. e., to exhibit no relaxation oscillations. These
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Conference 9734: Vertical External Cavity Surface
Emitting Lasers (VECSELs) VI lasers are thus capable of emitting a single-frequency with an ultralow intensity noise [5-7]. Our aim here is to show how such VECSELs can be made to oscillate in dual-frequency regime [8,9], and to report our recent efforts to elucidate the physical mechanisms that give rise to the phase noise observed in the generated RF signal [10,11,12].
1. D. C. Ni, H. R. Fetterman, and W. Chew, IEEE Trans. Microwave Theory
Technol. 38, 608 (1990).
2. U. Gliese, E. L. Christensen, and K. E. Stubkjaer, J. Lightwave Technol. 9,
779 (1991).
3. M. Alouini, B. Benazet, M. Vallet, M. Brunel, P. Di Bin, F. Bretenaker, A. Le
Floch, and P. Thony, IEEE Photon. Tech. Lett. 13, 367 (2001).
4. G. Pillet, L. Morvan, M. Brunel, F. Bretenaker, D. Dolfi, M. Vallet, J.-P.
Huignard, and A. Le Floch, J. Lightwave Technol. 26, 2764 (2008).
5. G. Baili, M. Alouini, D. Dolfi, F. Bretenaker, I. Sagnes, and A. Garnache, Opt.
Lett. 32, 650 (2007).
6. G. Baili, F. Bretenaker, M. Alouini, L. Morvan, D. Dolfi, and I. Sagnes, J.
Lightwave Technol. 26, 952 (2008).
7. G. Baili, L. Morvan, G. Pillet, S. Bouchoule, Z. Zhao, J.-L. Oudar, L. Ménager,
S. Formont, F. Van Dijck, M. Faugeron, M. Alouini, F. Bretenaker, and D. Dolfi,
J. Lightwave Technol 32, 3489 (2014).
8. G. Baili, L. Morvan, M. Alouini, D. Dolfi, F. Bretenaker, I. Sagnes, and A.
Garnache, Opt. Lett. 34, 3421 (2009).
9. F.A. Camargo, J. Barrientos, G. Baili, L. Morvan, D. Dolfi, D. Holleville, S.
Guerandel, I. Sagnes, P. Georges, and G. Lucas-Leclin, Opt. Lett. 34, 3421
(2009).
10. S. De, V. Pal, A. El Amili, G. Pillet, G. Baili, M. Alouini, I. Sagnes, R. Ghosh, and F. Bretenaker, Opt. Expr. 21, 2538 (2013).
11. S. De, A. El Amili, I. Fsaifes, G. Pillet, G. Baili, F. Goldfarb, M. Alouini, I.
Sagnes, and F. Bretenaker, J. Lightwave Technol. 32, 1307 (2014).
12. S. De, G. Baili, S. Bouchoule, M. Alouini, and F. Bretenaker, Phys. Rev. A 91,
053828 (2015).
emitting gain chip. The gain chip had ten 7-nm-thick GaInAs quantum wells, with an indium mole fraction of 35%. The accumulation of net strain was eliminated by using GaAsP strain compensation layers. An intra-cavity birefringent filter and an etalon were used to achieve single frequency operation and wavelength tuning. The laser line-width was measured to be less than 140 kHz using a heterodyne measurement with a narrow linewidth fiber laser. The laser was stabilized against long term drifts using a frequency offset lock between the VECSEL and the fiber laser (which was stabilized to a Doppler free transition in molecular Iodine) or a direct lock to an Iodine transition.
Second harmonic generation in a waveguide doubler produced up to
350mW at 559nm which was subsequently frequency doubled in an external build up cavity to produce up to 22mW in the UV at 280nm. The system was used to Doppler-cool a single 25 Mg ion in an RF Paul trap on the S1/2 |3,3>->P3/2 |4,4> transition. The slightly saturated and residually
Doppler-broadened line width of this transition was measured to be 45MHz.
The laser was also tuned to 1121nm to perform high resolution spectroscopy of the S1/2 |2,2>->P1/2 |3,3> transition. This work demonstrates the versatility of VECSELs in high precision spectroscopy of trapped atoms and provides a scalable laser source for the development of ion trap quantum information processors.
9734-14, Session 4
(Invited
Paper)
Arnaud Garnache, Mohamed Seghilani, Romain Paquet,
Mohamed Sallhai, Baptiste Chomet, Mikhael Myara,
Stephane Blin, Univ . Montpellier 2 (France); Isabelle
Sagnes, Gregoire Beaudoin, Luc Legratiet, LPN CNRS
(France); Philippe Lalanne, LP2N IOGS (France)
9734-13, Session 3
Shaun C . Burd, National Institute of Standards and
Technology (United States) and Univ . of Colorado at
Boulder (United States); Tomi Leinonen, Jussi-Pekka
Penttinen, Optoelectronics Research Ctr . (Finland); David
T . Allcock, National Institute of Standards and Technology
(United States); Raghavendra Srinivas, National Institute of Standards and Technology (United States) and Univ . of Colorado at Boulder (United States); Daniel H . Slichter,
Andrew C . Wilson, Dietrich Leibfried, National Institute of Standards and Technology (United States); Mircea
Guina, Optoelectronics Research Ctr . (Finland); David J .
Wineland, National Institute of Standards and Technology
(United States) and Univ . of Colorado at Boulder (United
States)
The recent advances in the field of quantum information processing have paved the way for high performance computing and high precision measurements of physical parameters. These developments rely on laser cooling of atoms and ions using narrow-linewidth, resonantly tuned lasers.
Vertical-external-cavity surface-emitting laser (VECSEL) system device geometry enables the combination of single-frequency operation and good beam quality with the wavelength versatility of semiconductors, which are advantageous features for these applications. Here we report on laser cooling and high precision spectroscopy of trapped Magnesium ions using a frequency quadrupled VECSEL.
Light at 1118nm was generated using an I-cavity VECSEL with a bottom
Since years, the VeCSEL concept is pointed out as a technology of choice for beyond-state-of-the-art laser light sources, demonstrating wavelength flexibility, high power, high spatial and temporal coherence, linear polarization state, CW or ultra-short pulsed operation, compactness and functionalities. The targeted coherent state is typically the gaussian
TEM00, single frequency, linearly polarized light state. In this work, we take advantage of the VeCSEL technology for generation of new kinds of coherent states, thanks to insertion of intracavity functions based on flat photonics. These new coherent states target many applications including optical tweezers, telecommunications, fundamental physics, sensors… A first part of this work aims at demonstrating new spatial domain coherent state.
We developed a semiconductor flat photonic technology for intracavity transverse phase and intensity control. Intensity control is obtained thanks to sub-wavelength metallic masks. For phase control, we developed an ultra-low loss metamaterial technology. This technological development permitted generation and control of high coherence single or dual high order Laguerre-Gauss mode, VORTEX or Hermite-Gauss mode, preserving the spatial and temporal coherence properties of usual TEM00 VeCSELs. It paves the way for the generation of new coherent beams and functionalities: wavelength filtering, dual frequency for THz source. In a second part, we explore new time domain coherent state: owing to a high gain semiconductor chip design and insertion of an intracavity acousto-opticfrequency-shifter, we demonstrated and studied the first semiconductorbased low noise broadband modeless laser, with a 300 GHz band and a coherence length of 4km.
118 SPIE Photonics West 2016 · www.spie.org/pw
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9734-15, Session 4
Conference 9734: Vertical External Cavity Surface
Emitting Lasers (VECSELs) VI
Luyao Xu, Christopher A . Curwen, Philip W . C . Hon, Tatsuo
Itoh, Benjamin S . Williams, Univ . of California, Los Angeles
(United States)
Vertical-external-cavity surface-emitting lasers (VECSELs) have been successfully used in the visible and near-infrared to achieve high output power with excellent Gaussian beam quality. However, the concept of
VECSEL has been impossible to implement for quantum-cascade (QC) lasers, since the optical gain is based on intersubband transitions of electrons, which only interact with the electric field polarized perpendicular to the quantum wells plane according to the “intersubband selection rule”.
In this work we demonstrated a terahertz (THz) quantum cascade external cavity laser, which is also the first VECSEL in the terahertz regime. The enabling component for the QC-VECSEL is an amplifying metasurface reflector composed of a sparse array of metallic sub-cavities, which allows the normally incident radiation to interact with the electrically pumped QC gain medium. The QC-VECSEL is implemented in a plano-plano Fabry-Perot cavity, with a wire-grid polarizer as its output coupler. A beam of 4.3° ? 5.1°
FWHM divergence and a near-Gaussian profile is observed with an output power > 5 mW. THz QC-lasers have often been characterized by poor beam quality due to their sub-wavelength metallic waveguides. The symmetry and circularity of the beam are further improved by placing an aperture into the cavity. Our work on THz QC-VECSEL initiates a new approach towards achieving scalable output power in combination with a diffraction-limited beam pattern for THz QC-lasers. Furthermore, the intra-cavity access of the
VECSEL gives tremendous versatility to QC-lasers, such as the ability for mode engineering.
9734-17, Session 4
Zhou Yang, Alexander R . Albrecht, The Univ . of New
Mexico (United States); Jeffrey G . Cederberg, Sandia
National Labs . (United States); Shawn Hackett, The Univ . of New Mexico (United States) and Air Force Research
Lab . (United States); Mansoor Sheik-Bahae, The Univ . of
New Mexico (United States)
Semiconductor disk lasers (SDLs) have gained lots of attention due to their wavelength flexibility and high output powers. With the external cavity configuration, they are superior to edge-emitting semiconductor lasers for applications requiring intra-cavity optical elements, like non-linear crystals for frequency conversion or saturable absorbers for mode-locking.
Theoretically, SDL is power scalable but the low thermal conductivity semiconductor DBR impedes the heat removal process. For DBR-free SDLs, a multi-quantum-well (MQW) active region is grown on a substrate with a sacrificial layer. Then the MQW is lifted off and van der Waals bonded onto transparent high thermal conductivity substrates, such as diamond. Without a need for lattice-matched semiconductor distributed Bragg reflectors
(DBRs), these SDLs can be realized in more material systems and cover a wider wavelength range. Also, the tuning range would no longer be limited by the high-reflection bandwidth of the DBR, but instead by the broader high reflection band of the external dielectric mirrors. Based on thermal analysis, the DBR-free geometry with diamond heatspreaders on both sides of the active region has advantages in thermal management over traditional
SDLs. For an InGaAs MQW sample bonded to one single-crystalline CVD diamond, preliminary experiments show a record 78 nm tuning range centered at 1150nm. The CW output power at 1150 nm was 2.5 W. For another active region, 4 W output power (limited by the available pump power) is collected at 1040 nm. Currently efforts are underway to improve laser performance and power scaling by mitigating intracavity losses.
9734-16, Session 4
Christoph Möller, Christian Berger, Christian Fuchs,
Philipps-Univ . Marburg (Germany); Antje Ruiz Perez, NAsP
III/V GmbH (Germany); Stephan W . Koch, Philipps-Univ .
Marburg (Germany); Jörg Hader, Jerome V . Moloney,
Nonlinear Control Strategies (United States); Wolfgang
Stolz, Philipps-Univ . Marburg (Germany) and NAsP III/V
GmbH (Germany)
9734-18, Session 5
(Invited
Paper)
Adrian H . Quarterman, Univ . of Dundee (United Kingdom);
Edward E . Shaw, Univ . of Southampton (United Kingdom);
Keith G . Wilcox, Univ . of Dundee (United Kingdom) Since the invention of VECSELs, their great spectral coverage has been demonstrated and emission wavelengths in the range from UV to almost
MIR have been achieved. However, in the infrared regime the laser performance is affected by Auger losses which become significant at large quantum defects. In order to reduce the Auger losses and to develop more efficient devices in the IR, type-II aligned QWs have been suggested as alternative gain medium for semiconductor lasers.
We present the first room temperature VECSEL containing type-II aligned quantum wells arranged as resonant periodic gain. The quantum wells consist of (GaIn)As/Ga(AsSb)/(GaIn)As heterostructures. The structure was grown bottom-up on GaAs substrate and flip-chip bonded onto a diamond heat spreader. The device, pumped at 808 nm, emits >1 W of cw output power at an emission wavelength of 1.2 ?m. A detailed study of the device is performed in order to investigate the potential of such novel type-II gain media for future applications. These investigations include the determination of the power and temperature dependent shift rates.
The gain temperatures at laser threshold and at maximum output power are determined. Furthermore, edge photoluminescence and reflectivity measurements are performed in order to accurately determine the detuning.
These experimental results are compared with fully microscopic simulations.
In recent years there have been several reports describing self-modelocking
(SML) in vertical-external-cavity surface-emitting lasers (VECSELs). Some of these reports have suggested that the behaviour that has been observed results from nonlinear lensing in the VECSEL gain sample in a manner analogous to Kerr lens modelocking in solid state lasers. However to date none of the groups that have reported SML in VECSELs have performed measurements to ascertain whether nonlinear lensing occurs in the gain sample. Measurements of nonlinear lenses in VECSEL gain samples are therefore of value not only in order to understand the behaviour observed in the reports of SML, but also as a potentially crucial design tool for any mode-locked VECSEL, regardless of the modelocking method used.
In a previous publication [1] we described measurements which demonstrated that a defocussing nonlinear lens was present in an unpumped VECSEL gain sample, and that the inverse focal length of the lens increased with pump power, to the point of becoming a focussing lens for sufficiently high pump powers. Unfortunately, by necessity this measurement was performed using a probe laser which was not resonant with the quantum wells in the sample, meaning that the values measured may well be different from those experienced under operating conditions in a VECSEL. This paper will describe a more complete characterisation of
VECSEL gain sample nonlinear lensing with a probe laser whose wavelength
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Conference 9734: Vertical External Cavity Surface
Emitting Lasers (VECSELs) VI is resonant with the gain sample quantum wells.
[1] Quarterman et al. Applied Physics Letters, 106, 011105 (2015).
9734-19, Session 5
Caleb Baker, Maik Scheller, Hwang-Jye Yang, College of
Optical Sciences, The Univ . of Arizona (United States);
Stephan W . Koch, College of Optical Sciences, The Univ . of Arizona (United States) and Philipps-Univ . Marburg
(Germany); Ronald J . Jones, Jerome V . Moloney, College of Optical Sciences, The Univ . of Arizona (United States);
Antje Ruiz Perez, Wolfgang Stolz, Philipps-Univ . Marburg
(Germany); Sadhvikas Addamane, Ganesh Balakrishnan,
The Univ . of New Mexico (United States) mode-locking regimes, thought to arise from a non-linear lens in the
VECSEL gain structure.
Recently, the first measurement of the non-linear lens in a gain chip showed that the power and sign of the lens depends sensitively on the pumping conditions. The photon energy of the probe laser used in these measurements was less than the band gap energy of the quantum wells.
Third-order refractive indices in semiconductors, however, are known to vary rapidly with the photon energy around the band gap. Here we present reflection z-scan measurements that probe the quantum well structure slightly above the band gap, in resonance with the typical operating wavelength of the laser. The strength of the non-linear lens is experimentally determined at pump densities and with pulse fluences approaching values typical for SESAM mode-locked VECSELs.
9734-21, Session 5
(Invited Paper)
Arash Rahimi-Iman, Mahmoud Gaafar, Christoph Möller,
Max Vaupel, Fan Zhang, Dalia Al-Nakdali, Philipps-Univ .
Marburg (Germany); Ksenia A . Fedorova, Aston Univ .
(United Kingdom); Wolfgang Stolz, Philipps-Univ . Marburg
(Germany) and NAsP III/V GmbH (Germany); Edik U .
Rafailov, Aston Univ . (United Kingdom); Martin Koch,
Philipps-Univ . Marburg (Germany)
As Vertical External-Cavity Surface-Emitting Lasers (VECSELs) become increasingly interesting candidates among the ultrafast class of modelocked sources, better understanding of their carrier dynamics on ultrafast timescales is necessary. To this end, we present a comprehensive characterization of semiconductor gain and absorber devices utilizing novel measurement techniques to supplement traditional pump and probe measurements.
For our studies, we utilize a mode-locked, amplified, ytterbium fiber laser emitting 12nJ pulses with a bandwidth centered at 1040nm and a pulse duration of 120fs as probe laser source. The pulses are spectrally broadened in a single-mode fiber to cover the wavelength range between 940nm to
1100nm. The resulting pulses are compressed using a pulse shaper to a pulse duration of 20fs. The pulse shaper is also used to spectrally resolve measurements by creating 100fs pulses with varying center wavelengths to interact with the samples.
Time resolution in the few femtosecond range results from traditional pump and probe measurements performed on VECSEL and SESAM samples with different designs. In-situ characterizations based on an asynchronous optical sampling technique of VECSEL samples mode-locked in the sub-500fs regime reveal additional long time recoveries of the gain present in real lasing condition.
Our results indicate that multiple carrier relaxation mechanisms exists ranging in timescale from hundreds of femtoseconds to pico- and nanosecond regimes which affect the stability of mode-locking states as well as the pulse duration. Our study can contribute to development design strategies to optimize the gain chips and absorbers for further performance improvements.
Within the last 15 years, a new class of pulsed lasers emerged which proved capable of generating ultrashort pulses. Semiconductor disk lasers, also referred to as vertical-external-cavity surface-emitting lasers (VECSELs), have become promising sources of fs-pulsed laser light which indeed can serve many applications, such as ultrafast spectroscopy, metrology, multiphoton microscopy, or material processing. Moreover, the externalcavity design of such lasers allow for versatility, compactness and beam quality – aspects which are all beneficial to the employment of VECSELs.
However, with respect to a practical use, also robustness, flexibility and costefficiency play a role, which can be addressed via an approach referred to as saturable-absorber-free mode-locking, or self-mode-locking (SML).
Much work has been performed in the field of saturable-absorber-based pulsed VECSELs by the community to provide ever shorter pulses using resonator-integrated or even chip-integrated semiconductor saturableabsorber mirrors (SESAMs), which have demonstrated an excellent performance of pulsed VECSELs with pulse durations in the range of 100 fs to picoseconds. Nevertheless, SML VECSELs can circumvent limitations naturally imposed on the device’s performance by SESAMs, which are costly and have to be individually designed for a certain operation wavelength.
Here, we highlight recent achievements in the field of self-mode-locking of VECSELs with quantum-well as well as quantum-dot based gain media.
Furthermore, assuming a nonlinear lensing effect to play a significant role for SML operation, we have studied the influence of a few VECSEL parameters on SML, such as power densities and cavity geometries, in the context of recent considerations of a nonlinear refractive index.
9734-20, Session 5
Edward A . Shaw, Univ . of Southampton (United Kingdom);
Adrian Quarterman, Univ . of Dundee (United Kingdom);
Andrew P . Turnbull, Theo Chen Sverre, Christopher R .
Head, Anne C . Tropper, Univ . of Southampton (United
Kingdom); Keith G . Wilcox, Univ . of Dundee (United
Kingdom)
Recent advances in thermal management of VECSEL gain structures using
‘flip-chip’ bonding have enabled the use of much higher pump densities than were previously possible. This has led to the achievement of record high output powers for both continuous-wave and mode-locked VECSELs.
High pump densities have been associated with the observation of self-
9734-22, Session 6
(Invited Paper)
David Paboeuf, Brynmor E . Jones, Julio M . Rodríguez
García, Peter J . Schlosser, Univ . of Strathclyde (United
Kingdom); Dariusz Swierad, Joshua Hughes, Ole Kock,
Lyndsie Smith, Kai Bongs, Yeshpal Singh, The Univ . of
Birmingham (United Kingdom); Stefano Origlia, Stephan
Schiller, Heinrich-Heine-Univ . Düsseldorf (Germany);
120 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9734: Vertical External Cavity Surface
Emitting Lasers (VECSELs) VI
Jennifer E . Hastie, Univ . of Strathclyde (United Kingdom)
Optically-pumped semiconductor disk lasers (SDLs) have been shown over the past decade to possess all the qualities required for quantum technology applications. Indeed the very specific dynamics of these lasers make them perfect candidates to achieve low intensity noise and sub-Hz linewidth. Moreover, bandgap engineering and nonlinear conversion allow very broad spectral coverage from the ultraviolet to the mid-infrared, while the external cavity provides an excellent beam quality.
At the University of Strathclyde, we have been working for several years on
GaInP based SDLs emitting in the 670-690 nm spectral band. Powers up to 1
W and single frequency emission have been achieved with these structures.
By locking to a reference cavity, a relative frequency noise of 5 kHz (over 1 s) has been achieved, demonstrating the suitability of these sources for high coherence emission. This high coherence can be transferred to wavelengths in the UV by means of non-linear conversion. Such high coherence UV sources could find applications in UV photolithography or atmospheric spectroscopy.
We recently started to develop laser sources suitable for quantum technologies, in particular the laser cooling of Strontium atoms within optical clocks. A power above 100 mW and relative frequency stability of
5 kHz has been achieved. This narrow linewidth laser at 689 nm has been moved to the University of Birmingham and used to trap millions of Sr atoms cooling down to ~170?K. This establishes the narrow linewidth and high spectral purity of the laser. Results and characterisation carried out will be provided.
9734-23, Session 6
Daniele C . Parrotta, Riccardo Casula, Univ . of Strathclyde
(United Kingdom); Jussi-Pekka Penttinen, Tomi Leinonen,
Tampere Univ . of Technology (Finland); Alan J . Kemp, Univ . of Strathclyde (United Kingdom); Mircea Guina, Tampere
Univ . of Technology (Finland); Jennifer E . Hastie, Univ . of
Strathclyde (United Kingdom)
9734-25, Session 6
Esa J . Saarinen, Jari Lyytikäinen, Sanna Ranta, Antti
Rantamäki, Antti Saarela, Tampere Univ . of Technology
(Finland); Alexei Sirbu, Vladimir Iakovlev, Eli Kapon, Ecole
Polytechnique Fédérale de Lausanne (Switzerland); Oleg
G . Okhotnikov, Tampere Univ . of Technology (Finland)
1.5 W of output power was obtained in the challenging wavelength range between 700 and 800 nm by frequency doubling a wafer-fused 1.49-?m semiconductor disk laser (SDL). The SDL was pumped with low-cost 980nm diodes. The demonstrated scheme for accessing wavelengths in the vicinity of 750 nm is a viable alternative to bulky and expensive Ti:Sapphire and Alexandrite lasers that require pumping with visible light. Moreover, the performance of diodes emitting directly at around 750 nm is limited by the lack of appropriate compound semiconductors. The gain element of the
SDL comprised an InP-based resonant periodic gain section and a GaAsbased distributed Bragg reflector assembled in contact with a transparent intracavity diamond heat spreader. A 5-mm long bismuth borate crystal was used for doubling the frequency in a Z-shaped cavity where the gain element was placed as a folding mirror. A total optical-to-optical efficiency of 8.3 % was achieved. The SDL was tunable from 720 to 764 nm with an intracavity birefringent plate. Full width at half maximum (FWHM) of the tuning curve was about 30 nm, centered at 745 nm. The beam quality parameter M2 of the laser remained below 1.5 at all power levels. The laser is attractive for biomedical applications such as photodynamic therapy and fluorescence imaging that benefit from the low absorption of light in tissue in this spectral range.
9734-26, Session 7
(Invited Paper)
Yanbo Bai, Jeffrey A . Wisdom, John P . Charles, Patrick
Hyland, Christian Scholz, Zuntu Xu, Yong Lin, Eli S . Weiss,
Juan L . Chilla, Arnaud Y . Lepert, Coherent, Inc . (United
States)
We report intracavity Raman conversion of a long-wavelength InGaAs-QW
VECSEL to ~1320nm, the longest wavelength ever achieved by a VECSELpumped Raman laser. The set-up consisted of a VECSEL capable of >17W at
1180nm and tunable from 1141-1203nm and 30mm-long KGd(WO4)2 (KGW)
Raman crystal in a coupled-cavity Raman resonator. The Raman cavity was separated from the VECSEL resonator by a tilted dichroic mirror, which steers the Raman beam to an output coupler external to the VECSEL. The spectral emission of the VECSEL, and consequently of the Raman laser, is set by a 4mm-thick quartz birefringent filter in the VECSEL cavity. The KGW
Raman laser is capable of emitting 2.5W at 1315nm, with M^2=2.5 and >4% diode-to-Stokes conversion efficiency. The Raman laser emission is tunable from 1295-1340nm, limited by the free spectral range of the birefringent filter. Spectral broadening of the fundamental emission is observed during
Raman conversion. At the maximum output power the VECSEL, the total linewidth of the output spectrum is ~0.7nm FWHM. As a consequence, the
Raman laser emission is also relatively broad (~0.9nm FWHM). Narrow
(<0.2nm FWHM) emission is obtained by inserting an additional 100?m etalon within the VECSEL cavity. With this configuration the Raman threshold is achieved at lower fundamental intracavity power, suggesting an enhanced effective Raman gain, but the maximum output power of the
Raman laser is 1.8W. Further characterization (power transfers, emission spectra, estimation of the effective Raman gain and thermal lensing power) will be reported.
Optically pumped semiconductor lasers (OPSL) offer the advantage of excellent beam quality, wavelength agility, and high power scaling capability.
In this talk we will present our recent progress of high power 920 nm OPSLs frequency doubled to 460nm for lightshow applications. Fundamental challenges and mitigations are revealed through electrical, optical, thermal, and mechanical modeling. Results also include beam quality enhancement in addressing the competition from diode lasers.
9734-27, Session 7
Michal L . Lukowski, Chris Hessenius, Jason T . Meyer,
Mahmoud Fallahi, College of Optical Sciences, The Univ . of
Arizona (United States)
We report on the development and demonstration of a high power, two color, collinear, blue and green vertical external cavity surface emitting laser
(VECSEL). Two different InGaAs/GaAs VECSEL chips designed to operate
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Conference 9734: Vertical External Cavity Surface
Emitting Lasers (VECSELs) VI around 970 nm and 1070 nm are used to make two separate V-folded laser cavities. Each cavity contains a birefringent filter and a lithium triborate
(LBO) nonlinear crystal oriented such the outputs from two cavities are orthogonal with respect to each other. Two LBO crystals are angle cut to phase match to 970 nm and 1070 nm fundamental wavelengths and provide blue and green outputs via second harmonic generation (SHG), respectively.
These two separate beams are combined in a polarizing beam splitter (PBS) to get a single beam which contains both colors. Thanks to high intracavity circulating power in a VECSEL, over 5 Watts of blue and over 5 Watts of green output power is generated through nonlinear conversion. Overall, a 10 Watt beam made of orthogonally polarized, collinear blue and green wavelengths is presented. This beam can be a great basis for a high power, white laser source, if red output is added in a similar manner.
9734-29, Session 7
Hermann Kahle, Cherry M N . Mateo, Uwe Brauch, Roman
Bek, Univ . Stuttgart (Germany); Thomas Schwarzbäck,
TRUMPF Laser Systems for Semiconductor Manufacturing
GmbH (Germany); Michael Jetter, Thomas Graf, Peter
Michler, Univ . Stuttgart (Germany)
9734-28, Session 7
µ
Peter Holl, Marcel Rattunde, Steffen Adler, Andreas
Bächle, Elke Diwo-Emmer, Rolf Aidam, Wolfgang Bronner,
Joachim Wagner, Fraunhofer-Institut für Angewandte
Festkörperphysik (Germany)
The wide range of applications in biophotonics, television or projectors, spectroscopy and lithography made the vertical external cavity surfaceemitting lasers (VECSELs) an important category of power scalable lasers.
The possibility of bandgap engeneering, inserting frequency selective and converting elements into the open laser cavity and laser emission in the fundamental Gaussian mode leads to ongoing growth of the area of applications for tuneable laser sources. We present an AlGaInP-VECSELsystem with a multi quantum well structure consisting of compressively strained GaInP quantum wells in an Al x Ga 1-x InP separate confinement heterostructure with an emission wavelength around 665 nm. The VECSELchip with its n-? cavity is pumped by a 532 nm Nd:YAG laser under an angle of 50° normal to the surface. In comparison, a gain chip design for high absorption values at pump wavelengths around 640 nm with the use of quantum dot layers as active material is also presented. This leads due to the much better quantum efficiency also to better thermal conditions which again enables power scaling in a defined range. Frequency doubling is now realized with an anti-reflection coated lithium borate crystal, while a birefringent filter, placed inside the laser cavity under Brewster’s angle, is used for frequency tuning.
VECSEL have attracted considerable interest in recent years due to their capability of simultaneously delivering high output powers and a high quality output beam. High-performance VECSELs have been realized at wavelengths ranging from the UV to the near-to-mid IR [1,2].
Using the (AlGaIn)(AsSb) material system, VECSEL covering the 2 – 3 µ m range can be realized. The best laser performance of GaSb-based VECSELs was achieved so far at emission wavelengths around 2.0 µ m with over 30% slope efficiency, a low threshold pump power density of 1.1 kW/cm2 at 20°C heatsink temperature and concomitant a high output power exceeding 7
W in CW operation (depending on the mounting technology) [3]. These parameters were degrading significantly for longer wavelength devices emitting around 2.5 µ m [4] and 2.8 µ m [5]. But for applications like the generation of MWIR light (3-8 µ m) by pumping ZGP-OPOs, high-power
VECSELs around 2.5 µ m are required to suppress absorption losses, while for medical treatment, high-power operation near the water absorption peak at around 2.9 µ m is desirable.
We will present results of our ongoing research strand for further optimization of the semiconductor heterostructure design of longer wavelength GaSb-based VECSELs. By using highly strained QWs with a lattice mismatch of 4.3% we were able to realize a 2.5 µ m emitting VECSEL with very high slope efficiency above 30%, corresponding to an external quantum efficiency exceeding 50%, and a low threshold power density of
0.8 kW/cm2. These values are as good as those for the best performing 2.0
µ m VECSELs. With a front SiC heatspreader and operated in a standard linear cavity, over 7 W of CW output power were achieved for this 2.5 µ m emitting VECSEL structure when operated at 20°C.
We will compare laser structures with different emission wavelengths and discuss the role of the QW strain on laser performance.
References
[1] O. Ochotnikov, Ed., “Semiconductor Disk Laser”, Wiley-VCH, 2010
[2] M. Rahim et al. Appl. Phys. Lett. 95, 241107 (2009)
[3] P. Holl et al, IEEE J Sel Top Quantum Electron. 21 (6), (2015).
[4] Paajaste et al., J Cryst Growth 323, (2011)
[5] Rösener et al., Opt. Lett., 36, (2011)
9734-30, Session 8
(Invited Paper)
Jerome V . Moloney, Isak Kilen, Jörg Hader, College of
Optical Sciences, The Univ . of Arizona (United States);
Stephan W . Koch, Philipps-Univ . Marburg (Germany)
It has been understood for some time that the influence of many-body microscopic carrier-carrier scattering should strongly influence ultrashort optical pulse formation in semiconductor lasers. Our recent simulations show strong departures of electrons and holes from quasi-equilibrium Fermi distributions during short pulse generation in semiconductor disk laser mode-locking. The pulse burns a kinetic hole in the inversion distribution whose depth dictates whether stable single pulses or pulse breakup into multiple pulses will occur. Kinetic hole filling from a nearby unsaturated carrier reservoir can create individual pulses lying outside the net gain window. The filling of this kinetic hole can be qualitatively captured with a dual rate model although the final recovery of the distribution to quasiequilibrium Fermi distributions depends on carrier momentum dependent carrier scattering rates.
In this talk, I will discuss how such nonlinear carrier dynamics affects both gain recovery in the semiconductor disk laser chip and in the saturable absorber mirror (SESAM). We will contrast pulse dynamics in a simple linear cavity and a more commonly utilized V-cavity. Kinetic hole filling when important, feeds carriers into the spectral window supporting the original pulse and leads to an overall amplification of the circulating pulse. Detailed simulations have been carried out varying both saturable and outcoupling losses. Simulation results will be compared with experimental pumpprobe studies of a variety of VECSEL chips and saturable absorber mirror materials. A goal of the study is to see if it is feasible to generate ultrashort, high-energy pulses in a semiconductor disk laser.
122 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9734: Vertical External Cavity Surface
Emitting Lasers (VECSELs) VI
9734-31, Session 8
(Invited Paper)
Michael Jetter, Roman Bek, Hermann Kahle, Quynh Duong-
Ederer, Ana Cutuk, Univ . Stuttgart (Germany); Thomas
Schwarzbäck, Univ . Stuttgart (Germany) and TRUMPF
Lasersystems for Semiconductor Manufacturing GmbH
(Germany); Maria Ana Cataluna, Univ . of Dundee (United
Kingdom); Peter Michler, Univ . Stuttgart (Germany)
Vertical external-cavity surface-emitting lasers (VECSELs) are an important category of power-scalable semiconductor lasers either in continuouswave or pulsed mode. Especially, by introducing a semiconductor saturable absorber mirror (SESAM) into the cavity ultrafast laser sources can be provided. Most research has been done so far in the infrared spectral range from 830 nm to 1.5 µ m, only recently mode-locked VECSEL were realized in the visible and UV spectrum.
We report on our recent advances in passive mode locking of an AlGaInP-
VECSEL emitting at between 650 nm and 665 nm. Both the gain structure and the SESAM are fabricated by metal-organic vapor-phase epitaxy and include a Bragg mirror consisting of 55 ?/4 pairs of Al$_{0.45}$GaAs/
AlAs. The active region and the SESAM contain either GaInP quantum wells or InP quantum dots in an AlGaInP active region in a resonant or anti-resonant design, depending on the divers laser set-ups. We use a v-shaped cavity with a concave output coupler, serving as a folding mirror to tightly focus onto the absorber, with a repetition frequency of ~ 800 MHz.
Depending on the used combinations of gain and SESAM chips, FWHM puls width durations between 250 fs and a few picoseconds were achieved.
Furthermore, we have placed a nonlinear crystal in front of the SESAM to achieve pulsed UV operation around 325 nm with a pulse duration of 1.2 ps.
Next to the laser results, detailed characterization of the used structures will be presented.
9734-32, Session 8
Declan Marah, Univ . College Cork (Ireland); Alexandre
Laurain, College of Optical Sciences, The Univ . of Arizona
(United States); Wolfgang Stolz, Stephan Koch, Antje Ruiz
Perez, Philipps-Univ . Marburg (Germany); John McInerney,
Univ . College Cork (Ireland); Jerome Moloney, College of
Optical Sciences, The Univ . of Arizona (United States)
9734-33, Session 8
(Invited Paper)
Nils Hempler, Walter Lubeigt, Bartlomiej Bialkowski, Craig
J . Hamilton, Gareth T . Maker, Graeme P . A . Malcolm, M
Squared Lasers Ltd . (United Kingdom)
This paper will describe the current state-of-the-art in commercially available, mode-locked Vertical External Cavity Surface Emitting Lasers
(VECSEL). Based on indium gallium arsenide quantum well gain structures, our systems operate with a fixed wavelength in the region between 900 nm – 1060 nm and with Watt-level output powers, low repetition rates of
200 MHz and <500fs durations. Crucially, the paper will discuss power scaling and pulse shortening approaches. In this context, we will discuss aspects of the intracavity heatspreader technology and how this influences the power performance of the systems. Furthermore, we will provide a discussion of how extra-cavity pulse compression techniques can be used to achieve short pulse operation without the need for careful dispersion balance inside the resonator. Full details on the resonator and system design will be given alongside a discussion on how these affect the system’s output characteristics. In addition, the development challenges that have been overcome to bring this promising technology to market will be discussed.
These include: thermal management challenges, electronic control system development and robust mechanical design requirements.
9734-24, Session PTue
Shawn Hackett, Air Force Research Lab . (United States);
Alexander R . Albrecht, Zhou Yang, The Univ . of New
Mexico (United States); Jeffrey G . Cederberg, Sandia
National Labs . (United States); Mansoor Sheik-Bahae, The
Univ . of New Mexico (United States)
An efficient optically pumped vertical external cavity surface emitting laser (VECSEL) operating at 1178nm is demonstrated. The output of this laser is frequency doubled to 589nm with intra-cavity frequency doubling with an LBO crystal for use as a source for sodium guidestar applications.
This represents a novel solution for excitation of the sodium layer of the atmosphere for adaptive optics systems for use with large aperture telescopes. Simulated VECSEL returns from the sodium layer for VECSEL excitation with the Starfire Optical Range’s 3.5m telescope are shown to greatly enhance the utility of current sodium guidestar systems.
Recent development of high power femtosecond pulse modelocked VECSEL with gigahertz pulse repetition rates sparked an increased interest from the scientific community due to the broad field of applications for such sources, such as frequency metrology, high-speed optical communication systems or high-resolution optical sampling. To the best of our knowledge, we report for the first time a colliding pulse modelocked VECSEL, where the
VECSEL gain medium and a semiconductor saturable absorber (SESAM) are placed inside a ring cavity. This cavity geometry provides both a practical and an efficient way to get optimum performance from a modelocked laser system. The two counter propagating pulses in our ring cavity synchronize in the SESAM because the minimum energy is lost when they saturate the absorption together. This stronger saturation of the absorber increases the stability of the modelocking and reduces the overall losses of the laser for a given intra-cavity fluence, leading to a lower modelocking threshold.
This also allows the generation of fundamental modelocking at a relatively low repetition rate (< GHz) with a higher output power compared to conventional VECSEL cavity. We obtained a total output power of 2.2W with an excellent beam quality, a pulse repetition rate of 1GHz and a pulse duration ranging from 1ps to 3ps. The emitted spectrum was centered at 1007nm with a FWHM of 3.1nm, suggesting that shorter pulses can be obtained with adequate dispersion compensation. The laser characteristics and the influence of the relevant parameters on the pulse duration and stability are studied in detail.
9734-34, Session PTue
Theo Chen Sverre, Christopher R . Head, Andy Turnbull,
Edward Shaw, Anne Tropper, Otto Muskens, Univ . of
Southampton (United Kingdom)
It has been occasionally reported that the signal observed in a pump-probe vibrational spectroscopy experiment shows resonant enhancement when successive pump pulses arrive in phase with the vibration mode. The pulse repetition frequency (PRF) of a conventional femtosecond laser is likely,
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Conference 9734: Vertical External Cavity Surface
Emitting Lasers (VECSELs) VI however, to be only 100 MHz, corresponding to a high-order sub-harmonic of the GHz regime resonances exhibited by nanoscale structures. A laser for which the PRF is high enough to excite a mechanical oscillator on every cycle will drive oscillation with amplitude enhanced by at least Q/ π relative to that created by a single pulse. At such a high PRF, it will be necessary to reduce the pulse energy, since heating effects will limit the average power tolerated by the structure under test. The amplitude of vibration induced by the resonant PRF laser will therefore be multiplied by a factor T0*Q/(T π ) relative to that induced by a laser with long interval T between pulses: T0 is the vibration period. For lightly damped resonances with T0 ~ 1 ns and
Q-factor ~ 50 or more, periodic impact excitation starts to be able to access a more highly excited dynamical regime than conventional excitation by isolated pulses. Detection sensitivity is enhanced, and it becomes possible to study nanomechanics in a highly anharmonic regime. Here we report preliminary characterisation of selected nanostructures that promise to be accessible to studies of this kind. The performance of a tunable PRF modelocked VECSEL designed for resonant periodic impact excitation of these structures will be described.
limited output beams and a tuning range of tens of nanometers. Moreover,
VECSELs enable efficient intra-cavity frequency-doubling, reaching the visible and near-ultra- violet range, where there are interesting atomic transitions. Compared to external frequency doubling schemes, an intracavity doubled VECSEL set-up is simpler and can be scaled to higher output powers at the second harmonic.
We report the development of an intra-cavity frequency doubled VECSEL emitting at 570 nm for photo-ionization of Mg atoms. The laser employed a cavity with V- geometry with a gain chip at the end of one cavity arm.
The gain chip had a bottom-emitting design with ten GaInAs quantum wells of 7 nm thickness, which were strain-compensated by GaAsP. Inside the cavity, a critically-phase-matched LBO crystal was used for secondharmonic generation and a birefringent filter and an etalon for wavelength selection. We demonstrated over 2W of single-frequency output power at
570.6 nm. The laser was used to perform Doppler-free modulation transfer spectroscopy of molecular Iodine to generate dispersion shaped error signals suitable for top-of-fringe laser frequency stabilization. Locking to these ~20MHz wide features allows the laser to be stabilized against long term frequency drifts. This work progresses towards externally frequencydoubling the VECSEL’s output to the UV for performing photo-ionization experiments on Mg.
9734-35, Session PTue
Cherry M . N . Mateo, Uwe Brauch, Hermann Kahle, Roman
Bek, Univ . Stuttgart (Germany); Thomas Schwarzbäck,
Univ . Stuttgart (Germany) and TRUMPF Laser Systems for
Semiconductor Manufacturing GmbH (Germany); Michael
Jetter, Marwan Abdou Ahmed, Peter Michler, Thomas Graf,
Univ . Stuttgart (Germany)
9734-37, Session PTue
Shamil Mirkhanov, Adrian H . Quarterman, Conor J . C . P .
Smyth, Samuel Swift, Keith G . Wilcox, Univ . of Dundee
(United Kingdom)
The vertical external cavity surface-emitting laser (VECSEL) offers multi-
Watt continuous wave output powers in fundamental TEM00 mode, diffraction-limited beam quality and wavelength outputs spanning from
UV to mid IR either in the fundamental wavelength or in combination of frequency mixing, making it a versatile type of laser source. While multi-
Watt level output powers in the fundamental wavelength have been demonstrated in the 1 ?m region, above 1 Watt of output powers have been demonstrated in the fundamental wavelength operation of VECSELs in the red spectral range. Such lasers, which are based on the AlGaInP material system, are limited with the pump lasers in the green spectral region and operating temperatures below 0°C. The pumping scheme presented in this contribution demonstrates the enhanced quantum efficiency of an
AlGaInP-based VECSEL, increased operating temperature of up to 50°C and increased output power. The critical role of optimizing the sample design both for the pump and laser wavelengths, pump spot size, and the number of pump light passes are experimentally investigated.
9734-36, Session PTue
Shaun Burd, National Institute of Standards and
Technology (United States) and Univ . of Colorado at
Boulder (United States); Tomi Leinonen, Jussi-Pekka
Penttinen, Optoelectronics Research Ctr . (Finland);
Dietrich Leibfried, Andrew C . Wilson, National Institute of
Standards and Technology (United States); Mircea Guina,
Optoelectronics Research Ctr . (Finland)
GaInAs-based vertical-external-cavity surface-emitting lasers (VECSELs) exhibit advantageous properties for applications in photo-ionization and high precision spectroscopy of several species of atomic ions. Besides offering a broad wavelength coverage between 920 nm and 1.2 µ m, the
VECSEL geometry allows single-frequency emission with close to diffraction
Multiphoton imaging (MPI) of biological samples using VECSELs was first demonstrated in 2011 by R. Aviles-Espinosa et.al [1]. In the initial report of
MPI using a VECSEL, the laser had a peak power of ~350 W, and a pulse duration of 1.5 ps at a repetition rate of ~500 MHz. Much development has been put into reducing the repetition rate of mode-locked VECSELs that leads to lower phototoxicity and better image quality.
However, gigahertz repetition rate VECSELs can now produce few-100-fs pulses at multi-watt power levels and >4 kW peak power. Here we report
MPI using a kilowatt peak power, gigahertz repetition rate femtosecond
VECSEL. The VECSEL we use typically produces 400 fs pulses with an average power of 1.5 W at 1010 nm. It consists of a 10 quantum well gain structure, which is flip-chip bonded onto a thermal diamond and pumped with up to 35 W of 808 nm pump light. The VECSEL was mode-locked using a surface recombination SESAM. The microscope used is a commercially available Nikon TE 2000-U universal microscope with the Radiance 2100
MP as a scanning system. We use Convollaria and C.elegans samples in our experiments since they are relatively stable, and allow repeatable benchmarking of the performance of our VECSEL laser source against commercial laser systems. We also characterize image quality from the
VECSEL MPI systems at 1 GHz and 3 GHz and study how image quality varies with laser parameters such as pulse duration, pulse energy and peak power.
[1] R. Aviles-Espinosa et. al. Biomedical Optics Express, 2, 739-747 (2011).
9734-38, Session PTue
Conor J . C . P . Smyth, Adrian H . Quarterman, Shamil
Mirkhanov, Keith G . Wilcox, Univ . of Dundee (United
Kingdom)
Efficient thermal management is vital for VECSELs as it affects the output power and several aspects of the performance of a device. Presently there exist two distinct methods of effective thermal management which
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both possess their merits and disadvantages. Substrate removal of the
VECSEL gain chip has proved a successful method in devices emitting at a wavelength near 1 µ m. However for other wavelengths the substrate removal technique has proved less effective primarily due to the thermal impedance of the distributed Bragg reflectors. The second method of thermal management involves use of crystalline heat spreaders bonded to the gain chip surface. Although this is an effective thermal management scheme the disadvantages are additional loss and etalon effects that filter the gain spectrum, making modelocking more difficult and normally resulting in multiple peaks in the spectrum. There are disadvantages associated with both methods connected to crystal cost and sample processing. It is for these reasons that the surface liquid cooling thermal management method has been investigated in this project.
Direct liquid cooling involves flowing a temperature controlled liquid over the samples surface. In this project COMSOL was used to model surface liquid cooling of a VECSEL sample in order to investigate and compare its predicted performance with current standard thermal management techniques. Based on modelling, experiments are carried out in order to evaluate the performance of the technique. Conclusions are drawn regarding the future potential of surface liquid cooled VECSEL systems as a low cost alternative to existing techniques.
9734-39, Session PTue
Conference 9734: Vertical External Cavity Surface
Emitting Lasers (VECSELs) VI
Fan Zhang, Mahmoud Gaafar, Christoph Möller, Philipps-
Univ . Marburg (Germany); Wolfgang Stolz, Philipps-Univ .
Marburg (Germany) and NAsP III/V GmbH (Germany);
Martin Koch, Arash Rahimi-Iman, Philipps-Univ . Marburg
(Germany)
9734-40, Session PTue
Alexandre Laurain, Kokou Gbele, College of Optical
Sciences, The Univ . of Arizona (United States); Jorg Hader,
University of Arizona (United States); Wolfgang Stolz,
Philipps-Univ . Marburg (Germany); Stephan Koch, Antje
Ruiz Perez, Philipps-Universität Marburg (Germany);
Jerome Moloney, College of Optical Sciences, The Univ . of
Arizona (United States)
In a typical VECSEL, the relatively low gain requires a highly reflective mirror (>99.8%) attached to the gain medium, and is usually realized with a semiconductor Distributed Bragg Reflector (DBR). However, to reach the reflectivity needed, one has to use lattice matched semiconductor materials with high contrast refractive index, which can be challenging especially with InP based materials. Even with GaAs based material, one has to use
24 pairs of GaAs/AlAs to reach a reflectivity of 99.8%. This relatively thick
DBR stack has a poor thermal conductivity and is a major limitation for high power diamond bonded VECSELs. Here, we demonstrate the realization of a low thermal impedance hybrid metal-semiconductor mirror VECSEL. We used only 14 pairs of AlGaAs/AlAs, transparent at the pump wavelength of 808nm, and we used a patterned mask to deposit pure gold on areas of the chip to be pumped, and Ti/Au on some other area to circumvent the poor adhesion of gold on GaAs. The addition of this metallic mirror requires the DBR region to be finished with an optical phase matching layer.
A higher gain is observed on area metallized with pure gold and an output power of 4W at 1050nm was obtained with an rms fluctuation < 1% over
1 hour of operation. No lasing was obtained on areas metallized with Ti/
Au, showing the effectiveness of the metallic Au mirror and validating the bonding quality. Laser characteristics are studied in details and compared to simulations and chip processing will be discussed.
Vertical-external-cavity surface-emitting lasers (VECSELs) have been proven to be an excellent platform for the realization of high-power multi-mode or single-frequency continuous-wave operation, as well as mode-locked emission. Moreover, because of the emission-wavelength flexibility and the open cavity, this kind of laser is especially attractive to applications requiring intracavity frequency conversion. For instance, in order to develop a powerful continuous-wave terahertz source based on the differencefrequency generation in a VECSEL, several schemes have been realized to produce dual-wavelength emission. However, the separation of the two wavelengths hardly exceeds a few nanometers, being limited by the gain bandwidth of a single VECSEL chip, explaining the approach to go for multichip cavities.
Here, we demonstrate a flexible and compact cavity design, which serially connects two different VECSEL chips in one cavity. Dual-wavelength emission with a wavelength separation of 10 nm and over 600 W intracavity power has been generated. Since the two wavelengths exhibit the same polarization, intracavity type-I second harmonic generation and sumfrequency generation have been performed in a LiNbO3 crystal. This design also shows the potential to offer dual-wavelength emission with other desirable wavelength separations, by employing different chip combinations and filters. Furthermore, we investigate the dependence between the emission wavelengths and intracavity incidence angles on the VECSEL chips, in order to extend the range of accessible wavelengths and thus splittings with this cavity design.
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9735-1, Session 1
Gabor Matthäus, Klaus Bergner, Friedrich-Schiller-Univ .
Jena (Germany); Mawuli Ametowobla, Andreas Letsch,
Robert Bosch GmbH (Germany); Andreas Tünnermann,
Stefan Nolte, Friedrich-Schiller-Univ . Jena (Germany)
Thin-film photovoltaic panels are based on individual solar cells which are monolithically interconnected in series. These interconnections are commonly realized via mechanical micro scribing. In order to reduce the
“dead area” represented by the interconnection zone and hence to increase the net solar output, tightly packed microscopic scribes have to be realized.
For this reason, laser micro-machining gained increasing interest in recent years. However, regarding CIGS thin-film modules, the third structuring stage P3, which is responsible for isolating successive cells, in general suffers from decreased shunt resistance after laser processing.
Here, we demonstrate high-impedance CIGS P3 scribes using ultrashort laser pulses and thermal annealing. During laser processing, we applied various ultra-short pulse laser systems, which delivered different pulse lengths (0.5 - 230 ps) at different wavelengths (388 - 1030 nm) at comparable pulse energies up to several microjoulses. We obtained a wide processing window which allowed a reliable structuring at very high speeds (?10 m/s). Immediately after laser processing, the samples revealed a significant drop in cell performance compared to mechanically processed reference cells, however, after thermal treatment, a permanent performance increase was achieved which outperformed the mechanically structured reference cells. In order to study the underlying annealing effect, we simulated the J-V characteristics using an equivalent circuit model yielding excellent agreement with our experimental results. We show, that the main drawback during ultra-short pulse processing is based on induced defect states at high densities. These defect states can be significantly reduced within minutes by thermal annealing at moderate temperatures.
9735-2, Session 1
Martin Ehrhardt, Pierre Lorenz, Lukas Bayer, Leibniz-
Institut für Oberflächenmodifizierung e .V . (Germany);
Carlos Molpeceres, Univ . Politécnica de Madrid (Spain);
Carlos Antonio Herrera Ramirez, Abengoa Solar Espana
SA (Spain); Klaus-Peter Zimmer, Leibniz-Institut für
Oberflächenmodifizierung e .V . (Germany)
The laser-assisted microstructuring of thin films, especially for electronic applications without damaging the layers or the substrates, is a challenge for laser micromachining techniques. The P3 scribing of copper indium gallium selenide (CIGS) solar cells on different carrier foil was studied using shock-wave-induced film delamination patterning (SWIFD). The delamination process is induced by a shock wave, generated by the laser ablation of the rear side of the carrier foil. The morphology and size of the resultant thin-film structures were studied by scanning electron microscopy (SEM) dependent on the laser parameters. Furthermore, the composition after the laser treatment was analyzed by energy-dispersive
X-ray spectroscopy (EDX). To demonstrate the practical functionality of the SWIFD process the solar cells were electrically characterized after the structuring process. Furthermore, to improve the physical understanding of the process, the delamination process was studied by shadowgraph experiments. The process was simulated using the finite element method, and the simulation results were compared with the experimental ones.
9735-3, Session 1
Andreas Burn, Christian Heger, Berner Fachhochschule
Technik und Informatik (Switzerland); Stephan Bücheler,
Shiro Nishiwaki, EMPA (Switzerland); David Bremaud,
Roger Ziltener, Flisom AG (Switzerland); Lukas Krainer,
Gabriel J . Spuehler, Onefive GmbH (Switzerland); Valerio
Romano, Berner Fachhochschule Technik und Informatik
(Switzerland)
Solar cells based on Cu(In,Ga)Se2 absorbers show the highest efficiencies among all thin-film technologies. Their potential is underlined by efficiency world records of 21.7 percent, demonstrated on cell level (ZSW) and above
16 percent for an entire module (TSCM, Manz). In industrial production of
CIGS solar modules, laser scribing is used for the monolithic interconnection of cells. However, different than in other fields of laser applications, laser scribing never improves solar cell performance but reduces active area, increases series resistance and decreases parallel resistance of the module which all reduce its performance. In the past years we conducted a comprehensive study on laser sources and parameters for selective ablation of photovoltaic thin-films. Various aspects have been analyzed and processes were validated in functional mini-modules. We have demonstrated 16.6 percent efficiency on an all-laser patterned, grid-less
8-cell mini-module. In this module we demonstrated low dead-zone interconnects of <70 µ m width and a high throughput P3 lift-off scribing process, which selectively removes only the front contact of the cell stack. In agreement with results from other groups we reached the highest module performances with a P2 process involving direct ablation of the CIGS layer using picosecond laser pulses. However, necessary high pulse-to-pulse overlap and moderate repetition frequency typically limit the process speed to <200 mm/s which is not compatible with industrial mass production.
In our recent study we optimized P2 scribing processes to overcome this throughput limitation and reach process speeds in excess of 1 m/s. We will present results of our validation experiments using this set of optimized scribing processes.
9735-4, Session 1
Brian J . Simonds, National Institute of Standards and
Technology (United States); Anthony Teal, Tian Zhang, The
Univ . of New South Wales (Australia); Joshua A . Hadler,
National Institute of Standards and Technology (United
States); Zibo Zhou, Sergey Varlamov, Ivan Perez-Wurfl, The
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Conference 9735: Laser Applications in Microelectronic and
Optoelectronic Manufacturing (LAMOM) XXI
Univ . of New South Wales (Australia)
Laser processing for photovoltaics (PV) has traditionally been used for very small dimension features where focused beams are rastered to create lines for edge isolation, scribing, and selective emitter formation and holes for drilling in wrap through style cells. Larger area laser applications are under investigation, for instance in liquid-phase crystallization of thin film Si on glass, however these rely on additional isothermal heat input. We have developed an all-laser processing technique using two industrially-relevant continuous-wave fiber lasers operating at 1070 nm that is capable of both substrate heating with a large defocused beam and material processing with second scanned beam, suitable for a variety of PV processes. We have demonstrated this technique for rapid crystallization of thin film (~10 ?m) silicon on glass, which is a low cost alternative to wafer-based PV. We have also applied this technique to wafer silicon to control dopant diffusion at the surface region where the focused line beam rapidly melts the substrate that then regrows epitaxially. Finite element simulations have been used to model the melt depth. This readily scalable process is carried out in a matter of tens of seconds for an area around 10 cm2 using only about 1 kW of total power. In this talk, we will discuss our results with both c-Si and thin film silicon.
9735-5, Session 2
(Invited
Paper)
Fei He, Shanghai Institute of Optics and Fine Mechanics
(China) and RIKEN Ctr . for Advanced Photonics (Japan);
Junjie Yu, Wei Chu, Zhaohui Wang, Yuanxin Tan, Ya Cheng,
Shanghai Institute of Optics and Fine Mechanics (China);
Koji Sugioka, RIKEN Ctr, for Advanced Photonics (Japan)
Laser writing for selective plating of conductive lines for electronics has several great advantages, compared to conventional printed circuit board technology. Firstly, this method is faster and cheaper for prototyping.
Secondly, material consumption is reduced, because it works selectively.
But the biggest merit of this method is potentiality to produce molded interconnect device, enabling to create electronics in 3D structure, thus saving space, materials and cost of production.
One of the basic techniques of laser writing for selective plating on plastics is Laser Direct Structuring (LDS). In LDS method special fillers are mixed in polymer matrix. These fillers are activated during laser writing process and in the next processing step scanned area can be selectively plated by metals. Thus LDS is a 2-step process. There are some commercial materials available on the market; however, mostly they are based on expensive fillers, usually palladium.
In this work we have investigated new material: polypropylene with carbon based additives. It was tested for LDS approach, using picosecond and nanosecond pulses.
Different laser processing parameters (laser energy, scanning speed, number of scans, pulse durations, wavelength and overlapping of scanned lines) were applied in order to determine the optimal regime of activation. We have measured sheet resistance of selectively plated samples using different laser processing parameters and the same chemical bath conditions. The activation process was also investigated using Raman spectroscopy analysis.
Selectivity tests showed high plating resolution. The narrowest width of plated line was less than 23 ?m. In Raman experiments two spectra of treated and untreated plastic surfaces were compared. Finally, our material was applied for prototype of electronic circuit board on a 2D surface.
9735-7, Session 2
Dirk Mueller, Coherent, Inc . (United States); Andrew Held,
Coherent Inc . (United States); Rainer Pätzel, Coherent
GmbH (Germany); Dave Clark, Coherent, Inc . (Germany);
Joris F . P . van Nunen, Coherent GmbH (Germany)
For higher-density integration and acceleration of operating speed in Si
ICs, 3D integration of wafers and/or dies is essential. Fabrication of current
3D ICs relies on 3D assembly which electrically connects stacked chips to form a single circuit. A key technology for the 3D assembly is TSVs which are vertical electrical connections passing completely through silicon chips to electrically connect vertically assembled Si ICs. Typical TSVs have wide features, with diameters of a range from several microns to 50
?m and depths up to 500 ?m with aspect ratios up to 15 depending on the application and integration scheme. In this work, we present highthroughput, taper-free TSVs fabrication (i.e., 2 ?m-dia. and 5 ?m-dia. vias in
50 ?m-thick and 100 ?m-thick substrates respectively) using femtosecond
Bessel beams operated at different wavelengths from 400 nm to 2.4
?m. In particular, the propagation characteristics of femtosecond laser
Bessel beams during TSVs fabrication are theoretically and experimentally investigated. Furthermore, special phase filters are designed to suppress the damages induced by the side-lobes of Bessel beams for high-quality
TSVs fabrication. Our technique can be potentially used for 3D assembly in manufacture of 3D silicon integrated circuits.
We will provide a detailed look at the most recent technology advancements and emerging laser applications used in the IC packaging industry.
While drilling HDI with CO2 is well established, the mobile device industry’s push for miniaturization is forcing features to be further reduced in size while reducing their manufacturing cost.
To this end carbon-monoxide lasers have recently become commercially available and are operating around 5 µ m wavelength. Their shorter wavelength allows for a smaller focus and hence drilling hole diameters down to 25 µ m whilst keeping the complexity and cost similar to CO2 lasers.
On a separate front, the cost of ownership for Excimer lasers has recently been reduced significantly, which has made this class of lasers attractive for structuring redistribution layers of IC substrates with feature sizes down to
5 µ m. We can now span the gamut from 100 µ m to 5 µ m or µ -via drilling. In addition to demonstrating these new processes, we compare throughput and performance with the more established use of CO2 and ns-UV lasers.
9735-6, Session 2
Karolis Ratautas, Mindaugas Gedvilas, Ina Stankevi?ien?,
Aldona Jagminien?, Eugenijus Norkus, Ctr . for Physical
Sciences and Technology (Lithuania); Nello Li Pira,
Ctr . Ricerche Fiat S .C .p .A . (Italy); Stefano Sinopoli, U .
Emanuele, Bioage Srl (Italy); Gediminas Ra?iukaitis, Ctr . for
Physical Sciences and Technology (Lithuania)
9735-8, Session 2
Seung Hwan Ko, Hyunmin Cho, Dongkwan Kim, Seoul
National Univ . (Korea, Republic of)
Nanowire percolation network has various application as an alternative to
ITO transparent conductor. Laser processing for selecive laser nanowelding was developed for low temperature nanowire annealing process on plastic substrate and used for flexible and stretchable electronics fabrication.
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Conference 9735: Laser Applications in Microelectronic and
Optoelectronic Manufacturing (LAMOM) XXI
9735-9, Session 3
(Invited Paper)
Ajoy K . Kar, Heriot-Watt Univ . (United Kingdom) in microfluidic environments such as 3D electro-orientation of cell motions, dielectrophoretic manipulation of microparticles and electro-rotation in microscale spaces.
Focussed ultrashort laser pulses can modify the local refractive index of certain materials, significant research has been expended into using ultrafast lasers to fabricate integrated optical devices. Integrated optical waveguides – the optical analogue of wires – can be simply fabricated by translating the sample in the path of such short optical pulse trains, which effectively amounts to writing the desired optical circuit in a controlled way in that sample. This direct-write approach offers several key benefits over conventional fabrication techniques. It neither requires use of expensive clean room facilities, nor involves complex film deposition and subsequent etching processes. This technology can also yield 3D structures, unachievable through conventional techniques.
The structural changes induced by the deposited optical energy may manifest themselves in a variety of ways e.g. refractive index and etch-rate changes. Such changes in the properties of the material can in turn be used to create a variety of new and exciting integrated photonic and biophotonic devices. Using the highly localized refractive index modification to directly inscribe optical waveguides in various dielectric materials, we have demonstrated a number of active devices e.g. waveguide amplifiers and mode-locked lasers. Utilizing selective etching we are able to demonstrate cell separator and imaging flow cytometer.
In my talk I will present how the ultrafast laser inscription technology can be used to develop active and passive photonics components. I will also describe how to exploit new materials e.g. laser and highly nonlinear materials, such that several all-optical devices could be monolithically integrated on the same substrate in the form of optical integrated circuits for biophotonic applications.
9735-10, Session 3
Jian Xu, Katsumi Midorikawa, Koji Sugioka, RIKEN (Japan)
9735-11, Session 3
Tetsuya Makimura, Hikari Urai, Univ . of Tsukuba (Japan);
Daisuke Nakamura, Akihiko Takahashi, Kyushu Univ .
(Japan); Hiroyuki Niino, National Institute of Advanced
Industrial Science and Technology (Japan); Tatsuo Okada,
Kyushu Univ . (Japan)
Polydimethylsiloxane (PDMS) is a material used for micro total analysis systems / lab-on-chips due to its flexibility, chemical / thermo-dynamic stability, bio-compatibility and moldability. For further development, it is inevitable to develop a technique to fabricate three dimensional structures in micrometer-scale at high aspect ratio. We have investigated a technique for micromachining of PDMS by means of photo direct machining using laser plasma EUV radiations. The EUV radiations around 10 nm, 13.5 nm, and
11 nm were generated by irradiation of Ta, Sn, and Xe targets, respectively, with Nd:YAG (10 ns) and pulsed TEA CO2 laser (50 ns) light. The generated
EUV radiations were focused on PDMS surfaces at power densities up to 10^8 W/cm2, using an ellipsoidal mirror. Applying the technique, we demonstrated microfabrication of a through hole with a diameter of 1 micrometer in a PDMS sheet. We measured ablation depth using the different EUV sources and found that ablation depth is governed by power density of EUV light on PDMS surfaces.The surfaces are ablated at rates up to 200 nm/shot. From the threshold, the accumulated EUV energy is estimated to be comparable to that to decompose a PDMS surface into small fragments. X-ray photoelectron spectroscopy has revealed that there is no chemical modification induced by the EUV irradiation. All these properties are suitable for micromachining of PDMS elastomers at high aspect ratios.
9735-12, Session 3
Yves Bellouard, Jakub Drs, Ecole Polytechnique Fédérale de Lausanne (Switzerland)
Femtosecond (fs) laser microfabrication allows localized modification in the interior of glass to control physical, chemical and optical properties.
Such modification in three-dimensional (3D) space relies on the intrinsic feature of nonlinear absorption of the fs laser by glass, enabling fabrication of 3D microfluidics and optofluidics for the lab-on-a-chip applications.
Integration of microelectric components into such lab-on-a-chip devices will further enhance functionalities of themselves. Previously we proposed a technique based on hybrid fs laser microfabrication to realize electrofluidics in which microelectric components are integrated into 3D glass microfluidic structures. 3D microchannels with smooth internal walls were first prepared in photosensitive glass by fs laser-assisted chemical wet etching process combined with post-annealing. Then, space-selective metallization of microchannels was achieved by fs-laser direct-write ablation using the same laser followed by electroless metal plating.
In this paper, we demonstrate further progress of this technique in terms of controllability and flexibility in 3D electrode patterning to fabricate highperformance electrofluidic devices. Introduction of water to the ablation site during the laser direct writing realizes debris-free microstructuring of internal walls of glass channels with high controllability and flexibility of laser modification in 3D space. Compared with conventional fabrication methods, electrodes with 3D designable geometries can be facilely prepared at any positions in closed microchannels, which offers the ability of producing 3D controllable electric fields in the channels. Influence of laser processing parameters and electroless plating process on the performance of fabricated devices are discussed. The fabricated electrofluidic devices are applied to demonstrate multifunctional manipulation of biological samples
Morphing refers to the smooth transition from a specific shape into another one, in which the initial and final shapes can be significantly different. A typical illustration is to turn a cube into a sphere by continuous change of shape curvatures.
Here, we demonstrate a process of laser-induced morphing, driven by surface tension and thermally-controlled viscosity. As a proof-of-concept, we turn 3D glass structures fabricated by a femtosecond laser into other shapes by locally heating up the structure with a feedback-controlled CO2 laser.
We further show that this laser morphing process can be accurately modeled and predicted.
9735-13, Session 4
Ioanna Zergioti, National Technical Univ . of Athens
(Greece)
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Conference 9735: Laser Applications in Microelectronic and
Optoelectronic Manufacturing (LAMOM) XXI
During the last decade, laser based techniques have received significant attention as direct, cost-effective and high resolution printing/patterning techniques applied in a variety of applications including sensors, cell printing and microelectronic devices. The versatility that Laser Induced
Forward Transfer (LIFT) offers the capability of its implementation for the fabrication of a variety of sensing devices, i.e. resistive, amperometric, transistor-based optical sensing, and on different substrates. Up to date, the LIFT technique has been applied for the fabrication of several types of biosensors with high spatial resolution in a direct approach. In this work, examples of chemical and biosensors fabricated based on the LIFT technique will be presented. One of the key advantages of LIFT is that can be used as an advanced process for functionalizing the sensors surface, with biomaterials, without the need for intermediate layers, or chemical functionalization techniques, that often require treatment with toxic solvents and hazardous chemicals. The unique characteristic of creating high speed liquid jets, that LIFT technique offers, leads to the physical adsorption of the biomaterials on the sensors’ surfaces.
In addition, following these results, we have introduced Laser Induced
Forward Transfer of liquids method, to characterize the wetting properties of liquid repellent surfaces. With this method, laser pulses are creating liquid jets with very high velocity up to 260 m/s and consequent liquid impact pressures up to 37 MPa. This unique characteristic, along with the capacity to print liquids of various viscosities, makes this technique an ideal candidate to characterize surfaces that withstand high liquid impact pressures without losing their liquid repelling properties, as well as to outline their possible applications.
Wissenschaften München (Germany); Matthias Domke, FH
Vorarlberg (Austria)
Selective and precise structuring of materials with ultrashort laser pulses is based on the electronic absorption of laser energy. Heat generation and diffusion in the electronic system, transfer of energy from the electronic to the lattice system, and the subsequent heat generation and diffusion in the lattice system are the consequence. Finally, at or slightly above the ablation threshold phase transitions and pressure waves are leading to material removal by laser ablation.
Ultrafast time-resolved experiments and numerical simulation are used to generate a deeper understanding of the various kinds of laser ablation, e.g. direct and confined laser ablation for different ultrashort pulse durations.
In this work we present a state of the art overview of the mechanisms of confined laser ablation and the pulse duration dependence of ablation efficiency.
9735-16, Session 5
Corinne Pasquier, Marc L . Sentis, Olivier P . Utéza, Nicolas
Sanner, Lasers, Plasmas et Procédés Photoniques (France) and Aix-Marseille Univ . (France) 9735-14, Session 4
Ming-Tsang Lee, National Chung Hsing Univ . (Taiwan)
In this study, the photo-thermo-fluidic transport phenomena in a novel laser direct synthesis and patterning (LDSP) technology that is applied to rapidly fabricate flexible conductors on a polymer substrate (polyimide film) is investigated. In the manufacturing process, a focused continuous wave green laser beam was directed using a galvanometer system to locally and selectively heat the transparent and particle-free reactive silver ink by the absorption of laser energy from the polyimide substrate. Silver patterns with good electrical conductivity are obtained. The LDSP technology can be operated directly at atmospheric pressure and room temperature. It does not require the use of vacuum chamber, oven and photo-mask, etc.
Therefore, this novel technology offers a new approach to the cost-effective and green fabrication for flexible electronics. The effects of laser power, scanning speed, number of scans and ink concentration on the properties of the resulted silver patterns are investigated both experimentally and theoretically. For the theoretical study, numerical simulations of the transient heat transfer analysis in the microscale heating and chemical reaction spot on the polyimide surface is carried out. Important considerations to the LDSP process on the photo-thermo-fluidic transfer multiphysics are discussed based on the comparison of simulated results and the experimental measurements.
9735-15, Session 5
(Invited Paper)
Heinz P . Huber, Jan Winter, Juergen Sotrop, Regina Moser,
Stephan Rapp, Rudolph Reiel, Hochschule für Angewandte
We present investigations of interaction of a femtosecond laser (down to
15 fs pulse at 800nm) in the single-shot laser regime with the surface of two dielectric materials. We consider fused silica and sapphire, which have different electronic recombination time, when they are exposed to ultrashort pulses.
The first part of our work is to determine the damage threshold (2.0±
0.22 J/cm? for fused silica and for sapphire 2.66±0.24 J/cm?) and the ablation threshold [1] (respectively 2.1±0.17 J/cm? and 2.8±0.23 J/cm?).
Our experimental results confirm that if the pulse duration is short then the two thresholds are close [2]. Secondly, the evolution of the measured transmission, reflexion and inferred absorption signals is studied as a function of fluence. We separate our investigation depending on the incident energy: below ablation threshold, between ablation threshold and the energy below the critical energy in air (for which appear nonlinear propagation effects [3], like Kerr effects or air ionization), and high energy.
The study is completed by a spectral balance in transmission and in reflexion, to identify the absorbed wavelengths and to reveal the spectrum evolution according to the laser incident energy.
A comparative study on the dynamics of energy deposition between a
15-fs pulse and longer pulse durations (30 fs [4] and 450 fs [5]) will be conducted to highlight the advantage of ultra-short pulses, in the context of micromachining applications.
[1] N. Sanner, O. Utéza, B. Bussiere, G. Coustillier, A. Leray, T. Itina, M. Sentis,
Appl. Phys. A 94, (2009) 889–897.
[2] B. Chimier, O. Utéza, N. Sanner, M. Sentis, T. Itina, P. Lassonde, F. Légaré,
J.C. Kieffer, Phys. Rev. B 84 (2011) 094104.
[3] C. Pasquier, P. Blandin, R. Clady, N. Sanner, M. Sentis, O. Utéza , Yu Li,
Shen Yan long, Opt. Commun. 355 (2015) 230–238.
[4] M. Lebugle, N. Sanner, N. Varkentina, M. Sentis, and O. Utéza, J. Appl.
Phys. 116 (2014) 063105.
[5] N. Varkentina, N. Sanner, M. Lebugle, M. Sentis and O. Utéza , J. Appl.
Phys.114 (2013) 173105.
9735-17, Session 5
Olivier P . Utéza, Corinne Pasquier, Raphaël Clady, Nicolas
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Conference 9735: Laser Applications in Microelectronic and
Optoelectronic Manufacturing (LAMOM) XXI
Sanner, Marc L . Sentis, Lasers, Plasmas et Procédés
Photoniques (France)
A critical issue for safe development and operation of emerging laser infrastructures of Petawatt class, combining hundreds of J and sub-15 femtosecond pulses, is the problem of damage of the optical components ensuring the delivery of the ultrahigh intensity beam to the target. The damage evaluation shall be ideally conducted in vacuum to provide the exact conditions of operation for the optical components and materials under test. Indeed, the laser-induced damage threshold (LIDT) is expected to vary depending on the ambiance (air/vacuum) that may affect the energy exchange between the surrounding gas and the material surface.
For instance, considering metals, smaller ablation thresholds have been measured in air compared to vacuum [2]. Nevertheless, performing damage tests in air is of interest for laser manufacturers and optics suppliers, since it enables rapid feedback and comparative assessments for optimization of optical components. However, due to the short duration of the incident pulses and their high sensitivity to nonlinear effects, the preservation of the optical beam properties till the sample located at the focus of a focusing element may be questionable [3].
In this work, we thus address the difficulties implied by the use and manipulation of ultrashort laser pulses in the regime of damage of optical materials. In particular, we determine the exact laser conditions in which the threshold of modification of the material is evaluated. Secondly, to demonstrate the test-bench capabilities, we show the reliable measurement of the laser-induced damage threshold of a material (fused silica) extensively used in photonics.
[1] E. G. Gamaly, N. R. Madsen, M. Duering, A. V. Rode, V. Z. Kolev, and B.
Luther-Davies, Phys. Rev. B 71 (2005) 174405.
[2] C. Pasquier, P. Blandin, R. Clady, N. Sanner, M. Sentis, O. Utéza , Yu Li,
Shen Yan long, Opt. Commun. 355 (2015) 230–238.
9735-18, Session 5
Philipp von Witzendorff, Andrea Bordin, Oliver Suttmann,
Laser Zentrum Hannover e .V . (Germany); Rajesh S .
Patel, James M . Bovatsek, Spectra-Physics® (United
States); Ludger Overmeyer, Laser Zentrum Hannover e .V .
(Germany)
The application of thin borosilicate glass as interposer material requires methods for separation and drilling of this material. Laser processing with short and ultra-short laser pulses have proven to enable high quality cuts by either direct ablation or internal glass modification and cleavage. A recently developed high power UV nanosecond laser source allows for pulse shaping of individual laser pulses. Thus, the pulse duration, pulse bursts and the repetition rate can be set individually at a maximum output power of up to 60 W. This opens a completely new process window which could not be entered with conventional Q-switched pulsed laser sources. In this study, the novel pulsed UV laser system was used to study the laser ablation process on 400 µ m thin borosilicate glass at different pulse durations ranging from
2–10 ns and a pulse burst with two 10 ns laser pulses with a separation of 10 ns. Single line scan experiments were performed to correlate the process parameters and the laser pulse shape with the ablation depth and cutting edge chipping. Increasing the pulse duration within the single pulse experiments from 2 ns to longer pulse durations led to a moderate increase in ablation depth and a significant increase in chipping. The highest material removal was achieved with the 2x10 ns pulse burst. Experimental data also suggest that chipping could be reduced while maintaining a high ablation depth by selecting an adequate pulse overlap. We also demonstrate that real-time combination of different pulse patterns during drilling a thin borosilicate glass produced holes with low overall chipping at a high throughput rate.
9735-19, Session 6
(Invited Paper)
Eeuwe S . Zijlstra, Tobias Zier, Bernd Bauerhenne, Univ .
Kassel (Germany); Sergej Krylow, University of Kassel
(Germany); Martin E . Garcia, Univ . Kassel (Germany)
Intense femtosecond-laser pulses are able to induce ultrafast nonthermal melting of different materials along pathways that are inaccessible under thermodynamic conditions. In order to investigate the nonthermal motion of atoms upon femtosecond laser excitation we performed ab-initio moleculardynamics simulations on laser-excited potential energy surfaces using our code CHIVES (Code for Highly excited Valence Electron Systems).
We found surprising results. Our simulations show that for silicon irradiated below the melting threshold room-temperature phonons become thermally squeezed, and that the presence of squeezed thermal phonons announces complete atomic disordering as a function of fluence, and effect this effect which general and not material specific [1].
Furthermore, by studying irradiated silicon for fluences above the melting threshold, we found that the atoms move successively superdiffusively and fractionally diffusively before becoming diffusive. We found fractional atomic diffusion, not reported so far in materials, during more than 800 fs [2]. In this talk I will show, that combining the effects mentioned above, control of the nonthermal melting process by two pump pulses is possible.
Moreover, simulations of the behavior of thin silicon films upon intense femtosecond laser irradiation show a remarkable effect: nonthermal melting does not start at the surface but in the middle of the film. The various signatures of nonthermal melting and the differences to thermal melting will be discussed.
In order to extend our studies for the study of nucleation phenomena, we developed an analytical interatomic potential for laser-excited silicon, which depends on the electronic temperature. Effects like bond softening in the presence of hot electrons are taken into account. With the help of this potential we were able to perform large-scale simulations and study nucleation dynamics during nonthermal melting.
Finally, it will be shown in this talk that the combination of accurate time-resolved optical measurements with ab-initio calculation of atomic displacements from the knowledge of the reflectivity has clear advantages with respect to time-resolved crystallography and allows a detailed visualization and control of two-dimensional atomic motion in solids [3].
1) E. S. Zijlstra, A. Kalitsov, T. Zier and M. E. Garcia, Squeezed Thermal
Phonons Precurse Nonthermal Melting of Silicon as a Function of Fluence,
Physical Review X 3, 011005 (2013).
2) E. S. Zijlstra, A. Kalitsov, T. Zier and M. E. Garcia, Fractional Diffusion in
Silicon, Advanced Materials 25, 5605-5608 (2013).
3) H. Katsuki, J.C. Delagnes, K. Hosaka, K. Ishioka, H. Chiba, E.S. Zijlstra,
M.E. Garcia, H. Takahashi, K. Watanabe, M. Kitajima, Y. Matsumoto, K.G.
Nakamura and K. Ohmori, All-optical control and visualization of ultrafast two-dimensional atomic motions in a single crystal of bismuth, Nature
Communications 4, 2801 (2013).
9735-20, Session 6
Stephan Rapp, Albert Althammer, Max Bung, Heinz P .
Huber, Hochschule für Angewandte Wissenschaften
München (Germany)
Ultrashort pulsed lasers are gaining increasing significance in industrial
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Conference 9735: Laser Applications in Microelectronic and
Optoelectronic Manufacturing (LAMOM) XXI applications. They offer the advantages of precise and efficient material processing. Thus, intensive research is needed to obtain a fundamental understanding of the physical laser-material interaction. Data showing the ultrafast changes of the optical material properties in response to ultrashort laser pulse processing are still missing. Such data could improve the understanding of ultrafast laser induced phase transitions and their temporal occurrence. Additionally, they could quantify the material absorption change during the pulse impact and possibly explain ablation efficiency changes observed for different pulse lengths. Moreover, these data are important to verify simulated results. In this work, a unique pump-probe ellipsometry microscope is presented to investigate the transient absorption. A laser at a wavelength of 1053 nm and a pulse duration of 650 fs (FWHM) is used as pump source, frequency doubled pulses are used for illumination. The polarization state of the reflected probe-pulse is analysed than to obtain the ellipsometric angles psi and delta and the real and the imaginary part of the complex refractive index. Ellipsometric data acquisition and processing are explained in detail. The setup allows the time-resolved determination of the complex refractive index, describing also the material absorption, with a sub-ps temporal resolution. Measurement series on molybdenum samples are presented. They show the change of the real part (n) as well as the imaginary part (k) of the complex refractive index.
9735-22, Session 7
(Invited Paper)
Nadezhda M . Bulgakova, HiLASE Ctr . (Czech Republic) and
Institute of Thermophysics (Russian Federation); Vladimir
P . Zhukov, Institute of Computational Technologies
(Russian Federation) and Novosibirsk State Technical Univ .
(Russian Federation); Yuri P . Meshcheryakov, Institute of Hydrodynamics (Russian Federation); Tomá? Mocek,
HiLASE Ctr . (Czech Republic)
9735-21, Session 6
Yiming Zhang, Berner Fachhochschule Technik und
Informatik (Switzerland) and Univ . Bern (Switzerland);
Benjamin Lauer, Beat Neuenschwander, Valerio Romano,
Berner Fachhochschule Technik und Informatik
(Switzerland)
Picosecond laser systems have been widely used in industrial microprocessing applications since they are a cost-effective tool to achieve high throughput. To better understand the ablation process , firstly the dependence of the ablation depth and the threshold fluence on the laser spot size were measured utilizing a 10ps pulsed laser system . Further, a
2D axisymmetric model was established to demonstrate the mechanism of the phenomenon. Three sets of the spot radii, namely 15.5?m, 31.5?m and
49.6?m, with equal laser peak fluence ranging from 0.2J/cm2 to 10J/cm2 were applied on copper. It was found that the laser ablation depth in the centre increases with decreasing spot size at identical peak fluence while the ablation threshold is proportional to the spot size. A 2D axisymmetric thermomechanical model was developed to qualitatively illustrate the mechanism of this phenomenon. The equivalent thermal stress, based on von Mises criterion, and the compressive stress were indicated to play a crucial role. Their impact on the ablation depth and threshold fluence is based on the lattice temperature gradient along the surface of the material, leading to spallation and possible mechanical property modifications within the range of lower laser peak fluences. The deviation of the experimental results from the simulation in the case of higher laser peak fluences might derive from the difference between the dynamic process of the experiment and the static approach of the simulation model. This also demonstrates that such a thermomechanical model is better suited for cold ablation with ultrashort pulsed laser because of the lack of the theory describing the stress wave propagation in liquid state.
The interaction of ultrashort laser pulses with transparent optical materials has proven to be a powerful technique of modification of material properties for technological applications based on 3D photonic structures. The physics behind laser-induced modification phenomenon is extremely rich and still far from complete understanding. In this work, the models will be reported which have been developed to describe the processes inside bulk glass induced by ultrashort laser pulses with following material evolution up to microsecond time scale. The most sophisticated model to the date consists of two parts. The first part solves Maxwell’s equations supplemented by the rate and hydrodynamics equations for generated free electrons. The model resolves spatiotemporal dynamics of free-electron population.
Its output in the form of the absorbed energy map serves as the initial condition for thermoelastoplastic model, which yields the final material redistribution. The simulations performed for a wide range of irradiation conditions have allowed to clarify the timescales at which modification occurs after single laser pulses. We demonstrate the ability of the model to quantitatively predict the levels of laser-induced material heating and deformations. The results of simulations of pump-probe experiments have revealed development of defect-mediated screening of laser light. For the linearly polarized laser beam, the effect of light absorption asymmetry is demonstrated. Finally, a new model will be reported for multi-pulse irradiation regimes that takes into account laser beam scanning. Being simplified, this model, however, enables gaining insight into the roles of defects and heat accumulation.
9735-23, Session 7
Mareike Stolze, Thomas Herrmann, Johannes A . L’huillier,
Photonik-Zentrum Kaiserslautern e .V . (Germany)
In recent years, LiNbO3 have been produced considerable interests in a wide field of applications in modern photonics and in surface acoustic wave technologies. Up to date several techniques have been established for the realization of smooth ridge structures in such crystal material, like the processing by ultrashort-pulse laser micromachining. However, not only the fabrication of smooth ridges is interesting even the understanding of the interaction mechanism between ultrashort laser pulse and ferroelectric material is important. The challenge by micromachining LiNbO3 is its outstanding property of pyroelectricity. By inducing a large temperature gradient caused by strong absorption of laser radiation optical damage by cracks could be arise. However, for material removal high excitation intensities in the order of TW/cm? are needed to overcome the bonding force of the solid, which results in a local rise of temperature of several 1000
K within a few microseconds. Thus, thermally driven processes influence significantly the ablation process especially by applying high repetition pulse trains.
We studied the ablation behaviour of congruent, stoichiometric and
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Conference 9735: Laser Applications in Microelectronic and
Optoelectronic Manufacturing (LAMOM) XXI chemically reduced LiNbO3 by using ultrashort laser pulses. The influence of crystal orientation as well as of wavelength and pulse duration on the laser induced damages will be presented. Based on the experimental results we propose a first model that addresses the charge transport by high intensity excitation with ultra-short laser pulses. Further, we are taking the advantage of processing smooth ridges with high-repetition UV picosecond laser-pulses and a low-loss ridge waveguide in congruent LiNbO3 will be demonstrated.
9735-24, Session 8
Malte Kumkar, Myriam Kaiser, Jonas Kleiner, TRUMPF
Laser- und Systemtechnik GmbH (Germany); Daniel
Grossmann, TRUMPF Laser- und Systemtechnik GmbH
(Germany) and RWTH Aachen Univ . (Germany); Daniel
Flamm, TRUMPF Laser- und Systemtechnik GmbH
(Germany); Klaus Bergner, Stefan Nolte, Friedrich-Schiller-
Univ . Jena (Germany) femtosecond lasers, laser filamentation opens the door to an even wider application area. To achieve a basically zero-gap cutting or perforation line, those laser-generated filaments are placed close to each other by a relative movement of the work piece and/or the processing head at typical speeds of 100–1000mm/s, depending on the material thickness and the desired cut geometry.
Suitable ultrafast lasers for the filamentation process have been developed, built up as a MOPA chain to allow for very high repetition rates and the burst mode option, which provides pulse packages with nanosecond separation and programmable power slopes.
The presentation will give an overview on the fundamentals of laser filamentation by comparing numerical simulation data with experimental results and will describe the influence of the most important parameters of ultra short pulsed lasers on the formation of filaments. Examples for successful industrial applications will be presented to demonstrate the huge potential of that technology.
9735-43, Session PTue
Wisnu Setyo Pambudi, Masayuki Okoshi, National Defense
Academy (Japan); Tsugito Yamashita, Kanto Gakuin Univ .
(Japan)
We report on developing industrial NIR ultrafast laser processing of transparent materials based on nonlinear absorption. The targeted applications are industrial front and rear side ablation, drilling and inscription of modification for cleaving and selective laser etching of glass and sapphire in sheet geometry.
We applied pump probe technology and in situ stress birefringence imaging for fundamental studies on the influence of energy and duration (100 fs – 20 ps), temporal and spatial spacing, focusing and beam shaping of the laser pulses.
By pump probe technique we are able to visualize differences of spatiotemporal build up of absorption, self focusing, shock wave generation for standard single spot, multi spot and beam shaped focusing. Incubation effects and disturbance of beam propagation due to modifications or ablation can be observed.
In-situ imaging of stress birefringence gained insight in transient build up of stress with and without translation. The results achieved so far demonstrate that transient stress has to be taken into account in scaling the laser machining throughput of brittle materials. Furthermore it points out that transient stress birefringence is a good indicator for accumulation effects, supporting tailored processing strategies.
We correlate the findings from in-situ diagnostics with ex-situ analysis.
Some application results will be shown for display cutting, for drilling by selective etching of laser induced modifications or ablation.
Periodic micro/nanostructuring of silicone rubber surface was induced by the irradiation of 193 nm ArF excimer laser. The ArF laser was focused on the surface of silicone rubber by each microsphere made of silica glass of 2.5 micron diameter, which covered the entire surface of the silicone. The singlepulse fluence and irradiation time of the ArF laser were approximately 10 mJ/cm2 and 1 min, respectively. The pulse repetition rate was 1 Hz. The silicone rubber surface underneath each microsphere selectively swelled due to the photodissociation of Si-O bonds of silicone into the lower molecules during the ArF laser irradiation. From the observations by an optical microscope and atomic force microscope, the formed micro/nanostructures were also found to be periodical: they were formed at regular intervals of approximately 2.5 micron. Contact angle of water was measured to see hydrophobicity of the samples; it showed approximately 150 degrees on the micro/nanostructured silicone, indicating a clear super-hydrophobic property.
9735-25, Session 8
Roland M . Mayerhofer, Rofin-Baasel Lasertechnik GmbH
& Co . KG (Germany); Abbas S . Hosseini, ROFIN-Sinar, Inc .
(United States)
Glass and other brittle, transparent materials offer unique properties, that will fuel a continuously growing use in consumer electronics, medical devices, integrated circuits, architectural, automotive, aerospace and a variety of other interesting market segments. Due to low absorption in the visible and infrared spectrum and a typically low thermal-shock resistance, laser processes on glass have always been challenging.
Beside the successfully established fusion cutting technology using pulsed fiber lasers especially for sapphire and ceramics, as well as the option to perform an ablation cut through thin brittle materials by pico- or
9735-44, Session PTue
Kazuyuki Uno, Takuya Yamamoto, Miyu Watanabe, Tetsuya
Akitsu, Univ . of Yamanashi (Japan); Takahisa Jitsuno,
Osaka Univ . (Japan)
Transparent dielectric materials including SiO2 glass absorb infrared light efficiently. We developed a short-pulse CO2 laser (9.2 – 11.4 ?m) pumped by a longitudinally excitation scheme. The laser pulse waveform of our CO2 laser has a spike pulse with a pulse width of about 100 ns and an energy of several mJ, and a pulse tail with a controllable energy (about 0 – 50 mJ).
The spike pulse gives ablation process and the pulse tail gives heat process.
Therefore, in this work, we investigated SiO2-glass drilling characteristics depended on the pulse-tail energy, the fluence, and the number of shots.
In the longitudinally excited CO2 laser, the laser tube consisted of a 45-cmlong alumina ceramic pipe with an inner diameter of 9 mm, a ZnSe output coupler (R85%), and a high-reflection mirror with (r20 m). The laser pulse waveform was controlled by an excitation circuit, an input energy and medium gas. Several types of laser pulse waveforms (for example, the same spike-pulse energy of 1 mJ and the different pulse-tail energy of 7 mJ, 12 mJ
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Conference 9735: Laser Applications in Microelectronic and
Optoelectronic Manufacturing (LAMOM) XXI or 21 mJ) were focused with a ZnSe lens with a focal length of 5 cm.
Higher pulse-tail energy produced the deeper ablation depth at the same spike-pulse energy or the same fluence. Moreover, in a SiO2 glass with a thickness of 300 ?m, drilling a through hole with the diameter of 88
?m (back side 56 ?m) was demonstrated. We try efficiently drilling small through holes by our short-pulse CO2 laser with controllable pulse-tail energy.
CO2 laser fusion splicer can produce results within the breaking strength range of pristine (un-stripped, un-spliced) fiber. Improvements in fiber preparation methods (especially fiber stripping and cleaning) can enable better exploitation of the high strength splicing benefits of laser fusion splicing.
9735-45, Session PTue
Eric T . Basso, Yasuyuki Ninomiya, AFL (United States)
Modern demand for miniaturization has driven the development of increasingly compact, reliable, and low-cost fiber-based components for use in a variety of applications in the medical, sensing, and telecom fields.
The availability of these increasingly complex components is credited to glass processing technology that enables engineers to develop repeatable fabrication processes for glass processing machines.
These machines offer great flexibility, capable of controlling the position, motion, imaging, and heating of optical fibers, but their complexity often makes development lengthy and difficult. This is especially true of more advanced components, such as lensed fibers, tapered ball lenses and multi-tapered fibers, requiring long hours of development for engineers and specially trained operators for fabrication that often needs multiple passes and operator assistance.
In this paper, we detail an improved graphical user interface for defining single-pass novel shaping techniques. It is a C# program capable of creating shaping sequences through a mixer-like interface, directly manipulating execution timelines, motor properties and logic blocks in one easy to read window. This allows users who can “talk through” a process to easily translate concept to instructions. This window works in tandem with a customizable data collection module and video feed, allowing users to collect relevant data and fine-tune processes with one program. This approach seeks to offer unique modularity and debugging capability to researchers and operators during the process development and production phases, as well as easy translation of any conceivable machine instructions to a controllable, repeatable command stack.
9735-47, Session PTue
Lei Yuan, Clemson Univ . (United States); Jie Huang,
Missouri Univ . of Science and Technology (United States);
Jie Liu, Yang Song, Qi Zhang, Jincheng Lei, Hai Xiao,
Clemson Univ . (United States)
Research and development in photonic micro/nano devices and structures have experienced a significant growth in recent years, fueled by their broad applications as sensors for in situ measurement of a wide variety of physical, chemical and biological quantities. Recent advancement in ultrafast and ultraintense pulsed laser technology has opened a new window of opportunity for one-step fabrication of micro- and even nano-scale 3D structures in various solid materials. When used for fabrication, fs lasers have many unique advantages such as negligible cracks, minimal heataffected-zone, low recast, and high precision. These advantages enable the unique opportunity to fabricate integrated sensors with unprecedented performance, enhanced functionalities and improved robustness.
In this paper, we summarize our recent research progresses on the understanding, design, fabrication, characterization of various photonic sensors for energy, defense, environmental, biomedical and industry applications. Femtosecond laser processing/ablation of various glass materials (fused silica, doped silica, sapphire, etc.) will be discussed towards the goal of one-step fabrication of novel photonic sensors and new enabling photonic devices. A number of new photonic devices and sensors will be presented.
9735-46, Session PTue
Usman B . Nasir, Douglas M . Duke, AFL (United States); Elli
Saravanos, Corning Cable Systems LLC (United States)
The use of a CO2 laser as a heat source became commercially available for optical fiber splicing and component fabrication only in recent years.
In addition to long-term trouble-free and low-maintenance heat source operation, laser fusion splicing offers unique benefits for fabrication of highpower optical components, as well as for splice strength.
CO2 laser heating is different from other heating methods in that the power from the CO2 laser beam is efficiently absorbed by the outer layer of the glass, which in turn conducts the energy inwards. In this case, there is no consumable heating element such as electrodes or resistive filaments that may leave contaminants or deposits on the glass surface.
The CO2 absorptive heating can also be very well controlled, with minimal vaporization and re-deposition of the glass itself. The CO2 laser beam can be guided and shaped for processing certain fiber types and combinations that do not process well by other methods. CO2 laser enables radiative heating in addition of absorption, permitting glass processing techniques that are not supported by alternative heating methods.
Heating by a CO2 laser results in a contamination-free glass surface, with little surface damage or irregularity, hence contributing to remarkable physical (splice) strength. Splice strength data in Figure-1 shows that the
9735-48, Session PTue
Jörn Bonse, Robert Koter, Manfred Hartelt, Dirk Spaltmann,
Simone Pentzien, Bundesanstalt für Materialforschung und -prüfung (Germany); Sandra Höhm, Arkadi
Rosenfeld, Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie (Germany); Jörg Krüger,
Bundesanstalt für Materialforschung und -prüfung
(Germany)
Laser-induced periodic surface structures (LIPSS, ripples) were generated on steel and titanium surfaces upon irradiation with multiple linear polarized femtosecond laser pulses (pulse duration 30 fs, central wavelength 790 nm). The experimental conditions (laser fluence, spatial spot overlap) were optimized in a sample-scanning geometry for the processing of large surface areas covered homogeneously by the nanostructures. The irradiated surface regions were subjected to optical microscopy (OM), white light interference microscopy (WLIM) and scanning electron microscopy (SEM) revealing sub-wavelength spatial periods. The nanostructured surfaces were tribologically tested under reciprocal sliding conditions against a sphere of hardened 100Cr6 steel at 1 Hz using paraffin oil and engine oil as lubricants. After 1000 sliding cycles at a load of 1.0 N, the corresponding wear tracks were characterized by OM and SEM. For specific conditions the laser-generated nanostructures endured the tribological treatment.
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Conference 9735: Laser Applications in Microelectronic and
Optoelectronic Manufacturing (LAMOM) XXI
Simultaneously, a significant reduction of the friction coefficient was observed in the laser-irradiated (LIPSS-covered) areas when compared to the non-irradiated surface, indicating the potential benefit of laser surface structuring for tribological applications.
9735-49, Session PTue
Moritz Grehn, Technische Univ . Berlin (Germany); Thomas
Seuthe, Fraunhofer-IKTS CMD (Germany); Michael Höfner,
Nils Griga, Technische Univ . Berlin (Germany); Alexandre
Mermillod-Blondin, Max-Born-Institut für Nichtlineare
Optik und Kurzzeitspektroskopie (Germany); Markus
Eberstein, Fraunhofer-IKTS CMD (Germany); Jörn Bonse,
Bundesanstalt für Materialforschung und -prüfung
(Germany)
The role of glass composition on its fs-laser ablation threshold fluence is of ongoing discussion. In this study, silica based binary and ternary glasses are investigated with respect to their ablation fluence threshold upon the irradiation of 120 fs, 800 nm laser pulses. With the alteration of the stoichiometry of the glasses, the influence of the composition to their fs- laser ablation threshold is investigated. The absorbed energy density at the ablation threshold is estimated by a multiphoton absorption model.
This energy density is compared to a calculated energy density which is needed to decompose the glass into its atomic constituents. Within the experimental accuracy, both quantities are in good agreement. Hence, it is concluded that the laser ablation fluence threshold is driven by two antagonistic parameters: the binding energies of the molecule orbitals in the glass compound which opposes the excitation energy provided by the absorbed fraction of the laser pulse. If the excitation of the material overcomes the binding forces the material decomposes and ablation becomes manifest. The model used for the quantity of absorbed energy density allows also for an assessment of the surface topography. Therefore, crater topographies are compared to the model and are found to be in good agreement with the crater profiles obtained by atomic force microscopic measurements.
9735-50, Session PTue
Aleksandr P . Zhevlakov, ITMO Univ . (Russian Federation);
Ruben P . Seisyan, Ioffe Physical-Technical Institute
(Russian Federation); Viktor Bespalov, Valentin Elizarov,
National Research Univ ITMO (Russian Federation);
Alexsandr S . Grishkanich, Sergey V . Kascheev, ITMO Univ .
(Russian Federation)
The power consumption in the two-pulse bispectral primary source could be substantially decreased by replacing the SRS converters from 1.06 µ m into
10.6 µ m wavelength as the preamplifier cascades in ??2 laser channel at the same efficiency radiation of EUV source.
The creation of high volume manufacturing lithography facilities with the technological standard of 10-20 nm is related to the implementation of resist exposure modes with pulse repetition rate of 100 kHz.
One of the promising schemes supporting such mode is based on the extreme ultraviolet (EUV) radiation emitted from plasma formed by illumination of target with a focused laser beam. The main power pulse comes from the ??2 laser with a certain time delay, thereby increasing the conversion efficiency.
The effect of a gigantic image contrast transfer in the nonlinear inorganic resist observed under illumination by the high-intensity radiation provides a high resolution of the integrated circuit (IC) topology elements. It contains the master oscillator SSL, stimulated Raman scattering (SRS) conversion cascades and the ??2 amplifier.
In this scheme SSL serves for preliminary target heating and plasma initiation and as a pump source for the series of SRS converters. Radiation of the second Stokes component with the wavelength of 10.6 µ m from the final
SRS converter is injected into the ??2 amplifier as an input. Note that in this case the SRS converters do not require a power supply. They are pumped solely by the low power SSL radiation with wavelength of 1.06 µ m and the first Stokes component obtained from the conversion of this radiation.
Several rotated mirrors are set for adjustment of the time delay between the preliminary and main pulses in the final SRS cell containing hydrogen by pressure of 60 bar. Low power consumption of the proposed scheme makes it promising for the creation of LPP EUV sources.
9735-26, Session 9
Rudolf Reiel, Christoph Aichele, Stephan Rapp, Jürgen
Sotrop, Heinz P . Huber, Hochschule für Angewandte
Wissenschaften München (Germany)
Selective laser structuring of thin molybdenum layers from the glass substrate side using ultra-short pulses can exhibit up to a factor of 10 higher ablation efficiencies compared to direct ablation. Observations suggest that ultrafast heating followed by thermal expansion in the metal generates an propagating pressure wave leading to bulging of the metal. In this study time resolved measurements of the transmittance and reflectivity by a transmission enhanced pump-probe microscopy setup was used to monitor the ablation process of a 10 nm to 50 nm thick Mo layers on a glass substrate. The generated transient signal is superimposed by oscillating features, which can be discriminated to interference caused by moving interfaces with different refractive indexes. The sources have been identified as a sound wave in glass (5880 m/s), a shock wave in air (1000-3000 m/s) and the motion of the metal layer (60-200 m/s). Taking energy conservation into account the lack of light caused by scattering and absorption can be calculated with the obtained transmission and reflection data. It is shown that this light extinction is rising with growing fluences above the ablation threshold. Additionally, it has been noticed that under the precondition of reaching the vaporization threshold in the center of the laser pulse, the size of the removed metal layer equals the area where the melting threshold is reached.
9735-27, Session 9
Regina Moser, Jürgen Sotrop, Heinz P . Huber, Hochschule für Angewandte Wissenschaften München (Germany);
Gerd Marowsky, Laser-Lab . Göttingen e .V . (Germany)
Confined laser ablation by ultra-short laser pulses is an innovative technique for precise micromachining. It has recently been shown that the energy of the laser pulse is confined between an absorbing and transparent layer, which enables high precision and energy efficient processes. This study compares experimental data of confined laser ablation with numerical simulation. The laser pulse is transmitted through a transparent silicon
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Conference 9735: Laser Applications in Microelectronic and
Optoelectronic Manufacturing (LAMOM) XXI dioxide (SiO2) layer and absorbed by silicon (Si) substrate. In this confined two layer system, ablation of the SiO2 occurs. The energy is partially absorbed and reflected by the electronic-system, which is simulated with the Drude-model for semiconductors. The electron-photon coupling interaction and subsequent heat transfer by the lattice-system initiated by the ultra-short laser pulse is simulated with a two-temperature model.
The simulation results agree with previous pump-probe measurements that reflection is time-dependent. The results also show a gas-liquid mixture at the SiO2/Si interface, with a different reflection index. The volume of the gas-liquid mixture and the thermo-mechanical bulging have good agreements with the SiO2 bulging well known from accepted pump-probe measurements. These important observations suggest that this novel numerical simulation can be utilized to predict and analyze the ablation behavior of similar two layer systems.
technology represents the method of choice for the deposition of highly uniform functional thin-films from solution onto arbitrary substrate materials on large areas. Direct writing by means of selective patterning with ultrashort pulse laser ablation will be utilized to generate the desired patterns on previously deposited thin-films. Special techniques of direct and confined laser ablation will be applied to achieve selective structuring of the films, without damaging adjacent layers, with a lateral resolution in the ?m-region. Either selective contact opening (for conductive interconnections) or isolating lines can be realized. Both functions are important for the different device architectures. Ultrafast pump-probe microscopy with a temporal resolution of about 1 ps is used to show fundamental aspects of the laser ablation process.
9735-28, Session 9
Stephen Ho, Prasoon Jha, Peter R . Herman, Univ . of
Toronto (Canada)
Femtosecond laser interactions inside thin transparent dielectric films of refractive index, nfilm, with tight focusing presents strong nonlinear interactions that can be confined at the Fabry-Perot fringe maxima to generate thin nanoscale plasma disks of 20 to 45 nm thickness separated on half-wavelength, ?/2nfilm. This thin-film interference drives nano-disk explosions which in turn enable nano-cleaving of subwavelength internal cavities at single or multiple periodic depths at low laser exposure. Higher laser exposure will otherwise lead to a controlled digital ejection at fractional film depths with quantized-depth thickness defined by the laser wavelength.
In our previous work, we have already developed and demonstrated quantized ejection and formation of nanocavities in SiNx film with laser wavelengths of 522 nm 800 nm and 1044 nm. The present paper extends this high-resolution nano-cleaving to inside thin films for SiOx to create nanoblisters of various sizes that open sub-wavelength nanocavities with thin membranes at single or multiple periodic depths. This opens a new lab-in-film direction to form nano-fluidic channels for submicron particle detection and sensing in a SiOx thin film that has the advantageous properties of chemical inertness, optically transparent, high wettability, and low autofluorescence. Further, this thin film nanostructuring opens the opportunity of integrating numerous functionalities onto devices which already employed thin films, including CMOS microelectronics and photonics, photovoltaics, LED, lab-on-chips, and MEMS. The process window is extended to short laser wavelength of 343 nm, and further examined over the limits of laser pulse duration and coherence for producing fractional film ejections, and open and closed nanoblisters.
9735-30, Session 10
(Invited Paper)
Jörn Bonse, Bundesanstalt für Materialforschung und -prüfung (Germany); Sandra Höhm, Arkadi
Rosenfeld, Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie (Germany); Jörg Krüger,
Bundesanstalt für Materialforschung und -prüfung
(Germany)
During the past few years significantly increasing research activities in the field of laser-induced periodic surface structures (LIPSS, ripples) have been reported since the generation of LIPSS in a single-step process provides a simple way of surface nanostructuring towards a control of optical, mechanical or chemical surface properties.
In this contribution the current research state in this field is reviewed.
The formation of LIPSS upon irradiation of metals, semiconductors and dielectrics by multiple linearly polarized Ti:sapphire fs-laser pulses (duration:
30-150 fs) is studied experimentally and theoretically. Different types of
LIPSS with periods even below 100 nm can be generated. Their dynamics and formation mechanisms are analyzed and identified in ultrafast optical experiments (time-resolved diffraction & polarization controlled doublepulse experiments at different wavelengths). Complementing theoretical calculations of the laser-induced carrier dynamics address transient changes of the optical properties of the irradiated materials and reveal the importance of surface plasmon polaritons in the early stage of LIPSS formation. Various applications of these nanostructures are outlined. Their beneficial effect on the tribological performance is demonstrated for metals.
9735-29, Session 9
Juergen Sotrop, Heinz P . Huber, Hochschule für
Angewandte Wissenschaften München (Germany)
9735-31, Session 10
Xiaolong He, Purdue Univ . (United States) and Harbin
Institute of Technology (China); Woongsik Nam, Xianfan
Xu, Purdue Univ . (United States)
Random carbon nanotube (CNT) networks have raised a continuously increasing interest among a broad and multidisciplinary community of researchers throughout the last decade. The remarkable and concurrently diverse properties of such networks have rendered them suitable for a wide range of applications in science and engineering. Among the most promising applications are transparent conductive electrodes, thin-film transistors and circuits, mechanical and chemical sensors. To produce such novel devices, two key technologies are combined: Scalable spray
For the past decades, advances in optical techniques and processing have achieved a rapid reduction in the feature size of nanostructures. In particular, optical lithography has been the primary tool to create fine-scale patterns required for nano-fabrication. However, the diffraction nature of light is a barrier for achieving nanometre feature and resolution in conventional optical lithography, and various ways have been attempted to achieve subdiffraction limited patters e.g. [1]. Direct writing of laser-induced periodic surface structures (LIPSS) has been an area of ongoing examination for over a decade as a flexible and low-cost method to create nanostructures with periods significantly smaller than the laser wavelength. LIPSS can be easily formed on nearby all kinds of materials, including metals, semiconductors,
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Conference 9735: Laser Applications in Microelectronic and
Optoelectronic Manufacturing (LAMOM) XXI and insulators[2-4], but the quality and the random nature of LIPSS are still the remained obstacle for some applications.
In this work, we demonstrate a laser-direct-writing technique to exploit
LIPSS far below the diffraction limit. The technique has the capability to create a single line which is unlike other LIPSS techniques where only multiple, periodic line structures can be formed. In addition, the approach is low-cost, maskless, and highly flexible. The formation of LIPSS is carefully controlled on SU-8 photoresist. Effects of exposure power, polarization direction and scan speed are observed respectively. Nanostructure less than
50 nm feature size is obtained and characterized using scanning electron microscopy and atomic force microscopy, as shown in Fig. 1. We expect that our approach could be a promising alternative for high-resolution lithography with its simplicity and flexibility.
of graphene from step and terrace regions using 4 ° off-cut 4H-SiC(0001) substrates.
The KrF excimer laser with a wavelength of 248 nm was used as a local heating source on the SiC surfaces. Pulse duration of the laser was 55 ns, and repetition rate was 1000 Hz. Si atoms are preferentially sublimated from the SiC surface by the laser irradiation, and graphene growth is induced by the rearrangement of surplus carbon on the SiC surface. The graphene growth was performed in ambient Ar of 500 Pa.
C-AFM images obtained by simultaneous measurements of the surface morphology and local current revealed that graphene formation starts from step region on the SiC(0001) surface at the irradiation number of
3,000 shots, and the graphene formation regions expand to terrace region at 5,000 shots. From results of HR-TEM measurements, the number of graphene layers increases with increasing the laser irradiation number, and
5-7 layers graphene is formed at 20,000 shots.
9735-32, Session 10
Lara Bauer, TRUMPF Laser GmbH (Germany) and Univ .
Stuttgart (Germany); Simone Russ, TRUMPF Laser GmbH
(Germany); Myriam Kaiser, Malte Kumkar, Birgit Faisst,
TRUMPF Laser- und Systemtechnik GmbH (Germany);
Rudolf Weber, Thomas Graf, Univ . Stuttgart (Germany)
9735-34, Session 11
Tao Zhang, Seungkuk Kuk, Stony Brook Univ . (United
States); Eunpa Kim, Costas P . Grigoropoulos, Univ . of
California, Berkeley (United States); David J . Hwang, Stony
Brook Univ . (United States)
Glass has recently found increasing importance in industrial markets, especially in the rapidly growing sector of display or cover glass applications for consumer electronics. However, cutting of brittle materials is a demanding process since high quality standards are required. Cutting with ultrafast lasers has great potential for processing brittle materials efficiently without time consuming post-processing operations. However, the interaction of ultra-short laser pulses with transparent materials is not yet understood well enough to determine how to simultaneously increase the edge quality, the efficiency of the process and the productivity.
The present work investigates the influence of the pulse duration and the temporal spacing between pulses on the ablation of aluminosilicate glass by comparing the results obtained with laser pulses with durations of 400 fs,
900 fs and 6 ps. For 1 and 0.4 ps the ablation threshold fluences are lower than for 6 ps. For 0.4 ps pulses we found an increased ablation threshold fluence compared to the ablation threshold fluence of 1 ps pulses. We found that surface modifications occur already at fluences below the single pulse ablation threshold and that laser-induced periodic surface structures
(LIPSS) emerge as a result of those surface modifications. Scanning electron micrographs of LIPSS generated with 0.4 ps laser exhibit a more periodic and less coarse structure as compared to structures generated with 6 ps.
Furthermore we will report on the influence of temporal spacing of the pulses on occurrence of LIPSS and the impact on the quality of the cutting edge.
Lasers have proven to be unique tools for a highly selective processing of nanomaterials system on the basis of the enhanced laser field, maintaining other sensitive portion in the system untouched. However, in many practical applications, a wide interspacing distribution among nanomaterials and nonlinear laser absorption properties of the nanomaterials in the highly excited nanomaterials states, frequently lead to rather adverse effects in terms of controlled nanomaterials processing. In this study, we will take a few laser nanomaterials processing examples mainly based on the nanowires system including the sprayed metallic nanowires for transparent electrode applications and selective semiconductor nanowires growth from the metallic nanocatalysts, and discuss on the role of the enhanced laser field via the combined theoretical and experimental investigations. Specific aims of properly utilizing the enhanced laser fields are to achieve improved electrical conductance for practical transparent electrode applications, and to facilitate directed growth of semiconductor nanowires at designated sample locations, respectively.
9735-35, Session 11
Keegan J . Schrider, Ben R . Torralva, Steven M . Yalisove,
Univ . of Michigan (United States)
9735-33, Session 11
Masakazu Hattori, Hiroshi Ikenoue, Daisuke Nakamura,
Tatsuo Okada, Kyushu Univ . (Japan)
We have proposed a novel direct growth method of graphene on SiC
(0001) surfaces by KrF excimer laser irradiation and we observed growth processes of the graphene by conductive-AFM (C-AFM) measurements.
In our previous reports, we conclude that double layers graphene can be formed by laser irradiation of 1.2 J/cm2 and 5000 shots, and grain size of the graphene is about several tens nm. In the C-AFM images, the formation region of graphene can be observed as current spots because graphene has low conductively. In this report, we investigate local growth processes
Nano crystalline metals possess extraordinary mechanical properties including increased wear resistance and strength, but they are often unstable and exhibit grain coarsening at relatively low temperatures so their desirable properties quickly degrade. It has been shown that electrodeposited nanocrystalline Ni-W alloys are stabilized by the weak segregation of W to Ni grain boundaries [1]. This talk will describe our work to create similar, stable nanocrystalline alloys by mixing metals via ultrafast laser irradiation. We will present Transmission Electron Microscopy demonstrating the intermixing of sputtered multilayer films of Ni and W, and showing the microstructure of the resulting Ni-W alloy. If time permits we will address how the weight percent of Ni and W, the thickness of Ni and W layers, and laser fluence effect the microstructure.
[1] Detor, AJ. and Schuh, CA., “Tailoring and patterning the grain size of nanocrystalline alloys.” Acta Mater. 55, 371–379 (2007).
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Conference 9735: Laser Applications in Microelectronic and
Optoelectronic Manufacturing (LAMOM) XXI
9735-36, Session 11
Daisuke Nakamura, Tetsuya Shimogaki, Toshinobu Tanaka,
Fumiaki Nagasaki, Yuki Fujiwara, Mitsuhiro Higashihata,
Tatsuo Okada, Kyushu Univ . (Japan)
To guarantee the required excellent accuracy even at high scanning speeds a new interferometry based encoder technology was used, that provides a high quality signal for closed-loop control of the galvo scanner position.
Low inertia encoder design enables a very dynamic scanner system which can be driven to very high line speeds by a specially adapted control solution. We will present results with marking speeds up to 25 m/s using a f = 100 mm objective obtained with a new scanning system and scanner tuning maintaining a precision of about 5 µ m. Further it will be shown that, especially for short line lengths, the machining time can be minimized by choosing the proper speed which has not to be the maximum one .
ZnO one of the promising candidates for ultraviolet (UV) emitting devices, such as UV light emitting diodes and UV lasers. In addition, ZnO nano/ microstructures have attracted a considerable attention as building blocks because of their high crystalline quality and unique structures. Among of them, symmetrical ZnO nano/microcrystals can serve as good resonance cavities without additional mirrors due to the high refractive index of ZnO.
In our study, we have succeeded in synthesizing ZnO nano/microspheres by a simple atmospheric laser ablation method, and demonstrated UV WGM lasing from the spheres. In this synthesizing method, a rapid melting and solidifying process may effective for doping impurities into ZnO. In this study, we synthesized doped ZnO spherical crystals using MgO contained targets, and blue-shift of UV WGM lasing peaks from the Mg-doped ZnO microsphere was observed. In this paper, structural and optical properties of the spherical ZnO microcrystals are reported.
9735-37, Session 12
(Invited
Paper)
Rainer Kling, Marc Faucon, Girolamo Mincuzzi, ALPhANOV
(France)
Nanometric topographies on surfaces provide specific functions in nature like the well-known lotus effect. To reproduce these topographies with laser technologies is a big challenge but represents a key enabling technology for industrial commercialisation. High average power ultrafast lasers are a crucial element to obtain high throughput fabrication. In this presentation the creation mechanisms of LIPSS are introduced. Potentials and limitations to master the nanoscale will be discussed with examples of technical applications of surface functions covering decoration, tribology and antireflection.
9735-38, Session 12
Beat Jaeggi, Beat Neuenschwander, Markus Zimmermann,
Berner Fachhochschule Technik und Informatik
(Switzerland); Markus Zecherle, Ernst Wilhelm Boeckler,
SCANLAB AG (Germany)
High accuracy, quality and throughput are key factors in laser micro machining. To obtain these goals the ablation process, the machining strategy and the scanning device have to be optimized. The precision is influenced by the accuracy of the galvo scanner and can further be enhanced by synchronizing the movement of the mirrors with the laser pulse train. To maintain a high machining quality i.e. minimum surface roughness, the pulse to pulse distance has also to be optimized. Highest ablation efficiency is obtained by choosing the proper laser peak fluence together with highest specific removal rate. The throughput can now be enhanced by simultaneously increasing the average power, the repetition rate as well as the scanning speed to preserve the fluence and the pulse to pulse distance. Therefore a high scanning speed is of essential importance.
9735-39, Session 12
Jie Zhang, Sha Tao, Brian Wang, Jay Zhao, Advanced
Optowave Corp (United States)
From an academic point of view, laser material processing with short
& ultrafast pulses, including nanosecond (ns), picosecond (ps) and femtosecond (fs), has been well-studied and well-understood. There are very clear processing solutions, such as using what type laser for what type materials to achieve the best quality; however, for the applications within manufacturing, it is not so simple because of their impact on throughput & cost. Quality is no longer the most important request. Instead, throughput and cost have become more critical. Good processing solutions have to meet both quality and throughput targets. According to laser market value, the shorter the laser pulse width, the higher the laser price is. Thus, it is important to provide the most suitable and affordable solution to users by choosing the right laser sources (wavelength, pulse width) based on the properties of the material to be processed.
In this paper, processing of several industry-favored key materials of metal, semiconductor, glass, ceramic and polymer have been systematically studied using different lasers including ns, sub-ns, ps and sub-ps pulses.
The quality and speed are based on the industry user’s requirements. The studies include both theoretical modeling and experiments. In simulations,
1D model was employed to simulate ns and sub-ns laser ablation and the two-temperature model is employed to simulate ps, the sub-ps laser ablation process to understand the underlying physical mechanism, and predict the ablation rates. The model was verified by a classic laser ablation experiment and then applied to other materials. In the experiments, a full scope of laser ablation-based cutting, drilling, and patterning of different materials with different pulse widths were carried out. Our studies show that with optimized processing conditions, appropriate beam delivery system and theright laser source, it is feasible to achieve good quality and high throughput by using affordable lasers.
9735-40, Session 13
(Invited
Paper)
Andres F . Lasagni, Fraunhofer IWS Dresden (Germany) and TU Dresden (Germany); Tim Kunze, Matthias Bieda,
Fraunhofer IWS Dresden (Germany); Denise Günther,
TU Dresden (Germany) and Fraunhofer IWS Dresden
(Germany); Anne Gärtner, Technische Universität Dresden
(Germany); Valentin Lang, TU Dresden (Germany) and
Fraunhofer IWS Dresden (Germany); Andreas Rank, TU
Dresden (Germany); Teja Roch, Fraunhofer IWS Dresden
(Germany) and TU Dresden (Germany)
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Conference 9735: Laser Applications in Microelectronic and
Optoelectronic Manufacturing (LAMOM) XXI
Smart surfaces are a source of innovation in the 21st Century. Potential aplications can be found in a wide range of fields where improved optical, mechanical or biological properties can enhance the functions of products.
In the last years, laser based fabrication methods have significantly improved their potential to functionalize surfaces based on the strong development of ultrashort pulsed laser systems as well as due to the higher available laser power. Laser surface processing excels over mechanical, chemical, and electric discharge texturing because it allows localized modifications with a large degree of control over the shape and size of the features that are formed. Furthermore, a greater range of sizes can be produced. In addition, it is generally cheaper than e-beam texturing and more flexible, because it does not require vacuum. Various textures can be accurately produced by controlling processing parameters such as beam intensity, spatial and temporal profile, wavelength, and processing environment (background gas or liquid). On the other hand, the fabrication of surface patterns with feature sizes of 1 to 10 µ m requires significant efforts to assure high quality and homogeneity over large areas. In this study, the fabrication of spatially ordered structures using Direct Laser
Interference Patterning (DLIP) is demonstrated. Different application examples, including the processing of 2D and 3D surfaces are introduced and applied to improve the surface properties of polymers, metals and coatings. Initial investigations of large area structuring of stamps for 2D and roll-to-roll (R2R) processing are also discussed.
9735-42, Session 13
Tao Zhang, Mahder Tewolde, Stony Brook Univ . (United
States); Ki-Hoon Kim, Dong-Min Seo, Stony Brook Univ
(United States); Jon P . Longtin, David J . Hwang, Stony
Brook Univ . (United States)
In this study, we will present recent progress in the laser-assisted manufacturing of thermal energy devices that require suppressed thermal transport characteristics yet maintaining other functionalities such as electronic transport or mechanical strength. Examples of such devices to be demonstrated include thermoelectric generator or insulating materials.
To this end, it will be shown that a hybrid additive and subtractive manufacturing approaches are significantly facilitated by unique processing capabilities of lasers under both thermal and non-thermal mechanisms, in a highly controllable fashion. On the basis of thermal, electrical, mechanical and morphological characterization of the laser-manufactured devices in conjunction with theoretical consideration, strategies for the optimal thermal energy device fabrication will be discussed.
9735-41, Session 13
Beat Neuenschwander, Markus Zimmermann, Beat
Jaeggi, Berner Fachhochschule Technik und Informatik
(Switzerland)
Beside high precision and high surface quality also power scaling represents a key factor for successful transfer of ultra-short pulsed laser micromachining to industrial applications. To maintain efficiency and quality machining should be done at the optimum fluence and a pulse to pulse distance of about half of the spot radius. In former experiments power scaling was demonstrated for different steel grades with a polygon line scanner up to an average power of 40 W with a spot radius of about 30
µ m at a repetition rate up to 8 MHz. Due to the higher threshold fluence this set up could not be used for copper and scaling was demonstrated with a galvo scanner and a spot radius of 16 µ m only. Hence the maximum marking speed of about 10 m/s limited the average power to about 10 W at a repetition rate of 1 MHz.
Higher average power becomes accessible with a new laser system having twice the average power and the existing polygon line scanner or with a new galvo scanner, offering higher speeds, and the existing laser system.
With these systems the power scaling experiments on steel and copper will be continued and other materials will be investigated as well to check if heat accumulation and/or shielding effects take place and will influence the removal rate and the machining quality.
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9736-1, Session 1
(Invited Paper)
Ville Hevonkorpi, Heidi Lundén, Antti Määttänen,
Primoceler, Inc . (Finland)
The use of glass in semiconductor industry has been growing the past years and the use is estimated to grow considerably during the coming years.
For efficient manufacturing, especially when using ultra-thin wafers, novel bonding technologies are needed. In this paper, a laser assisted additive free glass-glass welding technology is presented. Furthermore, the use of laser assisted welding in temporary bonding and in manufacturing of hermetic packages for optical sensors is investigated. The reliability of the weld and the robustness of the process is verified by moisture resistance and temperature cycling testing. A large quantity, one hundred samples, was selected to the moisture resistance testing to define the repeatability of the welding process. Two glass types used commonly in manufacturing consumer products and medical devices were selected. These glass types are Borofloat 33 and D263T.
Glass-glass welding proved to be a reliable bonding process offering a non-outgassing, room temperature bonding. In addition, it was verified that the weld is hermetic having a good resistance to thermal cycling. No changes in the welding seam were discovered during moisture resistance or temperature cycling tests.
9736-3, Session 1
Frank Gaebler, Coherent (Deutschland) GmbH (Germany);
Joris van Nunen, Andrew Held, Coherent Inc (United
States)
Ultrafast laser machining is gaining traction as it offers very precise processing of materials with low thermal impact. Large-scale industrial ultrafast laser applications show that the market can be divided in various sub segments. One set of applications demand low power, compact footprint and are extremely sensitive to the laser price whilst still demanding 10ps or shorter laser pulses. A second set of applications are very power hungry and only become economically feasible for large scale deployments at power levels in the 100W class. There is a growing demand for applications requiring fs-laser pulses. In our presentation we would like to describe these sub segments by using selected applications from the automotive and electronics industry e.g. drilling of gas/diesel injection nozzles, dicing of LED substrates and structuring of battery foils for xEV vehicles. We close the presentation with an outlook to micromachining applications e.g. µ via hole drilling and foil processing with unique new CO lasers emitting 5 µ m laser wavelength.
9736-2, Session 1
(Invited Paper)
Javier Solis, Instituto de Óptica “Daza de Valdés” (Spain)
Although compositional changes induced by fs-laser irradiation of glass have been studied by more than ten years, only recently it has been shown that these changes can be efficiently used to modify the local refractive index of glasses with a large degree of controllability. We have shown that fs-laser irradiation at high repetition rate in phosphate glasses with lanthanum and potassium oxides acting as glass modifiers leads to local element redistribution, and the formation of efficient passive and active waveguides with a refractive index contrast >10E(-2). The local refractive index changes, in this case, are due to the cross migration of La and K species, La being the element controlling the local refractive index of the structures. A similar mechanism has been also observed in a different glass family (tellurites). The feasibility of inducing the controlled migration of ions by fs-laser irradiation opens up new prospects for fabricating efficient integrated optical devices inside glasses by direct femtosecond laser writing, overcoming the refractive index contrast limitations associated to more conventional glass modification mechanisms. We will review our results regarding fs-laser induced ion migration for photonics applications with special emphasis in the control that can be exerted over their characteristics (size, refractive index change and local composition) as well on the performance of the so generated structures as passive and active waveguides and lasers. Results regarding the use of in-situ plasma emission imaging during the writing process will also be presented in order to discuss the origin of the ion migration phenomenon.
9736-4, Session 1
Amin Abdolvand, Univ . of Dundee (United Kingdom)
Direct joining techniques of glass with a focused ultra-short (femtosecond or picosecond) pulsed laser beam have recently been reported. In these studies, by focusing the ultra-short laser pulses at the interface between the glass substrates, the nonlinear absorption of the beam has been exploited and glass joint strength of 14.9 MPa was reported. However, there are a number of shortcomings associated with this technique. The process requires a lens objective of high numerical aperture, typically in the range of 0.4 - 0.65. This leads to a poor working distance and welding depth, and ultimately restricts the welding efficiency and the processing speed. It also imposes strict requirements on the surface quality of the work pieces - currently within ?/4. The above constitutes a serious challenge for widespread adoption of this technique by industry.
We present rapid and strong joining of clear glass to glass containing randomly distributed embedded spherical silver nanoparticles upon nanosecond pulsed laser irradiation at 532 nm. The embedded metallic nanoparticle were (30 nm in diameter) were embedded in a thin surface layer the nano-composite. A joint strength of 12.5 MPa was achieved for a very low laser fluence (< 0.2 J/cm2) and scanning speed of 10 mm/s. The bonding mechanism is discussed in terms of absorption of the laser energy by nanoparticles and the transfer of the accumulated localised heat to the surrounding glass leading to the local melting and formation of a strong bond.
9736-5, Session 1
Amin Abdolvand, William A . Gillespie, Mateusz A . Tyrk,
Svetlana A . Zolotovskaya, Univ . of Dundee (United
Kingdom)
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9736-6, Session 2
Conference 9736:
Laser-based Micro- and Nanoprocessing X
Dielectrics containing metal nanoparticles comprise a promising class of materials for many applications in optoelectronics. These nanocomposites are of interest due to their unique linear and nonlinear optical properties.
These properties are dominated by the strong surface plasmon resonances of the metal nanoparticles. The spectral position and shape of the SPRs can be designed within a wide spectral range throughout the visible and near-infrared spectra by choice of the metal and the dielectric matrix, plus manipulation of nanoparticle size, shape, and spatial distribution.
Radially and azimuthally polarized picosecond (~10 ps) pulsed laser irradiation at 532 nm wavelength led to the permanent reshaping of spherical silver nanoparticles (of 40 nm) embedded in a thin layer of sodalime glass. We demonstrate formation of the Ag nano-ellipsoids and analyze their orientation within the irradiated areas as a result of the polarization state of the incident beam. The fabricated nanostructures are characterized using Second Harmonic Generation from the elliptical nanoparticles for determination of the shape and position of nanoparticles within the modified areas.
The presented reshaping method adds a versatile technique to structural manipulations of metal-glass nanocomposites at large scale. It paves the way for nanoparticle shape modification in terms of future new experiments that could be performed with different laser polarizations in order to achieve more complicated nanoparticle structures. This method can lead to nanoengineering of novel optical materials and indeed sophisticated storage of information in this class of nanomaterials.
(Invited Paper)
Mangirdas Malinauskas, Sima Rek?tyt?, Albertas
?ukauskas, Simas Butkus, Vilnius Univ . (Lithuania); Saulius
Juodkazis, Swinburne Univ . of Technology (Australia)
[6] M. Malinauskas et al., Micromachines, 5(4), 839 (2014).
[7] J. Maciulaitis et al., Biofabrication, 7, 015015 (2015).
9736-7, Session 2
Arkadiusz J . Antonczak, Bogusz D . Stepak, Krzysztof M .
Abramski, Wroclaw Univ . of Technology (Poland)
This paper presents a method that enables fast and low-cost fabrication of microchannels with oval cross-section. The procedure is based on formation of a concave meniscus at the interface between an initially cured PDMS and a polymeric mould fabricated using excimer laser. In this technique, the mould is not filled with uncured PDMS. The replica is formed by expanding gas trapped within the structures of the mould during thermal curing. A second shaping factor is connected with surface phenomena at the interface between the mould, gas and partially cured PDMS. The final shape of the meniscus is determined when the PDMS reaches the high cure extent. The microchannels with oval cross-section are obtained by using a completely cured PDMS replica as a mould in an analogical second fabrication step. As a result an all-in-PDMS chip can be produced. The cross-section of channels can be controlled by changing the curing conditions. We investigated the influence of the initial PDMS curing time and pressure during final curing on the geometry of the created microchannels. The fabricated microstructures are characterized by constant depth and high quality of the surface.
9736-8, Session 2
Juliana M . P . Almeida, Emerson C . Barbano, Lino Misoguti,
Univ . de São Paulo (Brazil); Craig B . Arnold, Princeton Univ .
(United States); Cleber R . Mendonça, Univ . de São Paulo
(Brazil)
Today ultrafast laser based micro- and nano-processing technologies enable the most advanced material manufacturing options. It is proved in terms of spatial resolution, fabrication throughput, choice of materials, and
3D structuring capability. Tightly focused femtosecond pulses empower determination of light-matter interaction mechanisms, thus creating a potential to choose the type of material modification within ultra-confined
3D space. Selectivity is the key performance indicator of femtosecond direct laser writing opening the prospect to tune the physical (mechanical stiffness, refractive index), chemical (reactivity), biological (biocompatibility, resorption) material properties. This can be employed for 4D optical printing, where besides the 3 space coordinates, the material deposition (or modification of its properties) can be distinctively controlled.
Here we report on recent advances in fs-DLW based material processing
[1,2], specifically:
- Study of lithography mechanisms, mainly the influence of light’s polarization to spatial resolution [3];
- Tuning the refractive index in 3D lithography towards GRIN free-form microoptics [4];
- Reversible deformations of composite material polymeric microstructures in fluids [5];
- Light filament assisted ablation processing of fused filament fabrication manufactured 3D objects [6];
- Pre-clinical study of SZ2080 microporous scaffolds for cartilage tissue engineering [7].
[1] M. Malinauskas et al., Phys. Rep. 533(1), 1 (2013).
[2] M. Malinauskas et al., Light: Sci. Appl. to be published, (2015).
[3] T. Jonavicius et al., submitted.
[4] A. Zukauskas et al., under review.
[5] S. Rekstyte et al., in preparation.
The large interest in nonlinear optical materials has been motivated by their potential use in the fabrication of all-optical devices. Arsenic trisulfide is a chalcogenide glass that has received special attention due to its high refractive index and transparency over MIR region. Moreover, As2S3 presents a variety of photosensible properties, including photocrystallization and photodarkening, which potentiates its applications in infrared technologies
[1]. Recently, we have developed a single-step synthesis of silver sulfide nanocrystals (Ag2S-NCs) in As2S3 [2]. Ag2S is also a semiconductor, but when synthetized at the nanometer scale can be used as NIR emitters, sensitizers for solar cells and substrates for SERS.
In this work, we have encompassed the features of As2S3 and Ag2S-NCs in a waveguide, produced by femtosecond laser micromachining. This technique enables to write complex geometry, which is an important step towards integrated systems. At first, thin films were produced on glass substrates. Then, femtosecond laser micromachining (800 nm, 50 fs, 5 MHz) was employed to obtain the threshold energy for inducing modification, being 0.19 ± 0.02 nJ. Adjusting the fabrication conditions we have been able to write slab waveguides. In addition, the nonlinear optical properties of pure As2S3 and Ag2S-NCs doped waveguides have been investigated at the ultra-short pulses regime. Because the material is thin (~ 500 nm), a recently developed method, called nonlinear ellipse rotation, was applied to obtain the nonlinear index of refraction [3]. The nonlinear refractive index of the sample was determined to be two orders of magnitude higher than fused silica.
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Conference 9736:
Laser-based Micro- and Nanoprocessing X
References:
[1] A. Zakery, and S. R. Elliott, “Optical properties and applications of chalcogenide glasses: a review,” Journal of Non-Crystalline Solids 330, 1-12
(2003).
[2] J. M. P. Almeida, C. Lu, C. R. Mendonça, and C. B. Arnold, “Single-step synthesis of silver sulfide nanocrystals in arsenic trisulfide,” Optical Materials
Express 5, 1815-1821 (2015).
[3] M. L. Miguez, E. C. Barbano, S. C. Zilio, and L. Misoguti, “Accurate measurement of nonlinear ellipse rotation using a phase-sensitive method,”
Optics Express 22, 25530-25538 (2014).
damage by local heating is reduced to well below a few microns. In view of these outstanding characteristics of lasers, it is very surprising that sample preparation for microstructure diagnostics did not derive the advantages from laser micro-machining. microPREP, is a new laser-micromachining tool developed by 3D-Micromac capable of making fast, clean, and efficient laser ablation available for the preparation of samples for transmission electron microscopy (TEM). The workflow follows a three-stage approach. First, a supporting basic structure is cut from the feedstock. Second, the supported structure is laser-thinned down to a few microns and third, the supported and laser-thinned structure is thinned using a focused ion beam or an ion broad beam.
The examples presented in this paper support this approach and show it is ready to be applied in different areas of microstructure diagnostics and has very high potential for failure diagnostics.
9736-9, Session 2
Ivan I . Bobrinetskiy, AIMEN - Asociación de Investigación
Metalúrgica del Noroeste (Spain); Alexey V Emelianov,
National Research University of Electronic Technology
(Russian Federation); Nerea Otero, Pablo Romero, AIMEN
- Asociación de Investigación Metalúrgica del Noroeste
(Spain)
Carbon nanomaterials are the most promising objects for advanced electronic applications, due to its extraordinary chemical and physical properties. Nonetheless, after more than two decades of intensive research, the application of carbon-based nanostructures in real electronic and optoelectronic devices is still a big challenge due to lack of scalable integration in microelectronic manufacturing. The laser processing can be the most attractive tools for graphene device manufacturing because of a huge variety of results of graphene lattice and pulsed laser irradiation interaction: functionalization, oxidation, reduction, etching and ablation, growth, etc. with resolution down to the nanoscale. The idea of totally mask-less processing of graphene and carbon nanotube films by laser pulses is attractive to reduce costs, improve flexibility, and reduce alignment operations, by producing fully functional devices in single direct-write operations. In this paper, a picoseconds laser with a wavelength of 515 nm and pulse width of 30 ps is used to pattern carbon nanostructures in two ways: ablation and chemical functionalization. The light absorption leads to thermal ablation of graphene and carbon nanotube film under the fluence
60-90 J/cm2 with scanning speed up to 2 m/s. Just below the ablation energy the two-photon absorption leads to adding functional groups to carbon lattice changing optical properties of graphene. This opens the way for both geometrical configuration of carbon based nanostructures and physical and chemical properties alteration in one process by direct laser writing methods.
9736-11, Session 3
Akira Watanabe, Jinguang Cai, Tohoku Univ . (Japan); Gang
Qin, Lidan Fan, Henan Polytechnic Univ . (China)
Recent progress in printed electronics is based on the development of various kinds of nanomaterials in the past decade. Many types of silver nanoparticle inks have been proposed for printing electric wires. Because of the strong risk of the silver migration in an electronic circuit, copper wiring materials are indispensable for recent printed electronics. However, one of the problems in the application of the copper nanoparticles as a printing material is the rapid surface oxidation in air. In this work, we report the laser direct writing using a copper nanoparticle ink to prepare a conductive copper micropattern. The rapid laser sintering process reduced the oxidation of the copper nanoparticle surface and enabled the formation of a conductive micropattern at room temperature in air. A high spatial resolution is also advantage of the laser direct writing method. Recently, the fabrication process of a copper grid structure is under intense investigation toward indium tin oxide (ITO)-free devises. Transparent conductive electrode is one of the essential components in printable electronics devices. A low-cost, indium-free, and crack-tolerant electrode is of great interest in the printed electronics in the field of touch screen displays. In the manufacturing processes, the patterning of metal grid structure is responsible for more than 50% of touch screen production cost. The laser direct writing using a copper nanoparticle ink has a possibility to develop an efficient patterning process for a copper grid structure. Various kinds of copper grid structures were prepared and then the conductivities and transparency were discussed.
9736-10, Session 3
(Invited Paper)
Uwe Wagner, ED Micromac AG (Germany); Tino Petsch,
3D-Micromac AG (Germany); Michael Krause, Thomas
Höche, Fraunhofer Institute for Mechanics of Materials
(Germany)
Over the past fifty year, lasers have found many, often groundbreaking applications in science and technology. The most important features of lasers are that photons are inherently free of contamination, extremely high energy densities can be focused in very small areas and the laser beam can be precisely positioned using deflection mirrors. By reducing pulse lengths from a few nanoseconds down to the picosecond or femtosecond range, material ablation is becoming increasingly “athermal”, i.e. structure
9736-12, Session 3
Joseph T . Hillman, Y . Sukhman, D . Miller, M . Oropeza, C .
Risser, Universal Laser Systems, Inc . (United States)
Laser processing is a versatile method for creating micrometer scale features for flexible electronic circuits. Selective laser ablation has been used to create vias through polyimide insulating layers to make electrical contact with underlying copper traces. The 10.6 µ m wavelength light from a CO2 laser is absorbed efficiently by the polyimide, but is reflected by the copper surface making the via formation process completely selective. The process is enhanced by combining the CO2 laser beam with a 1.062 µ m laser beam from an Yb-doped fiber laser. This multiwave hybrid laser beam provides a cleaner copper surface, while maintaining the selectivity of the via formation process.
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Multiwave laser processing also serves as an efficient tool for rapid prototyping. Conductive materials such as silver or carbon can be selectively ablated from an insulating substrate substrate like PET using a 1.062 µ m wavelength. This wavelength is absorbed by the conductive layer causing it to vaporize. However the polymer substrate is transparent to this wavelength, allowing the conductor to be patterned with no damage to the substrate. Switching to a 9.3 µ m CO2 laser enables efficient marking of the PET substrate due to the strong absorption line at this wavelength.
Finally a high power 10.6 µ m CO2 laser is used to cut the finished circuit to the desired shape. In this way, three essential prototyping steps that each require a different laser wavelength can be completed on a single laser system.
9736-14, Session 3
Conference 9736:
Laser-based Micro- and Nanoprocessing X
µ
Klaus Stolberg, Susanna Friedel, JENOPTIK Laser GmbH
(Germany) methods: laser ablation, plasma etching, chemical oxidation, and thermal rescaling of polymers are compared in terms of suitability for surface enhanced Raman sensing/spectroscopy (SERS). As thickness of gold is increasing from tens to hundreds of nanometers an additional surface nanogap/groove pattern develops and increases SERS intensity. Benchmarking of different substrates was carried out by measureing SERS using a selfassembled layer of thiophenol on the surface of gold. Mechanisms of SERS enhancement by the electromagnetic and chemical factors are discussed together with strategies to achieve higher SERS sensitivity and selectivity in sensor applications.
Randomness of the surface pattern is shown to be an important parameter for the additional 2-4 factor in SERS enhancement. In the case of transparent SERS samples with nano-islands of gold at coverage close to the threshold of gold film percolation threshold, an additional enhancement proportional to the refractive index square, n^2 is demonstrated for illumination from the substrate side (n is the refractive index of the substrate). It is shown that dark field imaging of SERS substrates clearly shows the optimum wavelength for excitation of Raman scattering.
Microfeatures in mechanical parts can be generated by variety of
“traditional” technologies like EDM, chemical etching or micromilling.
All of them have limitations with respect of feature size, productivity or even chemical reactivity. Since a lot of years there are efforts to use the advantages of laser processing: small feature size can be reached by laser spot size in the µ m range; productivity can be enhanced by laser power scaling or beam shaping and lack of mechanical contact prevents introduction of foreign materials or stress in the process. Furtheron the laser processability does not depend on mechanical, chemical, electrical behavior like other technologies do. Unfortunately cw and pulsed lasers down to ns pulse duration show undesired thermal effects.
We demonstrate steep wall angles by the application of a trepanning optics and together with a 10 W femtosecond laser laser cutting, drilling and engraving of 100 to 500 µ m thick metals like Cu-alloy, stainless steel, titanium and tantalum can be achieved in a non-thermal melt-free process.
Particularly for thin materials, this is advantageous compared to traditional laser fusion cutting, because in this thermal process heat accumulation usually causes mechanical distortion or edge melting as well as material bending caused by pressure of the processing gas.
The combination of beam deflection in trepanning optics and sample motion allowed us to work in a special “laser milling mode” with rotating beam. Zero degree taper angle as well as positive or negative tapers can be achieved. We compare the trepanning results with the results of fine cutting optics. We also demonstrate contour cutting of sophisticated materials like ceramics and polymers.
9736-16, Session 4
Nerea Otero, Pablo M . Romero, Paula Rico, AIMEN -
Asociación de Investigación Metalúrgica del Noroeste
(Spain); Jose M . Saiz-Jabardo, Pablo Fariñas, Univ . da
Coruña (Spain)
Nucleate boiling is a heat transfer mechanism which is characterized by high heat transfer rates, adequate for applications where high power density is present. Though exhaustively investigated during the last decades, the physical mechanisms have not yet being adequately defined. One of the most important aspects is the effect of the heating surface microstructure on the rate of heat transfer and its interaction with the boiling liquid.
The present experimental research has been focused in the development by laser technologies of surface microstructures for developing heat transfer enhanced surfaces. Different laser sources were selected, to modify the surface structure of stainless steel, copper and brass. With the main aim of understanding the effect of the surface finishing on the nucleate boiling, the generated surfaces have been analyzed with confocal microscopy, contact angle and surface tension measurements, in order to relate the surface finishing and its effect on the nucleate boiling heat transfer. Additionally, the effect of the laser treatment on the surface microstructure has been studied by scanning electron microscopy with energy dispersive X ray spectroscopy.
9736-13, Session 4
(Invited Paper)
Chunlei Guo, Univ . of Rochester (United States)
No Abstract Available
9736-15, Session 4
(Invited Paper)
Saulius Juodkazis, Swinburne Univ . of Technology
(Australia)
Properties of the gold-coated nanotextured surfaces prepared by different
9736-17, Session 4
Abel Gil Villalba, Chen Xie, Roland Salut, Luca Fufaro,
Remo Giust, Maxime Jacquot, Pierre-Ambroise Lacourt,
John M . Dudley, François Courvoisier, FEMTO-ST (France)
Graphene is a major material for next-generation electronics and optoelectronics. Fast patterning technologies are needed, that can operate in the sub-micron regime and over areas of square-meter scale. Ultrafast laser ablation is ideally suited since the process is single step and contactfree.
We investigate the single shot ablation of single layer-CVD graphene by ultrafast lasers. We have developed a novel technique to characterize the fluence for ablation threshold that is valid at nanometric scale and allows for investigating the potential variations with crater diameter.
We use a 3-wave interference beam pattern that generates approx. 40 craters simultaneously. The numerical correlation of SEM image of the crater
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Conference 9736:
Laser-based Micro- and Nanoprocessing X pattern and of the fluence pattern provides insights in the ablation process.
We extract ablation threshold fluence for pulse durations between 120 fs and 3 ps. We observe a constant threshold for ablation for all scales but we measured a strong decrease of the ablation probability for crater diameters below 1 µ m. Yet the decrease of the probability of the presence of defects can explain this drop, we highlight the importance of free-electron diffusion in graphene. Indeed, graphene has extremely high electron mobility: the diffusion of free-electrons competes with the confinement of laser energy deposition that is necessary for ablation at nanometric scale.
9736-51, Session PTue
Matthias Roth, TU Dresden (Germany); Jörg Heber,
Fraunhofer-Institut für Photonische Mikrosysteme
(Germany); Klaus Janschek, TU Dresden (Germany)
9736-19, Session 4
Krystian L . Wlodarczyk, Heriot-Watt Univ . (United
Kingdom); Marcus Ardron, Nick J . Weston, Renishaw plc
(United Kingdom); Duncan P . Hand, Heriot-Watt Univ .
(United Kingdom)
We present a laser-based process for the generation of phase holographic structures directly onto the surface of metals. This process uses 35ns laser pulses of wavelength 355nm to generate optically-smooth surface deformations on a metal. The laser-induced surface deformations (LISDs) are produced by either localised laser melting or the combination of melting and evaporation. The geometry (shape and dimension) of the LISDs depends on the laser processing parameters, such as pulse energy and the number of laser pulses in a spot, as well as on the chemical composition of a metal and the spatial intensity distribution of the laser beam used in the process. In this paper, we will explain the mechanism of the LISDs formation on various metals, such as 304-grade stainless steel, 99% pure nickel and nickel-chromium Inconel® alloys. In addition, we provide information about the design and fabrication process of holographic structures, including issues we are currently facing. Finally, it will be demonstrated that the laser-generated holographic structures can be used as robust marks for identification and traceability of high value metal components and products.
A generic optical 4f-setup, consisting of two lenses and two modulators placed in the consecutive focal planes, forms the basis for several beam shaping approaches for intensity modulation. The primary interest of this study lies in light-efficient generation of patterns or multiple spots in the image plane by means of pure phase modulating elements.
4f approaches share the property that due to the one-to-one relationships between output intensity and input phase, no online calculation is needed.
The resulting low computational complexity is offering a major advantage of 4f-methods compared to the widely used Fourier Holography and makes them attractive candidates for real-time applications. Increasing availability of fast phase modulators, e.g. on MEMS basis, demands for an evaluation of the performance of these concepts.
Our aim is to assess the applicability of these 4f methods to high-power applications. We present a system level trade-off for several variants of
4f intensity shaping by phase modulation. It includes micro mirror based phase manipulation combined with amplitude masking in the Fourier plane,
Generalized Phase Contrast, a generalization of Zernike’s phase contrast microscopy relying on pure phase modulation in both image and Fourier plane, and phase-only correlation, a technique originating from signal processing likewise employing two programmable phase filters.
This paper compares these concepts using a generic setup and derives figures of merit for energy efficiency, pattern homogeneity, pattern image quality, maximum output intensity and flexibility with respect to the displayable pattern. Numerical simulations illustrate our findings.
9736-50, Session PTue
Xianheng Yang, Guoying Feng, Shouhuan Zhou, Sichuan
Univ . (China)
A random lasing emission based on microporous surface of Cr2+:ZnSe crystal was demonstrated. The microporous surface was prepared by femtosecond pulsed laser ablation in high vacuum (below 5?10-4 Pa).
The scanning electron microscope results show that there are a mass of micropores with an average size of ~13 ?m and smaller ones with ~1.2 ?m on the surface of Cr2+:ZnSe crystal. The adjacent micropore spacing of the smaller micropores ranges from 1 ?m to 5 ?m. The X-ray diffraction patterns reveal that the crystallization of Cr2+:ZnSe changes little after pulsed laser ablation. Under 1750 nm excitation of Nd:YAG (355 nm) pumped optical parametric oscillator, a random lasing emission with center wavelength of
2350 nm and laser-like threshold of 0.3 mJ/pulse is observed. The emission lifetime of 2350 nm laser reduces from 800 ns to 30 ns as the pump energy increases above threshold.
9736-52, Session PTue
Takahiro Nakamura, Koki Omachi, Shinichi Sato, Tohoku
Univ . (Japan)
Direct writing techniques have become a worldwide topic due to the capability of direct formation of desired 2D and 3D structures of various materials. However, there are still difficulties to form fine structures, because the minimum pixel size is limited to micrometer order. Laser-induced forward transfer (LIFT) can be an alternative route for the fabrication of submicron-scale structures. The size of transferred fraction of the carrier film by LIFT can be decreased to sub-micron by controlling laser energy and focal spot size of applied laser beam on the carrier film. In the present study, we demonstrated the direct formation of submicron structures by
LIFT in different laser fluence conditions. A metal Cr film, which was formed on a transparent cover glass substrate with the thickness of 30 nm as a carrier, was placed directly on a Si single crystal substrate. Single shot of femtosecond laser pulse (lambda = 800 nm, 100 fs) was focused by an objective lens (?100, NA=0.8) and irradiated on the Cr carrier film from the backside of the transparent glass substrate. Although multiple deposition of Cr particles with wide size distribution were observed on the Si substrate surface for the laser energy higher than 5.5 nJ, spherical shaped Cr particles with the size of 100 nm were transferred at the exact position of the substrate on demand with the laser energy of 5.0 nJ. Effect of the intensity distribution at the cross section of introduced laser beam on the LIFT was also examined.
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Conference 9736:
Laser-based Micro- and Nanoprocessing X
9736-53, Session PTue
Aoi Matsumoto, Takayuki Tamaki, Shinichi Enoki, Nara
National College of Technology (Japan); Keisuke Yahata,
Mitsuboshi Diamond Industrial Co . ,LTD . (Japan); Etsuji
Ohmura, Osaka Univ . (Japan)
9736-55, Session PTue
Pierre Lorenz, Leibniz-Institut für
Oberflächenmodifizierung e .V . (Germany); Joachim
Zajadazc, Leibniz-Institut für Oberflächenmodifizierung eV (Germany); Martin Ehrhardt, Lukas Bayer, Klaus-Peter
Zimmer, Leibniz-Institut für Oberflächenmodifizierung e .V .
(Germany)
Two wavelengths laser microprocessing system has been developed, where femtosecond laser and CO2 laser beam are irradiated at the same time and wide-area processing can be obtained. The target of this research is to establish a heat transfer analysis model for this system.
First we simulate the heating phenomenon inside BK7 glass (OHARA,
S-BSL7, 30?5?0.67 mm) with either femtosecond or CO2 laser alone by the finite element method, using ANSYS mechanical APDL.
The femtosecond laser has a wavelength of 1.064 µ m and a repetition frequency of 1 MHz.
Because we consider the heating phenomenon that continues for several seconds, the femtosecond laser could be assumed as continuous wave source.
When the femtosecond laser is assumed to be absorbed in a cone-shaped region, the temperature distribution got closer to experimental results compared to the cases of rod- or cylinder- shaped absorption region.
Next we simulate the heating phenomenon with a CO2 laser whose wavelength is 10.6 µ m.
The beam size of CO2 laser is determined from the experimental results and the heating with a CO2 laser is modeled as surface heat source.
By the analysis results, the CO2 laser beam is considered to be heat source.
9736-54, Session PTue
Anton Schmailzl, Sebastian Steger, Michael Dostalek,
Stefan Hierl, Ostbayerische Technische Hochschule
Regensburg (Germany)
Quasi-simultaneous laser transmission welding is a well-known joining process for thermoplastics and mainly used in automotive- and medicalindustry. For process control usually the so called set-path monitoring is used, where the weld is specified as “good” if the welding time is inside a defined confidence interval. However the detection of small-sized remaining gaps or thermal damaged zones is not possible. The analyzation of the weld seam temperature during welding offers the possibility to overcome this problem. In this approach a 3D-scanner is used instead of a scanner with flat-field optic. In spite of using a pyrometer at a certain spectrum beside the laser wavelength no color-corrected optic is needed in order to provide that laser- and detection-spot are coaxial. Experimental studies on polyethylene t-joints have shown that the signal-noise ratio is adequate, despite using a long working distance and a small optical aperture. The effects on temperature are studied for defects like gaps in the joining zone.
Therefore gaps with different geometries are milled into the samples. In case of producing housings for electronic-parts the effect of a bonding wire between the joining partners is also investigated. Both defects can be identified by a local temperature deviation even at a feed rate of several meters per second. Furthermore strategies for signal-processing are demonstrated. By this, a decision can be made whether defects are remaining or not. Consequently an online detection of local defects is possible, so that a dynamic process control is feasible.
Nanostructures have a widespread field of applications. The structuring of different dielectrics (fused silica, sapphire, and diamond) was studied, assisted by a nanosecond laser-induced self-organised molten molybdenum layer deformation process. At low laser fluence the irradiation of thin metal layers on dielectric surfaces results in a melting and nanostructuring process of the metal layer and partially of the dielectric surface. The resultant structures are dependent on the substrate and the laser parameters.
Furthermore, a subsequent high laser fluence treatment of the metal nanostructures results in different features: (i) pattern transfer, (ii) selforganized surface nanostructuring, and (iii) nanodrilling. (i) Pattern Transfer:
The irradiation of the pre-structured metal layer with high laser fluences allows the transfer of the lateral geometry of the metal nanostructures into the dielectric surface. (ii) Self-organized surface nanostructuring: The multi-pulse irradiation of the metal layer/dielectric system with moderate laser fluences results in a self-organized nanostructuring of the dielectric surface. (iii) Nanodrilling: The multi-pulse low laser fluence irradiation of the metal layer results in the formation of metal droplets and a further high fluence irradiation of the laser-generated metal droplets results in a stepwise evaporation of the metal and in a partial evaporation of the dielectrics and, finally, in the formation of cone-like holes. The features are different developed for the different substrates. The resultant structures were investigated by atomic force (AFM) and scanning electron microscopy
(SEM). The process was simulated and the simulation results were compared with experimental ones.
9736-56, Session PTue
Pedro Moreno Zarate, Instituto Tecnologico Superior de
Tepexi de Rodriguez (Mexico); Jesús del Hoyo Muñoz,
Instituto de Óptica “Daza de Valdés” (Spain); Juan
Antonio Vallés, Miguel Angel Rebolledo, Univ . de Zaragoza
(Spain); Jan Siegel, Javier Solis, Instituto de Óptica “Daza de Valdés” (Spain)
It has recently been shown that La-K cross migration induced by high rep. rate fs-laser writing in P-La-K glasses enables producing waveguides with a refractive index contrast above 10^(-2). The index modification is given by a local La enrichment in the guiding region. This mechanism has been shown to be controllable in terms of the size of the guiding regions and its refractive index. In this work we have analyzed the performance of structures produced by means of this mechanism as optical amplifiers and lasers in Er:Yb co—doped samples. It is important noticing that the guiding region is enriched by the same proportion in all the lanthanides contained in the glass. As a consequence the initial doping level (2wt.% Er2O3, 4wt.%
Yb2O3) is increased in the guiding region, enabling producing waveguides with controllable doping levels. Single mode waveguides with propagation losses as low as <0.1 dB/cm and total insertion losses of 1.0 dB at 1640 nm have been successfully produced. Higher refractive index contrast
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Conference 9736:
Laser-based Micro- and Nanoprocessing X waveguides support higher order modes, but insertion losses can be maintained as low as 1.2 dB preserving the active properties. Internal gains in the 8-10 dB have been observed for 24 mm long waveguides, leading to pumping thresholds as low as 50 mW and slope efficiencies above
20%. Modelling of these structures indicates that lasers with similar slope efficiencies and thresholds in the 10 mW range can be produced for optimal length waveguides. the feasibility of fs-laser waveguide production in L-threonine crystal by demonstrating its fabrication and characterization.
9736-57, Session PTue
Jianyong Chen, Richard M . Carter, Robert R . Thomson,
Duncan P . Hand, Heriot-Watt Univ . (United Kingdom)
9736-59, Session PTue
Maximilian G . Warhanek, Josquin Pfaff, Linus Meier,
Christian Walter, ETH Zürich (Switzerland); Konrad
Wegener, ETH Zürich (Switzerland) and Inspire AG
(Switzerland)
Techniques for joining materials, especially glass to dissimilar materials, while maintaining their surface and optical properties are essential for a wide range of industrial applications. Directly bringing two flat material surfaces into close contact and focussing the high peak power ultrafast laser onto the join allows for material bonding through nonlinear absorption.
Highly localized melting and rapid resolidification form firm bond at the two surfaces whilst avoiding significant heating of the surrounding material, which is important for joining materials with different thermal expansion coefficients.
Previous reports on ultrafast laser welding have identified a requirement for the surface separation gap to be less than 500nm in order to avoid cracking or ablation at the interface. For our investigation cylindrical lens and etched grooves methods of generating different surface separation to be welded were proposed and samples with controlled gaps were prepared to enable investigation of the relationship between the pre-existing gap with laser power, process speed and focal position when achieving a weld. Conditions of welding a large gap were revealed by welding a cylindrical lens and a plane piece of glass. Also discrete but more precise surface separations were generated with the etched grooves on a plane glass surface and five distinct types of welding patterns were observed over a range of different powers, focal positions and surface separations. By applying our optimized parameters, a surface separation of 3?m was successfully welded.
Mechanism of ultrafast pulses welding a gap was theoretically explained based on the cross-section views of welding gaps.
9736-58, Session PTue
Gustavo F . B . Almeida, Univ . de São Paulo (Brazil); José J .
Rodrigues Jr ., Univ . Federal de Sergipe (Brazil); Cleber R .
Mendonça, Univ . de São Paulo (Brazil)
Capability and advantages of laser ablation processes utilizing ultrashort pulses have been demonstrated in various applications of scientific and industrial nature. Of particular interest are applications that require high geometrical accuracy, excellent surface integrity and thus tolerate only a negligible heat affected zone in the processed area. In this context, this work presents a detailed study of the ablation characteristics of common ultrahard composite materials utilized in the cutting tool industry, namely polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PCBN). Due to the high hardness of these materials, conventional mechanical processing is time consuming and costly. Herein, laser ablation is an appealing alternative, since no process forces and no wear have to be taken into consideration. However, an industrially viable process requires a detailed understanding of the ablation characteristics of each material.
Therefore, the influence of various process parameters on material removal and processing quality at 10ps pulse duration are investigated for several
PCD and PCBN grades. This study examines the effect of different laser energy input distributions, such as pulse frequency, burst pulses and scanning strategies, on the processing conditions in deep cutting kerfs and the resulting geometrical accuracy as well as the quality of the generated surfaces. Based on these results, recommendations for efficient processing of such materials are derived.
9736-60, Session PTue
Ralph F . Delmdahl, Hans-Gerd Esser, Guido F . Bonati,
Coherent LaserSystems GmbH & Co . KG (Germany)
Over the years, direct laser writing using femtosecond laser has shown to be one of the most important techniques for material processing due to its versatility to modify material´s properties. One feature that receives great attention is the ability of changing the index of refraction of materials to produce three-dimensionally confined structures. The most common volumetric modification is the production of waveguides, that are of high demand for integrated optics. In this context, organic materials present interesting properties for photonics applications. For instance, L-threonine crystals have low index of refraction, wide window of transparency (250nm
– 1500nm), good second harmonic generation efficiency and low third order susceptibility. Such characteristics are desirable for nonlinear optical devices.
In this work, we used a Ti:sapphire laser that produces 50 fs pulse at 800 nm (5.2 MHz operation rate) to fabricate waveguides. Pulse energy of 20 nJ and scan speed of 20 ?m/s were find optimal parameters for waveguide fabrication. Homogeneous, 8 mm long waveguides with diameter on the order of approximately 1.0?m have been obtained. Waveguide coupling was performed using a He-Ne laser, with the aid of microscope objectives and a camera; a total loss of 24.8 dB/mm was measured. In conclusion, we showed
Progress in mass analysis applications such as laser ablation inductively coupled mass spectrometry of solid samples and ultraviolet photodissociation-induced sequencing of peptides and proteins is to a large extent driven by ultra-short wavelength excimer lasers at 193 nm. This paper will introduce the latest improvements achieved in compact excimer laser development and elaborate on the impact on mass spectrometry instrumentation. Various performance and lifetime measurements obtained in a long-term endurance test over the course of 18 months will be shown and discussed in detail in view of the laser source requirements of different mass spectrometry tasks. These sampling type applications are served by excimer lasers delivering pulsed 193 nm output of several Millijoules as well as fast repetition rates which are already approaching one Kilohertz. In order to open up the pathway from the laboratory to broader market industrial use, sufficient component lifetimes and long-term stable performance behavior have to be ensured. The obtained long-term results which will be presented are based on diverse 193 nm excimer laser tube improvements aiming at e.g. optimizing the gas flow dynamics and have extended the operational life the laser tube for the first time over several billion pulses even under high duty-cycle conditions.
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Conference 9736:
Laser-based Micro- and Nanoprocessing X
9736-61, Session PTue
Gustavo F . B . Almeida, Renato J . Martins, Adriano J . G .
Otuka, Jonathas P . Siqueira, Cleber R . Mendonça, Univ . de
São Paulo (Brazil)
9736-63, Session PTue
Lei Liu, Xi Huang, Univ . of Nebraska-Lincoln (United
States); Shuo Li, Univ . of Pittsburgh (United States); Yao
Lu, Univ . of Nebraska-Lincoln (United States); Kevin P .
Chen, Univ . of Pittsburgh (United States); Yongfeng Lu,
Univ . of Nebraska-Lincoln (United States)
Laser Induced Periodic Surface Structure (LIPSS) has been observed since the laser invention. The most accepted theory to explain this phenomenon is the interference between the incident light with surface plasmon polaritons waves. Femtosecond laser micromachining is a very active research on
LIPSS, that recently has been incorporated with pulse shaping methods.
In this study, 35 fs laser pulses from a multi-pass amplifier (780 nm and 1 kHz repetition rate), with pulse energy of 18 ?J, were temporally shaped by a Spatial Light Modulator to produce LIPSS on silicon surface. The
Fourier transformed limited (FTL) pulse was shaped into pulse trains with different subpulse separation of 64 fs, 85 fs, 128 fs and 170 fs. The focused beam was scanned by a galvanometric mirror, exposing the sample to 2 laser shots per area for each pulse train. Atomic Force Microscopy images revealed the presence of periodic structures. The 2-dimensional Fast Fourier
Transforms (2D-FFT) of the LIPSS follows the behavior expected for the efficiency factor predicted by theory. The distinct subpulse separation resulted in different carrier densities at the end of the pulse train due to carrier relaxation between each subpulse, which leads to distinct efficiency factors. In conclusion, we investigated LIPSS formation on silicon upon irradiation with fs- pulse trains, which can give additional control of the micromachining process by altering the laser energy deposition in the material.
An effective method for enhancing optical emission signal in laser-induced breakdown spectroscopy (LIBS) has been studied. A Nd:YAG laser with a wavelength of 532 nm was used for sample ablation and plasma generation.
A butane micro-torch was used to generate a small flame. The flame was placed above and parallel to the sample surface. The laser-induced plasmas were generated inside the flame. Enhancement of optical emission and signal-to-noise ratio (SNR) has been observed with the plasmas generated in the flame. For the laser with an energy of 20 mJ/pulse, the observation of optical emission intensity with delay time showed that signals were greatly enhanced in the initial several microseconds. The study of SNR time evolution showed that the maximum SNR occurred at a delay time of around 2 µ s. The laser energy effects on the enhancement of optical emission intensity and SRN were also studied, which indicated laser energy dependent for the enhancement factor. The limit of detection (LOD) for aluminum in steel was estimated, which showed that the detection sensitivity was improved and the LOD of Al decreased from 18 to 6 ppm without and with micro-torch, respectively. The method of generating plasmas in a micro-troch flame was demonstrated to be an effective method for detection sensitivity improvement, especially in the situation of low laser ablation energy.
9736-62, Session PTue
Myeong Hwan Oh, Chung Yun Kang, Pusan National Univ .
(Korea, Republic of)
9736-64, Session PTue
Bogusz D . Stepak, Arkadiusz J . Antonczak, Konrad
Szustakiewicz, Celina Pezowicz, Krzysztof M . Abramski,
Wroclaw Univ . of Technology (Poland)
The Laser Welded Blank(LWB) and hot-stamping hybrid process is the new technologies being developed to improve crash performance of hot stamping parts and maximize the effect of weight reduction. But, during the
LWB of Al-10wt%Si coated boron steel, Al and Si, which are the elements of coated layer, are diluted and segregated randomly in the fusion zone. In the hot stamping process, fusion zone transforms into martensite+ferrite, and fracture occurred at the fusion zone.
In this study, we investigated solutions for LWB using the filler wire contains
C, Mn and hot-stamping hybrid Process of Al-Si coated boron steel for automotive. After hot stamping, the LWB joints that without the filler wire, fracture occurred at the fusion zone. The phase transformation in the fusion zone was depending on the composition of the Al content and the phase transformation behavior changes during the heating, the A3 temperature of Al segregated zone is greater than 950°C the martensite+bainite phase transforms into austenite+ferrite and ferrite is precipitated during the process of moving to a die. Lastly, during the die quenching, austenite transformed martensite only. In contrast, using the high carbon filler wire, fracture occurred at the base metal. Because diluted the high carbon filler wire in the fusion zone, makes Al-segregated zone transform full austenite and then transformed to martensite.
In the range of long pulse laser sources, an ArF excimer laser appears as a good tool for laser micromachining of bioresorbable polymers such as poly(L-lactide). The laser micromachining technique enables manufacturing a complex, submillimeter geometrical shapes such as vascular stents what is not possible to produce using traditional techniques f.e. injection moulding or mechanical treatment. In general, the use of proper laser source allows for limitation of a heat load which is very important factor considering thermal sensitivity of polylactide and its derivatives which are used in biomedical applications. Furthermore, ArF excimer laser can be also used for surface functionalization in terms of geometrical and chemical sense.
Due to long pulse duration of nanosecond laser, however, there is a risk of heat diffusion and accumulation which may cause thermal degradation.
In addition, due to short wavelength (193 nm) photochemical process can modify the chemical composition of ablated surfaces. The motivation for this research was to evaluate the influence of laser treatment on physicochemical properties of polylactide after erosive laser processing. We analysed degradation extent of laser machined samples by using differential scanning calorimetry (DSC). It allowed us to find the optimal process parameters for preserving low degradation and possibly high throughput.
The chemical composition of the ablated surface was investigated by FTIR in attenuated total reflectance (ATR) mode.
146 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9736:
Laser-based Micro- and Nanoprocessing X
9736-20, Session 5
(Invited Paper)
Johannes Heberle, Peter Bechtold, Johannes Strauß,
Michael Schmidt, Friedrich-Alexander-Univ . Erlangen-
Nürnberg (Germany)
Electro-optical (EOD) and acousto-optical (AOD) scanner systems are based on deflection of laser light within a solid state medium. As they do not contain any moving parts, they yield advantages compared to mechanical scanners which are conventionally used for laser beam deflection. Even for arbitrary scan paths high feed rates can be achieved.
The principles of operation and characteristic properties of EOD and AOD are presented. Additionally, a comparison to mirror based mechanical deflectors regarding deflection angles, speed and accuracy is made in terms of resolvable spots and rate of resolvable spots. Especially, the latter one is up to one order of magnitude higher for EOD and AOD compared to others. Further characteristic properties such as response time, damage threshold, efficiency and beam distortions are discussed. Solid state laser beam deflectors are usually characterized by small deflection angles but high angular deflection velocities. As mechanical deflectors exhibit opposite advantages an arrangement of a mechanical scanner combined with a solid state deflector provides a solution with benefits of both systems. As ultrashort pulsed lasers with average power above 100 W and repetition rates in the MHz range are available for several years this approach can be applied to fully exploit their capabilities. Thereby, pulse overlap can be reduced and by this means heat affected zones are prevented to provide proper processing results.
Ultrafast lasers are currently used for both surface and volume processing.
As an example irradiation of focused laser pulses to transparent materials leads to structural changes and opens new avenues for the fabrication of e.g. LED light guiding components. In these applications the laser spot must be as small as 10 µ m with a high lateral resolution in the µ m range.
In order to achieve the industrially required throughput of nearly one
Million laser markings per second, ultrafast lasers with 100 W of average power and PRF of several MHz are required. Laser machining of plastics additionally necessitates a wide spatial separation of the markings to avoid heat accumulation effects. Therefore, neither commercially available galvanometer based nor Polygon based scanners with their limited scan speed can be used for beam deflection. In our work, we developed an experimental setup based on resonant scanners of up to 32 kHz for marking the desired structures and similar applications with writing speeds of more than 1000 m/s on the surface of the sample.
In this paper the details of the new setup will be described. Resonant scanners show a nonlinear movement of the laser spot on the surface of the sample. In order to write equidistant structures the linearization of the nonlinear motion is necessary. In our work, an in-house developed ultrafast laser system with highly dynamic PRF was utilized for the linearization and equidistant spot marking. The laser machining experiments will be presented including new process strategies to avoid thermal side effects.
Further results show the machining quality, accuracy and outstanding throughput of the setup.
9736-23, Session 5
Jan S . Hoppius, Alexander Kanitz, Andreas Ostendorf,
Ruhr-Univ . Bochum (Germany)
9736-21, Session 5
(Invited Paper)
Omer Dolev, Yuval Berg, Niv Gorodesky, Zvi Kotler,
Orbotech Ltd . (Israel)
We report a unique phenomenon where entrance holes are gradually blocked by re-solidification of molten glass droplets, which are ejected during micro-holes percussion drilling of a 200 µ m glass substrate by
UV (355nm) femto- and picosecond laser pulses. When the laser pulse repetition rates are high enough to cause a temperature build-up at the bottom of the hole, molten glass droplets are generated. These melt droplets are ejected during the laser-driven phase-explosion. Due to the rapid cooling of the droplets, the re-solidified glass which clogs the entrance hole holds different physical properties, and its ablation threshold fluence increases in comparison to that of bulk glass. Since the obstruction is not ablated, its dimensions continue to grow as the drilling process continues, sealing the hole’s entrance before a through hole is generated. We have demonstrated control of the self-clogging process by proper thermal management of the drilling process, successfully fabricating either through glass holes or sealed micro-cavities.
Ultrashort laser pulse ablation is one of the most important tools for micro machining. The latest commercialization of laser systems with pulse durations in the pico- and femto-second regime enables nearly non-thermal material processing where heat effects like molten baths and thermal tensions are negligible. Nevertheless, a residual amount of laser energy transforms into heat wherefore cumulative multiple shot processing leads to mentioned thermal affection and therefore lower manufacturing accuracy.
To increase the processing throughput without losing quality it is important to optimize the laser pulse properties and the ablation strategy to avoid the critical thermal ablation. For micro- and nano-processing not only the immediate laser-material interaction but also the substrate dimensions are relevant to consider for accurate ablation. In contrast to bulk material ablation, the heat dissipation is confined by the small heat capacity of microstructures. Especially for complex structures it is time consuming to find efficient processing parameters manually. For this reason, an insitu evaluation system based on electrical resistivity measurements was developed to optimize the laser parameters with instantaneous feedback.
In the work presented, the efficiency of 35 fs pulsed laser ablation was evaluated on copper structures with different dimensions in the micrometer range. Further, these results have been compared and evaluated with surface profiles measured by white-light interferometry.
9736-22, Session 5
Florian Harth, Melissa C . Piontek, Thomas Herrmann,
Johannes A . L’huillier, Photonik-Zentrum Kaiserslautern e .V .
(Germany)
9736-24, Session 5
Marco Smarra, Klaus Dickmann, Fachhochschule Münster
(Germany)
Using ultra-short laser pulses for the generation of microstructures results in a high flexible tool for free form geometries in the micro range.
Increasing laser power and repetition rates increase as well the demand
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Conference 9736:
Laser-based Micro- and Nanoprocessing X of high flexible and efficient process strategies. To increase the ablation efficiency the optimal fluency can be determined, which is a material specific value. By varying the beam shape, the ablation efficiency can be enhanced. In this study a deformable mirror was used to vary the beam shape. This mirror is built by combining a piezo-electric ceramic and a mirror substrate. The ceramic is divided into several segments, which can be controlled independently. This results in a high flexible deformable mirror which influences the beam shape and can be used to vary the spot size or generate line geometries. The ablation efficiency and roughness of small generated cavities were analyzed in this study as well as the dimensions of the cavity. This can be used to optimize process strategies to combine high volume ablation and fine detail generation.
9736-27, Session 6
Marco Smarra, Anja Strube, Klaus Dickmann,
Fachhochschule Münster (Germany)
9736-25, Session 6
(Invited Paper)
Yannick G . Petit, Institut de Chimie de la Matière
Condensée de Bordeaux (France); Konstantin Mishchik,
Eungjang Lee, Ctr . Lasers Intenses et Applications
(France); Etienne Brasselet, Univ . Bordeaux 1 (France);
Arnaud Royon, Ctr . Lasers Intenses et Applications
(France); Inka B . Manek-Hönninger, Univ . Bordeaux 1
(France); Sylvain Danto, Thierry Cardinal, Institut de
Chimie de la Matière Condensée de Bordeaux (France);
Lionel Canioni, Univ . Bordeaux 1 (France)
Using ultra-short laser pulses for micro structuring or drilling applications reduces the thermal influence to the surrounding material. The best achievable beam profile equals a Gaussian beam. Drilling with this beam profiles results in cylindrical holes. To vary the shape of the hole, the beam can either be scanned or – for single pulse and percussion drilling – manipulated by masks or lenses. A high flexible method for beam shaping can be realized by using a deformable mirror. This mirror contains a piezo-electric ceramic, which can be deformed by an electric potential. By separating the ceramic into independent controllable segments, the form of the surface can be varied individually. Due to the closed surface of the mirror, there is no loss of intensity due to diffraction. The mirror deformation is controlled by Zernike polynomials and results e.g. in a lens behavior. In this study a deformable mirror was used to generate e.g. slots in thin steel foils by single pulse and percussion drilling using ultra-short laser pulses.
The influence of the cylindrical deformation to the laser beam and the resulting geometry of the generated holes was studied. It was demonstrated that due to the high update rate up to 150 Hz the mirror surface can be varied in each scan cycle, which results in a high flexible drilling process.
On the one hand, singular optics is a very active modern field of research, which corresponds to the manipulation of structured light, referring to electromagnetic fields endowed with phase or polarization singularities
(also called optical vortices). On the other hand, femtosecond direct laser writing (DLW) has largely shown to be a very powerful approach for material structuring, improving the fundamental knowledge of laser/matter interaction as well as the ability to manufacture advanced materials with tailored optical functionalities. The combination of these two fields, namely vortex-induced DLW, opens promising perspectives in terms of material structuring, giving access to original structures that cannot be obtained with standard Gaussian beams.
While vortex-induced DLW was initially used for the structuring of surface topology, we recently demonstrated for the first time its high potential for bulk structuring [1], leading to sub-wavelength features with linear and nonlinear optical properties in innovative silver-containing glasses [2], as index change, silver cluster fluorescence, electric field induced second harmonic generation due to an unique ability of single-beam direct laser poling [3], and even plasmonic properties of metallic nanoparticles [4].
Finally, vortex-induced DLW should further lead to breakthroughs in alloptical superresolution structuring in oxide materials, to compete nanoscale manufacturing technologies, especially thanks to STED-like approaches.
[1] K. Mishchik et al., Opt. Lett., 40(2), 201-204 (2015).
[2] A. Royon et al., Opt. Mat. Expr. 1(5), 866-882 (2011) [invited].
[3] G. Papon et al., Appl. Phys. Lett. 96, 113103 (2014).
[4] N. Marquestaut et al., Adv. Funct. Mat. 24(37), 5824-5832 (2014).
9736-26, Session 6
(Invited Paper)
Joerg Schille, Lutz Schneider, Andrè Streek, Lars Hartwig,
Sascha Kloetzer, Udo Loeschner, Hochschule Mittweida
(Germany)
No Abstract Available
9736-28, Session 7
(Invited
Paper)
Robert Kammel, Friedrich-Schiller-Univ . Jena (Germany);
Klaus Bergner, Friedrich Schiller Univ . Jena (Germany);
Jens Thomas, Roland Ackermann, Friedrich-Schiller-Univ .
Jena (Germany); Stefan Skupin, Ctr . Lasers Intenses et
Applications (France); Stefan Nolte, Friedrich-Schiller-Univ .
Jena (Germany) and Fraunhofer-Institut für Angewandte
Optik und Feinmechanik (Germany)
Ultrashort pulse lasers enable reliable and versatile high precision ablation and surface processing of various materials such as metals, polymers and semiconductors. However, when modifications deep inside the bulk of transparent media are required, detrimental nonlinear pulse material interactions can decrease the precision, since weak focusing and the long propagation of the intense pulses within the nonlinear media may induce
Kerr self focusing, filamentation and white light generation. In order to improve the precision of those modifications, simultaneous spatial and temporal focusing (SSTF) allows to reduce detrimental nonlinear interactions, because the ultrashort pulse duration is only obtained at the focus, while outside of the focal region the continuous increase of the pulse duration strongly reduces the pulse intensity.
Imaging the optical breakdown by means of pump-probe shadowgraphy we investigate the temporal evolution of the femtosecond (fs) laser induced plasma and disruption formation in transparent media for SSTF and conventional focusing using focusing conditions typically used for intraocular fs-laser surgery (NA = 0.1). With conventional focusing the complex interplay of self focusing and filamentation induces strongly inhomogeneous disruptions with a length > 1 mm, while self-phase modulation results in intense white light generation. In contrast, disruptions induced by SSTF are homogeneously located at the focal plane and reduced in length by a factor >2 compared to conventional focusing. Moreover, no significant broadening of the pulse spectra is observed, which is in excellent agreement with numerical simulations of the nonlinear pulse propagation and might favor SSTF for demanding applications such as intraocular fslaser surgery.
148 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9736:
Laser-based Micro- and Nanoprocessing X
9736-29, Session 7
(Invited Paper)
Peter G . Kazansky, Martynas Beresna, Jingyu Zhang,
Rokas Drevinskas, Aabid Patel, Au?ra Cerkauskaite,
Optoelectronics Research Ctr . (United Kingdom) approach for the surface pre-treatment of an adhesively bonded composite joint are given.
9736-31, Session 7
Girolamo Mincuzzi, Marc Faucon, Rainer Kling, ALPhANOV
(France)
Femtosecond laser writing in transparent materials has attracted considerable interest due to new science and a wide range of applications from laser surgery, 3D integrated optics and optofluidics to geometrical phase optics and ultra-stable optical data storage. A decade ago it has been discovered that under certain irradiation conditions self-organized subwavelength structures with record small features of 20 nm, could be created in the volume of silica glass. On the macroscopic scale the selfassembled nanostructure behaves as a uniaxial optical crystal with negative birefringence. The optical anisotropy, which results from the alignment of nano-platelets, referred to as form birefringence, is of the same order of magnitude as positive birefringence in crystalline quartz. The two independent parameters describing birefringence, the slow axis orientation
(4th dimension) and the strength of retardance (5th dimension), are explored for the optical encoding of information in addition to three spatial coordinates. The slow axis orientation and the retardance are independently manipulated by the polarization and intensity of the femtosecond laser beam. The data optically encoded into five dimensions is successfully retrieved by quantitative birefringence measurements. The storage allows unprecedented parameters including hundreds of terabytes per disc data capacity and thermal stability up to 1000°. Even at elevated temperatures of
160oC, the extrapolated decay time of nanogratings is comparable with the age of the Universe - 13.8 billion years. The demonstrated recording of the digital documents, which will survive the human race, including the eternal copies of Kings James Bible and Magna Carta, is a vital step towards an eternal archive.
Surface Blackening by Ultra-Short Pulses Laser (UPL) texturing for industrial applications (aerospace, electronics, decoration etc.) passes through the use of both fast beam scanning systems and high repetition rate, High Power P,
UPL. Nevertheless unwanted thermal effects are expected when P exceed some tens of W. An interesting strategy for a reliable heat management would consists in texturing with a low fluence values (slightly higher than the ablation threshold) and utilising a Polygon Scanner Heads delivering laser pulses with unrepeated speed.
Here we show for the first time that over stainless steel, it is possible to obtain surface blackening by utilising a 2 MHz femtosecond laser jointly with a fast and accurate polygonal scanner head at relatively low fluence
(0.11 J·cm-2). Different surface textures have been obtained varying the scan speed between 25 m·s-1 to 90 m·s-1. In particular, spikes formation process has been shown and optimised at 25 m·s-1 and a full morphology characterization by SEM has been carried out. Reflectance measurements carried out in visible and IR range (up to 2 µ m) with integrating sphere will be presented to compare reference textures with high scan rate textures. In the best case a surface reflectance value < 5% has been extracted.
9736-30, Session 7
Stefan Kreling, Hinrich Grefe, Klaus Dilger, Technische Univ .
Braunschweig (Germany)
Pulsed lasers with spot diameters in the µ m range are widely used for the aerial treatment of surfaces. Typical applications are cleaning of composite molds, paint stripping, laser heating or surface pre-treatment prior to adhesive bonding.
In these cases the aerial treatment by small laser spots is achieved by overlapping the spots to lines in x-direction and the single lines to an area in y-direction. During this application the treatment result is significantly influenced by the distance between the single lines, called the hatch distance as well as the single spot overlap, which is defined by the ratio of spot diameter and pulse repetition rate to the line feed.
Taking a closer look at this treatment strategy it becomes obvious that due to the overlapping of circular pulses an uneven distribution of the number of laser pulses which hit each aerial increment appears.
The background of the approach taken here was the comparison of different pre-treatment parameters for adhesive bonding by calculating an accumulated energy, being the pulse energy multiplied by the average amount of pulses hitting each surface increment. The latter one was found using a numerical approach, depicting the distribution of laser pulses on the surface depending on the parameters spot size, pulse repetition rate, line feed and hatch distance. Based on the numerical model an empirical formula was derived which enables an easy calculation of the average number of laser pulses which hit each aerial increment of the surface.
As an outlook some experimental results which were gathered using this
9736-32, Session 8
(Invited Paper)
Yoshiki Nakata, Noriaki Miyanaga, Osaka Univ . (Japan)
In interfering femtosecond laser processing, energy is induced periodically according to an interference pattern. When a metallic thin film is processed, each spot in the interference pattern is partially melted, and then freezes due to a drop in temperature. The interference patterns change according to the phase shift and power ratio between the interfering beams, and are transcribed to the processed pattern. Furthermore, the temperature distribution of the film, which changes in time and space, governs the viscosity and surface tension. The resultant structures are very simple and unique, and include nanowhiskers, nanobumps, nanodrops, and metallic hole arrays. These can have applications in fields such as nanotechnology and metamaterial technology, for example, as plasmonic devices, such as surface-enhanced Raman spectroscopy templates. Our recent results will be presented.
9736-33, Session 8
Yin-Kuang Yang, National Tsing Hua Univ . (Taiwan); Yu-
Xiang Wu, Te-Hsun Lin, Chun-Wen Yu, National Tsing Hua
University (Taiwan); Chien-Chung Fu, National Tsing Hua
Univ . (Taiwan)
Laser interference lithography (LIL) is a maskless lithography technique with many advantages such as simple optical design, low cost, infinite depth of
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Conference 9736:
Laser-based Micro- and Nanoprocessing X focus, and large area patterning with single exposure. However, the intensity of normal laser beam is Gaussian distribution. In order to obtain large area uniform structure, we have to expand the laser beam much larger than the wafer and use only the central part of the beam, resulting in wasting lots of energy and low production capacity. In this study, we designed a beam shaping device which consists of two parallel fused silicon optical windows with different coating on the opposite side. When the expanded laser beam pass through the device, the beam will experience several times of partial reflections between two optical windows, and the transmittance of laser beam will depends on the incident angle. The output intensity distribution will change from Gaussian distribution to a flat top distribution. In our experiment, we combined the beam shaping device with a Lloyd’s mirror LIL system. The results indicated that the LIL system with beam shaping device can obtain large area uniform pattern. And compare with the normal Lloyd’s mirror LIL system, the exposure time is shorten up to 5 times. In conclusion, this study design a beam shaping device for LIL system. The flat top beam produced by the device can improve the large area uniformity and the production capacity of traditional LIL system. Making LIL more suitable for industry application.
great importance for large area printed electronics. The materials commonly used is metals, carbon powder or conductive polymers in the form of inks. A more recent development is the use of graphene or Graphene Oxide (GO).
GO is a poor conductor but after reduction the conductivity can increase several orders of magnitude. GO has a much lower cost than metal inks and if coated over large areas of the substrate, the parts that needs to be conductive can be selectively reduced. This makes laser assisted reduction of GO a promising and fast process method for fabrication of conductive tracks on large area paper based substrates. The GO was prepared on several different paper substrates and conductive tracks where fabricated by using and evaluating different laser sources coupled to a laser scanning mirror system. We will present our investigation showing promising results, but is highly dependent on several laser parameters as well as GO layer thickness and density. A reduction of sheet resistance from 3.5 MOhm for unreduced r-GO down to ~550 Ohm is obtained without any observable damage to the paper substrates.
9736-34, Session 8
Valentin Lang, Teja Roch, Andres F . Lasagni, TU Dresden
(Germany) and Fraunhofer IWS Dresden (Germany)
Periodic surfaces structures with micrometer or submicrometer resolution produced on the surface of components can be used to improve their mechanical, biological or optical properties. In particular, these surfaces can control the tribological performance of parts, for instance in the automotive industry. In the last years, important efforts have been made to develop new technologies capable to produce functionalized surfaces. One of these technologies is the Direct Laser Interference Patterning (DLIP) technology, which permits to combine high fabrication speed with high resolution even in the sub-micrometer range. In DLIP, a laser beam is split into two or more coherent beams which are guided to interfere on the work piece surface.
This causes modulated laser intensities over the component’s surface, enabling the direct fabrication of a periodic pattern based on selective laser ablation or melting. Depending on the angle between the laser beams and the wavelength of the laser, the pattern’s spatial period can be perfectly controlled. In this study, we introduce new modular DLIP optical heads, developed at the Fraunhofer IWS and the Technische Universität Dresden for high-speed surface laser patterning of polymers and metals. For the first time it is shown that effective patterning speeds of up to 0.7 m2/min and 0.4 m?/min are possible on polymer and metals, respectively. Line and dot-like surface architectures are shown with spatial periods between 5 µ m and 22 µ m are shown. The coefficient of friction of patterned steel under lubricated conditions is reduced by 25%.
9736-36, Session 8
Denise Guenther, TU Dresden (Germany); Jaoine Valle,
Saioa Burgui, Carmen Gil, Cristina Solano, Alejandro
Toledo-Arana, Univ . Pública de Navarra (Spain); Ralf
Helbig, Leibniz-Institut für Polymerforschung Dresdene e .V .
(Germany); Carsten Werner, Leibniz Institute of Polymer
Research Dresden (Germany); Inigo Lasa, Univ . Pública de
Navarra (Spain); Andrés F . Lasagni, TU Dresden (Germany)
In the past 15 years, many efforts were made to create functionalized articial surfaces showing special anti-bacterial and anti-biofouling properties.
Thereby, the topography of medical relevant materials plays an important role. However, the targeted fabrication of promising surface structures like hole-, lamella- and pyramid-like patterns is still a challenge. Optical and e-beam lithography, mouling and self-assembly layers show a great potential to design topographies for this purpose. At the same time, most of these techniques are based on sequential processes, require masks or moulds and thus are very device relevant and time consuming. In this work, the Direct Laser Interference Patterning Technology (DLIP) as a sophisticated technology for the fast, flexible and direct creation of periodic micrometer- and submicrometer structures is presented. This method offers the possibility to equip large plain areas and curved devices with 1D,
2D and 3D patterns. Simple 1D (e.g. lines) and complex 3D (e.g. lamella, hierarchichal pillars) patterns with feature sizes from 300 nm to 5 µ m were fabricated on polymeric materials (PS and PET). Subsequently, adhesion behavior of S. aureus and S. epidermidis bacteria was characterized under in-vitro and in-vivo conditions. The results revealed that the topographies in micrometer scale have a significant impact on bacterial adhesion. On the one hand, one-dimensional line-like structures especially with dimensions of the bacteria enhanced microbe attachement. While on the other hand, complex three-dimensional patterns prevented biofilm formation even after implantation and contamination in living organisms.
9736-35, Session 8
Enkeleda Balliu, Henrik Andersson, Magnus Engholm, Sven
Forsberg, Håkan Olin, Mid Sweden Univ . (Sweden)
9736-37, Session 8
Patrick S . Salter, Yu-Chen Chen, Bangshan Sun, Jason M .
Smith, Martin J . Booth, Univ . of Oxford (United Kingdom)
Printed electronics is becoming more popular for fabrication of applications on flexible substrates. The substrates have mainly been plastics but the use of paper is becoming more widespread due to lower cost and recyclability.
Consider also the possibility of using the very large area manufacturing techniques, today used in the paper making industry, for production of electronic applications. Manufacturing of conductive tracks at low cost is of
We demonstrate the versatility of direct laser writing for restructuring diamond. An ultrashort pulsed beam is focused into diamond at high numerical aperture. The structural modifications resulting from multiphoton absorption at the focus are highly localised in three dimensions. The incident laser beam is shaped using adaptive optics to remove the severe aberrations
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Conference 9736:
Laser-based Micro- and Nanoprocessing X induced at the diamond interface, such that accurate fabrication can be achieved over a large 3D volume. At higher pulse energies, the breakdown of the diamond lattice occurs at the laser focus to leave an amorphous carbon phase. The laser focus may be subsequently traced through the diamond to create continuous conductive wires. Adaptive optics aberration correction is essential for low resistivity wires which can follow three dimensional paths.
These wires are showing great promise in diamond based sensors. We also introduce a new fabrication regime in diamond whereby reducing the pulse energy we are able to demonstrate the generation of nitrogen vacancy
(NV) colour centres. With careful control over the incident pulse energy it is possible to gently perturb the diamond lattice with a single pulse to cause minimal structural disruption. Such modifications are not visible by conventional transmission microscopy, but can be seen in a confocal microscope mapping photoluminescence. Following a high temperature anneal, the laser modified sites exhibit spectroscopic properties strongly characteristic of NV- colour centres. Hanbury-Brown Twiss measurements provide a strong indication that the laser processing has resulted in single isolated NV- defects: atomic level restructuring with minimal surrounding damage. wavelengths between 350 and 1200 nm show a high transmission for the matrix resin, or in case of high absorption (10,6 µ m) a thermal degradation of the polymer. Both effects lower the quality of the pre-treatment process.
Contrary laser radiation with 3 µ m wavelength has a high absorption in the matrix resin with a correlating optical penetration depth which is smaller than the thickness of the resin layer. In addition the thermal degradation is lower compared to CO2 laser radiation. This provides the opportunity for a sensitive laser-based surface pre-treatment.
During this investigation the interactions of the 3 µ m laser radiation with reinforced and non-reinforced epoxy are evaluated and compared with a classic fiber laser and an UV-laser. As well mechanical (e.g. ablation behavior) as chemical (matrix degradation) are considered. It could be shown, that the contaminations can be removed damage free with the new wavelength.
9736-38, Session 9
(Invited Paper)
Masayuki Okoshi, National Defense Academy (Japan) and
Kanto Gakuin Univ . (Japan)
9736-40, Session 9
Richard M . Carter, Heriot-Watt Univ . (United Kingdom);
Michael Troughton, Selex ES Ltd . (United Kingdom);
Jianyong Chen, Heriot-Watt Univ . (United Kingdom); Ian F .
Elder, Selex ES Ltd . (United Kingdom); Robert R . Thomson,
Heriot-Watt Univ . (United Kingdom); Robert A . Lamb,
Selex ES Ltd . (United Kingdom); M . J . Daniel Esser, Duncan
P . Hand, Heriot-Watt Univ . (United Kingdom)
Nanoswellings of 60 nm height and 500 nm diameter on average of an iron thin film deposited on a silica glass substrate at regular intervals of
2.5 micron were fabricated by the irradiation of a 157 nm fluorine laser. The fluorine laser was focused on the iron thin film by each microsphere made of silica glass of 2.5 micron diameter, which covered the entire surface of the films. The surface of the silica glass substrate underneath the fluorine laser irradiated iron thin film selectively swelled to push up the film. After the laser induced micro/nanostructuring, the fluorine laser was again irradiated onto the entire surface of the periodic micro/nanostructured iron thin film to form an approximately 2 nm thick Fe3O4 modified layer. As a result, the samples showed hydrophobicity and high corrosion resistance to 3 wt% NaCl aqueous solution (quasi-seawater). No rust was observed on the samples after the immersion test in the quasi-seawater for 24 h.
We report on practical, industrially relevant, welding of optical components to aluminum alloy components. Weld formation is achieved through the tight focusing of a 5.9ps, 400kHz Trumpf laser operating at 1030nm. By selecting suitable surface preparation, clamping and laser parameters, the plasma can be confined, even with comparatively rough surfaces, by exploiting the melt properties of the glass. The short interaction time allows for a permanent weld to form between the two materials with heating limited to a region ~300 µ m across. Practical application of these weld structures is typically limited due to the induced stress within the glass and, critically, the issues surrounding post-weld thermal expansion. We will comment on these issues, presenting measurements of the induced stress within the glass component and present a range of weld geometries and pre-welding surface preparations to minimise post-welding thermal issues.
In addition we will report on both the mechanism of the weld formation and on the measured strength of the weld, with a particular emphasis on laser parameters and surface preparation. A measured weld strength at least one order of magnitude greater than equivalent adhesive bonding approaches will be presented.
9736-39, Session 9
µ
David Blass, Stefan Kreling, Technische Univ . Braunschweig
(Germany); Sebastian Nyga, Thomas Westphalen, Bernd
Jungbluth, Hans-Dieter Hoffman, Fraunhofer institute for laser technology (Germany); Klaus Dilger, Technische Univ .
Braunschweig (Germany)
9736-41, Session 9
Yury Kuzminykh, Seyed Payam Vahdati, EMPA
(Switzerland); Annika Richmann, Bernold Richerzhagen,
Synova S .A . (Switzerland); Patrik W . Hoffmann, EMPA
(Switzerland)
The application of carbon fiber reinforced plastics in combination with adhesive bonding has a high potential for the mass reduction of structural automotive parts. Due to the mold based manufacturing process of the composite parts, surface contaminations (e.g. release agents residues) are inevitable. Therefore a surface pre-treatment prior to the bonding process is necessary. State of the art pre-treatment processes are mechanical treatments like manual abrading or grit blasting which increase the production time.
As an alternative approach laser radiation offers the possibility for a sufficient (clean surfaces) and efficient (high process speeds) surface pre-treatment. Unfortunately the most common laser sources with their
Laser micro-machining of sapphire is a demanded technology, which is not yet perfectly mastered. In our contribution we investigate the ablation process of sapphire by a water jet guided frequency doubled Nd:YAG laser
(532 nm) with the pulse length of ~100ns. The laser radiation is guided to the sample surface in a medium pressure (400 bar) laminar water jet of
30-50 µ m diameter by total internal reflection. This set-up allows efficient and high-quality scribing and cutting of sapphire plates of up to several mm thickness. We have investigated the details of the ablation process using a precisely triggered high speed camera with down to 100ns exposure
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time. We have imaged and recorded the dynamics of the ablation plume expansion. Lifetime of the ablation plume is found to be in the range of
400-500ns. The ablation threshold of the sapphire was found to be higher than for the ablation using comparable laser in air. The strong interaction of plasma plume with the water jet has been observed.
9736-42, Session 10
Conference 9736:
Laser-based Micro- and Nanoprocessing X
Muttaqin Yasin, Takahiro Nakamura, Shunichi Sato, Tohoku
Univ . (Japan)
9736-44, Session 10
Christian Schindler, Ernst-Abbe-Hochschule Jena
(Germany); Maria Friedrich, Günter-Köhler-Institut für
Fügetechnik und Werkstoffprüfung GmbH (Germany);
Jens Bliedtner, Ernst-Abbe-Hochschule Jena (Germany)
Graphene oxide (GO) has attracted much attention as a precursor of graphene. But, reduction process of GO is essential to obtain fascinating properties of graphene. Among many reduction methods, reduction of GO by laser irradiation is versatile method to reduce oxygen-based functional groups from GO and is applicable either in colloidal solution or in film form.
In the present study, femtosecond laser pulses (?: 800 nm, pulse width:
100 fs, repetition rate: 300 Hz) were employed, and different parameters such as laser fluence and irradiation time were examined to obtain highly reduced graphene oxide (rGO). By applying different laser fluence with the constant irradiation time, GO solution had optically changed from yellowpale into black. The peak absorption in UV-vis. absorption spectrum shifted from 230 to 275 nm after 2 hours irradiation with the laser fluence of 80 mJ/cm2. Further increase in the irradiation time gave drawbacks result due to re-oxidation of rGO. It was also shown by FT-IR and X-ray photoelectron spectroscopy that oxygen functional groups were effectively reduced after laser irradiation. Additionally, intensity ratio of D and G bands in Raman spectrum of rGO decreased more than 15 % compared to that of GO which is quite different with the conventional chemical or thermal methods.
This indicates that the enhancement of sp2 domains with maintaining the defect sites on GO through the reduction process. Moreover, the electronic conductivity of rGO significantly increased. This demonstrates a potential application of femtosecond laser in synthesize graphene based materials for specific purposes. (249 words)
9736-43, Session 10
Tingyi Gu, Princeton Univ . (United States); Burhan Abdi,
Cornell Univ . (United States); Romain Fardel, Craig B .
Arnold, Princeton Univ . (United States)
Uniform dispersion of metallic and semiconductor nanoparticles in chalcogenide glass matrix is an effective way of modifying glass properties.
Such materials could lead to important applications in active and passive photonic devices. It has previously been shown that sliver particles can be created uniformly in chalcogenide glass. In this work, laser ablation is applied to generate semiconductor particles in arsenic sulphide glass, including germanium or gallium. The chalcogenide glass with the laser assisted liquid phase synthesis is further examined by Raman and photoluminescence spectrum. We identify nanoparticle formation along with formation of semiconductor-sulfide bonds. Spin coated thin films of the nanoparticle doped chalcogenide solution reveal a uniform distribution of nanoparticles.
Non-linear absorption through high intensities and a-thermal ablation allow micro material processing of optical glasses inducing only very low strain. These effects enable new process chains for photonics production fields with ultrashort pulsed laser radiation. We accomplished experiments with an ultrashort pulsed laser system emitting pulses ranging from 350 fs to 10 ps and a maximum average power of 50 W at 1030 nm. The laser beam gets deflected by a galvanometric scan-system with maximum scan speed of 2500 mm/s and focused by F-theta lenses onto the substrates. By design of experiments the influence of pulse energy, fluence and material conditions on the target figures is analysed. These are represented by the material characteristics mean squared roughness, ablation depths as well as the microcrack distribution in depth. The experimental procedure is applied onto a series of quartz glass, SF6 and phosphate glass samples. The findings give suggestions for process windows and display potential for process improvements.
9736-45, Session 11
(Invited Paper)
Michael A . Scarpulla, The Univ . of Utah (United States)
Laser recrystallization of thin film silicon and transparent conducting materials over the entire area is enabling technology for nearly all flat panel displays, including those at the >1 m2 area scale matching solar modules. The challenges in materials and laser sources are severe when trying to extend these techniques to compound semiconductors such as
CdTe and Cu(In,Ga)Se2 (CIGSe). Stoichiometry control is especially critical and challenging for compound semiconductors, which severely restricts the possibilities for liquid phase processing as used for Si. In this talk, the opportunities and restrictions for laser processing in CIGSe and CdTe thin film photovoltaic technologies will be discussed. Process windows for CW and ns pulsed lasers are outlined for processes of crystallization and phase formation as well as for surface modification for contacting and surface passivation. These themes will be illustrated primarily in the context of CdTe but results from CIGSe will also be presented.
9736-46, Session 11
Yijing Zheng, Karlsruhe Institute of Technology (United
States); Johannes Pröll, Karlsruhe Institute of Technology
(Germany); Tim Kunze, Fraunhofer IWS Dresden
(Germany); Andrés-Fabián Lasagni, Fraunhofer IWS
Dresden (Germany) and TU Dresden (Germany); Christian
Brösicke, Karlsruhe Institute of Technology (Germany);
Peter Smyrek, Karlsruhe Institute of Technology (Germany)
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and Karlsruhe Nano Micro Facility (Germany); Hans J .
Seifert, Wilhelm Pfleging, Karlsruhe Institute of Technology
(Germany)
Laser-assisted modification of metals, polymers or ceramics yields a precise adjustment of wettability, biocompatibility or tribological properties for a broad range of applications. Due to a specific change of surface chemistry and/or surface topography on micro- and nano-meter scale, new functional properties can be achieved. A rather new scientific and technical approach is the laser-assisted surface modification and structuring of metallic current collector foils for lithium-ion batteries. Prior to the thick film electrode coating processes, the formation of micro/nano-scaled surface topographies on current collectors is critical with respect to an improvement in film adhesion, mechanical anchoring, and electrical contact. These features in turn impact on the battery performance and the battery life-time.
The volume change during de-/insertion of lithium-ions is crucial for future high power silicon-based anode materials. Volume changes can reach values up to 400% causing delamination of the active material from the current collector leading to dramatic capacity loss after few cycles.
In order to enhance the adhesion of thick film anode materials, the formation of 3D surface architectures on copper current collectors is investigated by applying two advanced laser processing structuring technologies: laser direct interference patterning (DLIP) and ultrafast laserinduced periodic surface structuring.
The formation of laser-induced periodic surface structures (LIPSS) on metallic surfaces was investigated as function of laser parameters such as wavelength, scanning speed, pulse number, and laser fluence. Well defined
LIPSS with periodicities from 200 nm up to 440 nm could be generated.
Hierarchical structures combined with LIPSS were fabricated by using appropriate laser parameters. Also, hydrophobic properties with water contact angles of about 145° could be measured.
With respect to the direct laser interference patterning (DLIP) of current collector foils, a laser beam with ns or ps pulse lengths was split into several collimated and coherent laser beams and finally superimposed on the metallic surface. By adjustment of the processing parameters, line structures with periodicity from 1.3 µ m up to 10 µ m were formed on surfaces.
After laser structuring via LIPSS or DLIP, silicon-based as well as graphitebased composite materials were deposited by tape-casting on the modified current collectors. The electrode film adhesion was characterized by tensile strength measurements and the electrochemical performance was measured within cycling of battery test cells.
9736-47, Session 11
Conference 9736:
Laser-based Micro- and Nanoprocessing X
Peter Smyrek, Johannes Pröll, Karlsruhe Institute of
Technology (Germany) and Karlsruhe Nano Micro
Facility (Germany); Hans J . Seifert, Karlsruhe Institute of Technology (Germany); Wilhelm Pfleging, Karlsruhe
Institute of Technology (Germany) and Karlsruhe Nano
Micro Facility (Germany)
The development of new active materials, electrode architectures and innovative manufacturing strategies for lithium-ion batteries is quite important in order to optimize battery performance and production cost.
In recent years, strong efforts have been undertaken to study physical and chemical properties of cathode materials which develop towards the direction of high energy density, high power density, long cycle life and environment friendly. Lithium nickel manganese cobalt oxide (NMC) has been reported as one of the promising cathode material because of its many advantages such as high rate capability and good thermal stability.
Nevertheless, for automotive applications lithium-ion batteries require extended cycle and calendar life-time. For this purpose, prediction and estimation of battery life-time and degradation mechanisms are of great interest. Previous studies have shown that laser-structuring of threedimensional (3D) micro-pillars in cathode thick films increases the active skin surface and therefore the lithium-ion diffusion kinetics. Within this study, NMC thick films were prepared by tape-casting and subsequent ultrafast laser-structuring. The lithium distribution in electrochemically cycled and unstructured / fs laser-structured NMC cathodes was investigated post-mortem by using Laser-Induced Breakdown Spectroscopy
(LIBS). The main goal is to develop an optimized three dimensional cell design with improved electrochemical properties based on studies of the homogeneity of the local State-of-Charge. LIBS experiments were carried out using a LIBS workstation (type: FiberLIBS SN013, Secopta GmbH,
Germany) equipped with a mode-locked DPPS Nd:YAG laser operating at a wavelength of 1063nm. The element distribution was investigated using two different techniques: element mapping and element depth-profiling of the unstructured / fs laser-structured electrode surface. Results achieved from post-mortem studies using LIBS will be presented.
9736-48, Session 11
Jinguang Cai, Akira Watanabe, Tohoku Univ . (Japan)
Recently, the rapid development of miniaturized portable electronic devices has greatly motivated the study on micro-/nano-scale power supply units with high energy and high power densities. Supercapacitors have been widely studied over the past few years due to their high power density, robust cycle performance, pollution-free operation, and maintenance-free features. Besides, supercapacitors with small size, light weight, flexibility while maintaining high energy and power output are required for portable miniaturized electronics. In-plane micro-supercapacitors (MSCs) are recognized as the potential power supply units in portable devices, due to their simplified packaging processes and compatibility to the integrated circuits. However, the fabrication methods and materials should be costeffective, scalable, and compatible to current electronic industry. Carbon materials own high specific surface areas, electrochemical stability, and high electrical conductivity, which are critical parameters for high-power supercapacitors. Moreover, the high mechanical tolerance makes them good candidates for flexible wearable devices. Therefore, MSCs based on carbon materials would satisfy the requirements of portable electronics.
In this work, we demonstrated the fabrication of flexible carbon MSCs by laser direct writing on commercial polyimide sheets with very cheap CW laser diode. The structures and compositions of obtained carbon materials are detailedly characterized as pore structures, which may be in favor for the immersion of electrolyte. As-prepared micro-supercapacitors show a high capacitance of about 9 mF/cm2 at a scanning rate of 10mV/s, which is comparable to the reported highest capacitance of carbon-based supercapacitors fabricated by pulse-laser writing. In addition, the flexible micro-supercapacitors have high bend tolerance and long-cycle stability.
9736-49, Session 11
Jim M . Bovatsek, Rajesh S . Patel, Robert S . Sposili,
Spectra-Physics (United States); Rukun Yang, Xueke
Wu, Shenzhen Geesun Automation Technology Co ., Ltd .
(China)
Pulsed infrared (IR) lasers have, in many cases, successfully replaced mechanical punching processes for Li-ion battery foil cutting. While the lower cost of IR pulsed lasers is attractive to manufacturers, IR laser process has its limitations. It can leave a large heat affected zone on the tab material and a sharp burr attached to the cut edge. These can potentially be a safety
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Conference 9736:
Laser-based Micro- and Nanoprocessing X hazard for batteries during their life cycle. Past studies have shown that using green or ultraviolet (UV) lasers, smaller kerf width and better edge quality can be achieved. However, the cutting speed achieved was low and not acceptable to battery manufacturers due to the lower power of green and UV lasers. With recent advances in laser technology, we at Spectra-
Physics® have developed cost effective high power, high repetition rate green and UV lasers that can solve the cutting speed problem. In this paper, we present Li-ion battery foil cutting results achieved using our high power nanosecond Quasar® hybrid fiber laser with pulse-shaping technology. The results show speeds of 1 m/s or higher can be achieved with a burr size of 10 um or less for cutting current-carrying conductors, anode, and cathode foils.
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9737-1, Session 1
Christoph Rehbock, Alexander Heinemann, Janina
Zwartscholten, Stephan Barcikowski, Univ . Duisburg-Essen
(Germany)
Gold Submicrometer spheres (Au-SMS) are applicable in optics due to their well-defined uniform shape combined with a very high scattering cross section. As synthesis of these nanostructures via chemical synthesis proofs to be difficult, the process of Pulsed Laser Melting in Liquids (PLML) has been well established to synthesize SMS from a broad range of materials using aggregated source nanoparticles [1,2].
In this work we used the totally biocompatible additive NaCl to induce aggregation of laser-generated gold nanoparticles, while in a consecutive step we performed reirradiation with a ns-laser (?=532 nm). We could confirm the formation of Au-SMS, size controlled in a regime of 200-400 nm by laser fluence. Interestingly, we found that along with increasing average fluence the portion of wrinkled surface textures became more abundant. This is most likely due to the partial onset of fragmentation processes and deposition of small particles on the SMS. Additionally, we could show that the surface texture of the SMS critically depends on the size distribution of the educt material [3]. These strategies could give access to
SMS with tailor-made surface structures e.g. for SERS-applications.
References:
[1] A. Pyatenko, H. Wang, N. Koshizaki, T. Tsuji, Laser & Photonics Reviews,
1-9 (2013)
[2] T. Tsuji, T. Yahata, M. Yasutomo, K. Igawa, M. Tsuji, Y. Ishikawa, N.
Koshizaki, Physical Chemistry Chemical Physics, 3099–3107 (2013).
[3] C. Rehbock, J. Zwartscholten and S. Barcikowski, Chem. Lett., 2014, 43,
1502-1504.
the surfaces are irradiated interferentially by high power laser pulses. The morphologies of the nanostructures are studied by atomic force microscopy.
The period of the grating is varied by varying the laser wavelengths used as well as the interference angle. The nanowires are usually produced by a single application of laser interference but also observed from the surfaces irradiated by a few times.
9737-3, Session 1
(Invited
Paper)
Tatiana E . Itina, Andrey Voloshko, Lab . Hubert Curien
(France)
Nanoparticles have found numerous applications in such areas as photonics, electronics, medicine, etc. Further development of these fields requires reliable and versatile methods of nanoparticle synthesis with well-controlled properties. Among promising synthesis techniques, both laser ablation and plasma discharges are considered. These methods provide numerous advantages that are unique in several cases. On one hand, the main advantage of the laser ablation method is in the possibilities of changing laser parameters and background conditions and in its capacity to preserve stoichiometry. Laser-based methods also yield bio-compatible nanoparticles and nano-colloids with unique chemical properties. Laser-induced fragmentation provides additional control ways over nanoparticle sizes.
In addition, doubled and shaped laser pulses can be applied for a better control over nanoparticle sizes. On the other hand, the major advantage of plasma discharge technique is in the possibility of using several facilities in parallel to increase the yield of nanoparticles. Spark-based methods allow formation of very small nanoparticles in gas-phase, whereas much larger nanoparticles can be formed by using arc discharges.
To better understand and to optimize these processes, detailed numerical modeling is performed. The involved stages are considered and analyzed.
The resulting nanoparticle parameters are investigated as a function of the experimental conditions. Nanoparticle properties, such as mean size and mean concentration are analyzed. Differences and similarities between the considered synthesis methods are discussed. Optimal experimental conditions are furthermore suggested based on the resulted nanoparticle characteristics in agreement with several previous experiments.
9737-2, Session 1
Haeyeon Yang, Anahita Haghizadeh, South Dakota School of Mines and Technology (United States)
Lateral semiconductor nanowires are typically fabricated by the selfassembly process that is driven by the strain-relaxation mechanism.
However, the nanowire dimensions – width, height, and length – are difficult to control. We have observed semiconductor nanowires from the surfaces when they are irradiated by high power laser pulses interferentially. The narrowest nanowires observed have the width smaller than 20 nm from
GaAs surfaces, which is more than 10 times smaller than the interference period while the smallest width of nanowires from the Si(001) surface is about 50 nm, which is larger than that from GaAs but still more than four times smaller than the interference period used. Furthermore, the dimensions depend on the interferential parameters such as intensity and interference period. These nanowires form when the top surface atoms are selectively mobilized by transient thermal gratings, which are created on the surface by the interferential irradiation of high power laser pulses. We study impacts of the transient thermal grating on morphologies of nanowires on semiconductor surfaces. Strain-free, self-assembled nanodots as well as periodic nanowires are observed from Si and GaAs(001) surfaces when
9737-4, Session 1
(Invited Paper)
Masoud Mahjouri-Samani, Oak Ridge National Lab . (United
States); Mengkun Tian, The Univ . of Tennessee Knoxville
(United States); Ming Wei Ling, Andrew R . Lupini, Kai
Wang, Christopher M . Rouleau, Alexander A . Puretzky,
Gyula Eres, Ilia N . Ivanov, Kai Xiao, Oak Ridge National
Lab . (United States); Gerd Duscher, The Univ . of Tennessee
Knoxville (United States); David B . Geohegan, Oak Ridge
National Lab . (United States)
Two-dimensional layered semiconducting materials, particularly the metal chalcogenides, have recently attracted significant renewed attention due to the novel physical, chemical, electrical and optical properties.
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Developing new methods for controlled synthesis and manipulation of these layered materials is crucial for emerging applications in functional devices. Here we demonstrate the use of pulsed laser vaporization as a versatile method for the synthesis and processing of 2D layered semiconductors with controlled number of layers, crystallite size, growth location and composition. This PLV approach offers a new synthesis solution to address the challenges of conventional vapor phase growth methods
(e.g., CVD), by taking advantage of tunable kinetic energy of the lasergenerated precursors for formation of either atomic species in vacuum, or stoichiometric nanoparticles in background gases for the synthesis of various 2D layered materials. Utilizing the stoichiometric nanoparticles as feedstocks, we demonstrate the formation of either small domain nanosheet networks (~ 200 nm) or large crystalline domains (~100 µ m). High kinetic energy atomic species, on the other hand, are used in doping, alloying and formation of lateral heterojunction within monolayer 2D crystals. The synthesis and conversion processes are further studied by Raman and photoluminescence spectroscopy, atomically resolved scanning transmission electron microscopy, as well as by fabrication and characterization of simple optoelectronic devices. These novel laser-based synthesis and processing approaches enable the controlled synthesis and manipulation of 2D layered semiconductors for ultrathin optoelectronics and devices.
Research sponsored by the U.S. Dept. of Energy, Office of Science, Basic
Energy Sciences, Materials Science and Engineering Div. (synthesis science) and Scientific User Facility Div. (characterization science).
9737-5, Session 2
(Invited Paper)
Irina N . Zavestovskaya, P .N . Lebedev Physical Institute
(Russian Federation)
No Abstract Available
Conference 9737:
Synthesis and Photonics of Nanoscale Materials XIII pulse energy, scan speed and scan line separation) have been explored with view on the possible influence of thermal accumulation and geometrical factors on the homogeneous propagation of the sub-wavelength structure over macroscopic regions. The best results in terms of modulation amplitude and homogeneous extension of the LIPSS orientation are observed for the scanning direction perpendicular to the polarization axis. Optimal, large area (~10 cm^2) surface structures in Cr can be produced in a few minutes showing relative diffraction efficiencies up to ~40%. The processing strategy is robust in terms of broad parameter windows and applicable to other materials.
9737-7, Session 2
Sho Itoh, Nippon Electric Glass Co ., Ltd . (Japan) and Kyoto
Univ . (Japan); Masaaki Sakakura, Yasuhiko Shimotsuma,
Kiyotaka Miura, Kyoto Univ . (Japan)
Several applications of glass nanofibers have been proposed for the past years. We found a method for fabricating nanofibers with a diameter of
100 nm order from thin glass substrates using a nanosecond pulsed UV
355 nm laser. In the latest report, we studied the generation process of nanofibers, which showed that voids were formed in the substrate during laser irradiation, and then materials seemed to be pushed from the back surface. However, the details of the generation mechanism have not become clear. Here, we focused on the behavior of ejection of the material, and investigated the reason for nanofiber generation. According to the high-speed camera images taken by synchronizing to the laser oscillator, we confirmed that molten glass was ejected from the back surface of substrates. To simplify the process, we conducted irradiation to substrates without scanning the laser beam. As a result, when focusing location was set below the back surface, glass was cracked, caused by heat generated around the irradiated area along with drilling. Thus, we considered that nanofibers were generated from the ejected molten glass, which was caused by heating and drilling through the molten part of substrates by the pulsed laser. We will also present a possible mechanism for the driving force of pushing the molten part from glass substrate. Understanding the mechanism leads to the process control of glass nanofiber fabrication.
9737-6, Session 2
Daniel Puerto, Jan Siegel, Instituto de Óptica “Daza de
Valdés” (Spain); Ruth Lahoz, Instituto de Ciencia de
Materiales de Aragón (Spain); Javier Hernandez-Rueda,
Univ . of California, Davis (United States); Alexandro Ruiz de la Cruz, Instituto de Óptica “Daza de Valdés” (Spain);
Xerman F . de la Fuente, Instituto de Ciencia de Materiales de Aragón (Spain); Javier Solis, Instituto de Óptica “Daza de Valdés” (Spain)
9737-8, Session 2
Alexandr A . Antipov, Sergey M . Arakelyan, Vladimir State
Univ . (Russian Federation); Yury V . Ryabchikov, Ahmed
Al-Kattan, Andrei V . Kabashin, Aix-Marseille Univ . (France) and Lasers, Plasmas et Procédés Photoniques (France);
Stella V . Kutrovskaya, Alexey O . Kucherik, Vladimir State
Univ . (Russian Federation); Tatiana E . Itina, Lab . Hubert
Curien (France)
The formation of Laser-Induced Periodic Surface Structures (LIPSS) is a universal phenomenon that has been observed in a wide variety of materials. It is generally accepted that LIPSS formation relates to the interference of the incident beam with a surface wave (scattered or induced) in a process greatly conditioned by the transient complex refractive index of the strongly excited material. In metals, electron-phonon coupling, plasma density and electron diffusion have been identified as important parameters for LIPSS formation at low fs-laser repetition rates.
In this work we report on the unique characteristics of low spatial frequency
LIPSS in Cr and other materials upon high repetition rate, fs-laser beam scanning irradiation. Highly regular, large area patterns with sub-wavelength period can be produced for a wide range of repetition rates (100´s kHz range), over large areas (~cm^2) and high scan speeds (~m/s). Different irradiation conditions (laser repetition rate, wavelength, beam polarization,
Gold nanoparticles (Au NPs) attract particular attention because of their unique size-dependent chemical, physicochemical and optical properties
[1-2] and, hence, their potential applications in catalysis, nanoelectronics, photovoltaics and medicine. In particular, laser-produced colloidal nanoparticles [2-3] are known to be not only bio-compatible, but also reveal unique chemical properties. In addition, different laser systems can be used for synthesis of these colloids, varying from continuous wave (CW) to ultra-short femtosecond lasers. However, despite rapidly growing interest in laser-based synthesis techniques, the choice of laser system is still not clear enough for concrete applications. To bring more light at this issue,
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9737-9, Session 2
Andrei V . Kabashin, Lasers, Plasmas et Procédés
Photoniques (France)
No Abstract Available
Conference 9737:
Synthesis and Photonics of Nanoscale Materials XIII we investigate an influence of laser parameters on a gold target immersed in deionized water. First, diagnostics of CW laser-induced hydrodynamic processes close to gold surface is performed. It is shown that gas bubbles do not form during continuous laser heating. Gold nanoparticle colloids with average size 7–8 nm and narrow size distribution (3–5 nm) owing to CW laser ablation are formed. The obtained results are compared with the ones obtained by using the second harmonics and with previous results obtained by using femtosecond laser systems.
[1] Mafuné F, Kohno J Y, Takeda Y and Kondow T 2000 J. Phys. Chem. B 106
7575–7577
[2] Maximova K, Aristov A and Kabashin A V 2015 Nanotechnol. 26 065601
[3] Sylvestre J P, Kabashin A V, Sacher E and Meunier M M 2005 Appl. Phys.
A 80 753–758 ISSN 0947-8396 electrons (plasmons), nanoplasmonics offers two modalities for biosensing:
(i) optical transduction, which detects changes in the refractive index of a dielectric medium adjacent to a gold nanostructure resulting from a binding event between a target analyte (antigens, DNAs etc.) and its corresponding receptor (antibodies etc.); (ii) Surface Enhanced Raman Scattering (SERS), which employs the effect of electric field enhancement near noble metal nanostructures to drastically enhance Raman scattering and thus detect trace amounts of biomaterials. A huge upgrade of current state-of-the-art plasmonic biosensing technology is now expected from the employment of novel sensing-oriented plasmonic metamaterials, or artificial materials composed of noble metal nanoblocks with nanoscale distance between them, which could provide new sensing principles/properties in order to radically improve sensing response [1,2]
This presentation will describe metamaterial architectures, which can combine ultrasensitive optical biosensing with SERS-based recognition functionality. Such metamaterials are based on gold nanodot-based dimers arranged in a periodic lattice. We show that such structures can provide extremely high phase sensitivity to refractive index variations due to the excitation of localized plasmon resonances [2]. On the other hand, a strong enhancement of electric field between nanodot dimer structures makes possible the implementation of parallel Surface Enhanced Raman Scattering and Surface Enhanced Fluorescence channels. By modifying Aperture-less
SNOM technique based on a standard Ntegra Spectra system (NT-MDT), we map evanescent plasmonic field distribution near golden nanoparticles and in the gaps between the nanoparticles (hot spots) in order to optimize nanoarchitectures for hybrid sensing platforms.
[1] Kabashin, A. V. et al. Nature Mater., 2009, 8, 867-871
[2] Kravets, V. G. et al. Nature Mater. 2013, 12, 304-309
9737-10, Session 3
(Keynote
Presentation)
Sasha Grigorenko, The Univ . of Manchester (United
Kingdom)
9737-13, Session 3
Mohammad Reza Aziziyan, Jan J . Dubowski, Univ . de
Sherbrooke (Canada)
We discuss creation and operation of hybrid graphene-plasmonic waveguide modulators in which graphene is used to achieve on-chip processing of information. We consider several promising hybrid configurations, debate the importance of mode field configuration and geometry of waveguides for achieving high modulation depth and identify the most promising hybrid devices for telecom applications. Various working graphene-plasmonic modulators will be presented and compared with state-or-the art silicon modulators. Our proof-of-concept results pave the way towards on-chip realization of efficient graphene-based active plasmonic waveguide devices for optical communications.
9737-11, Session 3
(Invited Paper)
Edik U . Rafailov, Aston Univ . (United Kingdom)
No Abstract Available
Nowadays, research focused on the development of rapid and low cost biosensing platforms is vastly increasing in response to the demand of numerous consecutive tests in the health sector. Different transducers have been investigated for detection of bacteria in aqueous solutions, addressing the need of controlling the level of bacteria in water, where large number of repeated tests is necessary. In that respect, biosensing based on photoluminescence of GaAs/AlGaAs heterostructures has been studied due to the promise of being a precise, fast and low cost diagnostic tool. However, bacteria adhesion studies have shown that electrical double layer repulsion of transducer surface can drive back bacteria immobilization process, resulting in restricted detection limit. We have investigated this effect using a 3-electrode fluidic setup, and applied potential measured against Ag/AgCl reference electrode. We demonstrate that electrically biased GaAs/AlGaAs heterostructures experience modulation of their band bending, which can lower this repulsion and result in improved bacteria immobilization. Changing band bending through electrical bias can vary the space charge region and alter conditions of a semiconductor interacting with electrically charged molecules. Whenever band bending is lowered the surface charge will decrease and so the double layer repulsion force. Hence, more amount of bacteria could approach the surface of GaAs and attach to it. Our results have shown that applying a 20 mV bias can double the surface coverage with bacteria.
9737-12, Session 3
Artem Danilov, Aix-Marseille Univ . (France)
Based on the unique property of noble metals to support oscillations of free
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9737-14, Session 3
Conference 9737:
Synthesis and Photonics of Nanoscale Materials XIII
Yury V . Ryabchikov, Aix-Marseille Univ . (France) and P .N .
Lebedev Physical Institute (Russian Federation); Anton
Popov, Aix-Marseille University (AMU) (France); Ronan Le
Dantec, Savoie University, SYMME Laborotary, 7 chemin de Bellevue, 74940 Annecy-le-Vieux, France (France);
Vladimir Lysenko, Institut des Nanotechnologies de Lyon
(France); Victor Y . Timoshenko, Lomonosov Moscow
State Univ . (Russian Federation); Andrei V . Kabashin, Aix-
Marseille Univ . (France)
A technique of femtosecond laser ablation and fragmentation in pure deionized water was used to synthesize hybrid semiconductor-metal nanoparticles (Au-Si, Au-C etc). Depending on conditions of laserablative synthesis, the nanostructures had different nano-architectures such as hybrid aggregates or core-shells. Such hybrid structures could exhibit interesting optical properties, including enhanced absorption and photoluminescence. Based on excellent biocompatibility of constituents, the nanostructures present a novel, extremely promising object for biological imaging and therapy.
9737-17, Session 4
Daniel C . Mayo, Vanderbilt Univ . (United States); Ryan
Nolen, Lipscomb Univ . (United States); Andrew Cook,
Richard Mu, Fisk Univ . (United States); Richard F . Haglund
Jr ., Vanderbilt Univ . (United States)
Conventional scintillation detectors are single crystals of heavy-metal oxides or halides doped with rare-earth ions that report the recombination of electron-hole pairs by photon emission in the visible to ultraviolet.
However, the light yields are typically low enough to require photomultiplier detection with the attendant instrumental complications. Here we report the first studies of gamma ray detection by large-area arrays of zinc oxide nanowires, grown by vapor-solid deposition. The nanowires grow along the c-axis in a wurtzite structure; they are typically 100 nm in diameter and have lengths of 1-2 µ m. The nanowires are single crystals of high quality, with a photoluminescence (PL) yield from band-edge exciton emission in the ultraviolet that is typically one hundred times larger than the PL yield from defect centers in the visible. Nanowire ensembles were irradiated by
662 keV gamma rays from a Cs-137 source for up to ten hours; gamma rays in this energy range interact by Compton scattering, which in ZnO creates
F+ centers that relax to form singly-charged positive oxygen vacancies.
Following irradiation, we fit the PL spectra of the visible emission with a sum of Gaussians at the energies of the known defects. Over a period of days, the singly charged O vacancies relax to the more stable doubly charged O vacancies. However, the overall defect PL returns to pre-irradiation values after about a week, as the vacancies diffuse to the surface of these very thin nanowires, thus indicating that a self-annealing process restores the nanowires to their original state.
9737-15, Session 4
(Invited Paper)
Vladislav V . Yakovlev, Texas A&M Univ . (United States)
No Abstract Available
9737-16, Session 4
Abdelaziz Boulesbaa, Bing Huang, Kai Wang, Ming-Wei
Lin, Masoud Mahjouri-Samani, Christopher M . Rouleau, Kai
Xiao, Mina Yoon, Bobby G . Sumpter, Alexander A . Puretzky,
David B . Geohegan, Oak Ridge National Lab . (United
States)
9737-18, Session 4
Alexander A . Puretzky, Liangbo Liang, Xufan Li, Kai Xiao,
Kai Wang, Masoud Mahjouri-Samani, Oak Ridge National
Lab . (United States); Leonardo Basile, Escuela Politécnica
Nacional (Ecuador); Juan Carlos Idrobo, Bobby G .
Sumpter, Oak Ridge National Lab . (United States); Vincent
Meunier, Rensselaer Polytechnic Institute (United States);
David B . Geohegan, Oak Ridge National Lab . (United
States)
Recently, trions emerged as new three-body quasiparticles in atomically thin two dimensional (2D) materials. Here, we present the observation of two distinct negative trions T1 and T2 in tungsten disulfide monolayers (2D-WS2) on a sapphire substrate. Ultrafast pump-probe spectroscopy measurements indicated that two band-edge excitons, XA and XB, generated by the pump laser dissociated through hole trapping by the substrate, defects, or adsorbates, which rendered the material n-doped and resulted in new trionic transitions. Upon absorption of the probe laser photons, the generated electron-hole pairs joined the photo-doped electrons to form T1 and T2. Pumping with different photon energies followed by femtosecond white-light continuum probe revealed two different induced absorption peaks that can be assigned to two different trions, T1 and T2. The possible mechanism of this trion formation will be discussed. This finding highlights the important role of defects and substrates in defining optical and electrical properties of 2D metal chalcogenides.
Stacked monolayers of two-dimensional (2D) materials present a new class of hybrid materials with tunable optoelectronic properties determined by their stacking orientation, order, and atomic registry. Here we report measurements and ab initio calculations of low frequency Raman shear and breathing modes in few layer MoSe2 synthesized by chemical vapor deposition with a variety of natural layer stackings and also stamped together with an arbitrary twist angle. We showed that the low frequency
(LF) Raman modes (< 50 cm-1) that originate from interlayer vibrations can serve as ‘fingerprints’ to characterize not only the number of layers, but also their stacking configurations. Moreover, we showed how the low frequency shear and breathing modes evolve in twisted two-layer (2L)
MoSe2 depending on the twist angle. The observed Raman spectra and their dependence on stacking configurations were interpreted using ab initio calculations of the frequencies and intensities. The low frequency modes in
TMDs provide a powerful tool for understanding interlayer interactions and designing heterostuctures based on stacking of different TMD layers.
Synthesis science was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering
Division. Characterization and computational science at CNMS was supported by the Scientific User Facilities Division, BES.
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9737-19, Session 5
Haeyeon Yang, Anahita Haghizadeh, South Dakota School of Mines and Technology (United States)
Epitaxial nanodots are typically fabricated by the so-called Stranski-
Krastanov growth technique, which is an energy minimization process driven by the relaxation of accumulated strain energy. This process can results in high density quantum dots for energy related devices such as intermediate band solar cells because it is crucial to have high density nanodots for this and other optoelectronic device applications. However, large cluster defects begin to show up as the dot density is increased over the certain value, a critical density of about 7x1010 dots/cm2, over which the increase in dot density does not increase the performance of solar cells. We report a higher dot density than the critical value without formation of large clusters. These dots are observed from the GaAs(001) surfaces when they are irradiated interferentially by high power laser pulses of 7 ns. The laser wavelength used are 532, 355, and 266 nm. The dot density and morphology depend on the laser intensity and interference parameters such as wavelength and interference angle. The morphology of dots are examined by atomic force microscopy while their stoichiometry is characterized by energy dispersive electron spectroscopy in a field effect scanning electron microscope. The chemical analysis suggests that quality nanodots can be fabricated by irradiation of high power laser pulses on surfaces. Furthermore, these dots are strain-free so that the strain is not necessary anymore to fabricate quality nanodots.
9737-20, Session 6
Conference 9737:
Synthesis and Photonics of Nanoscale Materials XIII
Anton Rudenko, Jean-Philippe Colombier, Tatiana E . Itina,
Lab . Hubert Curien (France)
We investigate femtosecond laser irradiation of dielectric materials containing randomly distributed nano-defects. For this, numerical modeling is performed based on a solution of Maxwell equations together with kinetic equations for free electron excitation/relaxation processes. The processes of electron plasma generation due to both multiphoton and avalanche ionization are studied in fused silica in the presence of nanoparticles and/or nano-holes. In particular, light propagation is analyzed as a function of the defect size and density. The performed calculations show that the generated free electron plasma significantly depends of the defect density and on laser wavelength. The resulted distribution of the electromagnetic field and the following thermo-mechanical effects are examined and compared with the available experimental findings. The study can help in the evaluation of the damage threshold of such materials and allow a better control over laser nanomachining. Recent results have furthermore shed light on such effects as femtosecond laser-assisted volume nanograting formation previously observed in several dielectric materials [1,2]. The periodicity and the quality of the produced nanoplanes are found to strongly depend on the concentration of the initial defects and on the irradiation wavelength.
[1] Kazansky P. et al., “”Quill” writing with ultrashort light pulses in transparent materials”, Appl. Phys. Lett., Vol. 90, 151120, 2007
[2] Taylor R., “Application of femtosecond laser induced self-organized planar nanocracks inside fused silica glass”, Laser & Photon. Rev. 2, No. 1-2,
26-46, 2008
9737-21, Session 6
David B . Geohegan, Masoud Mahjouri-Samani, Oak Ridge
National Lab . (United States); Mengkun Tian, The Univ . of Tennessee (United States); Gerd Duscher, The Univ . of
Tennessee Knoxville (United States); Gyula Eres, Alexander
A . Puretzky, Christopher M . Rouleau, Mina Yoon, Oak Ridge
National Lab . (United States)
The formation, pulsed laser deposition (PLD), and transformation of ultrasmall amorphous TiO2 nanoparticles into photosensitive core-shell
TiO2/Ti2O3 crystalline nanoparticles (“black TiO2”) is reported. First, timeresolved in situ plume diagnostics are used to understand the conditions for the PLD of films consisting of pure, ultrasmall nanoparticles (UNPs, ~
3 nm) in mesoporous architectures by laser ablation of TiO2 targets and condensation in low-pressure background gases. We describe an interesting regime where nanoparticles formed within the decelerating plasma plume propagate past it – answering a longstanding question in PLD. Second, these ultrasmall, amorphous TiO2 nanoparticles are then investigated as tunable
“building blocks” for catalyst-free transformation into larger nanostructures or films with metastable crystalline phases. With increasing substrate temperature the UNPs are shown to integrate into nanowires, nanosheets, or vertically-oriented crystalline nanorods, sometimes with unusual metastable phases (e.g., TiO2(B), and “black TiO2”). Theory and simulation, along with state-of-the-art atomic-resolution Z-contrast scanning transmission electron microscopy, nano-beam electron diffraction (NBED), and electron energy loss spectroscopy (EELS), indicate that the evolution of a particular crystalline phase and preferred growth orientation is linked to the defects and ordering of TiO6 octahedral units within each metastable amorphous nanoparticle. We focus on the formation of “black TiO2”, a remarkable variant of TiO2 relevant to hydrogen production by photocatalytic water splitting. We discuss the generality of the technique to the formation of a variety of phases and nanostructure morphologies (of various materials) by alteration of the processing conditions.
Research sponsored by the U.S. Dept. of Energy, Office of Science, Basic
Energy Sciences, Materials Science and Engineering Div. (synthesis science) and Scientific User Facilities Div. (characterization science).
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9738-1, Session 1
Ryota Kojima, Hiroshi Ikenoue, Masaru Suwa, Akihiro
Ikeda, Daisuke Nakamura, Tanemasa Asano, Tatsuo Okada,
Kyushu Univ . (Japan)
We have proposed a novel method of low-temperature nitrogen doping into 4H-SiC(0001) induced by KrF excimer laser irradiation to a SiNx film.
The SiNx film with a thickness of 100 nm was deposited on an n-type
4H-SiC(0001) substrate by chemical vapor deposition. Laser beam size on the sample surface was 300 ?m?300 ?m. Irradiation fluence was 1.0 J/ cm2-4.0 J/cm2, and the number of shots was from 1 shot to 30 shots.
Laser irradiation was performed in a vacuum chamber to avoid oxidation of the SiC surface. High concentration nitrogen doping (~1?1020 /cm3 at the surface) and very low contact resistance with ohmic I-V characteristics can be achieved by laser ablation of the SiNx film. In the case of laser irradiation of 1.5 J/cm2 and above 5 shots, the SiNx film was almost ablated without laser ablation of the SiC substrate. Then, excellent ohmic contact characteristics was obtained at the irradiation number of 5 shots, and it was hardly deteriorated up to 30 shots. In the case of irradiation fluence above
2.5 J/cm2, ablation of the SiC substrates was induced and ohmic contact characteristics were deteriorated with increasing the number of shots. From these results, we conclude that excellent ohmic contact characteristics without irradiation damage to SiC substrates can be obtained in a stable at the irradiation fluence of 1.5 J/cm2.
9738-3, Session 2
Paul Delrot, Miguel A . Modestino, Demetri Psaltis,
Christophe Moser, Ecole Polytechnique Fédérale de
Lausanne (Switzerland)
Drop-on-demand inkjet printing is mostly based on thermal and piezoactuation, allowing for densely packed nozzles in inkjet printers. However, the droplet diameter is typically defined by the nozzle diameter, thus limiting the range of viscosity that can be jetted to 10-100 mPa.s to prevent nozzle clogging. Here, we present a laser-assisted system for the delivery of micro-droplets of highly viscous fluids with sub-nozzle resolution. Highly focused supersonic jets have recently been demonstrated by focusing a nanosecond pulse of light into a micro-capillary filled with dyed water, hence generating a cavitation bubble. The consequent pressure wave impact on the concave free surface of the liquid generated flow-focused micro-jets.
We implemented this technique for the production of low velocity microdroplets (1-4 m/s) with photopolymer inks of increasing viscosity (0.6-148 mPa.s) into a 430 µ m-wide glass capillary using low laser energies (3-70
µ J). Time-resolved imaging provided details on the droplet generation.
Single micro-droplets of diameter 70-80 µ m were produced on demand with inks of viscosity 0.6-9 mPa.s with good controllability and reproducibility, thus enabling to print two-dimensional patterns with a precision of 13 µ m. Furthermore, the primary droplet produced with the most viscous fluid was less than half of the capillary diameter. Preliminary results also showed that the process is linearly scalable to narrower capillaries (100-200 µ m), thus paving the way for a compact laser-assisted inkjet printer. A possible application of the device would be additive manufacturing as the printed patterns could be consequently cured.
9738-2, Session 1
Jie Liu, Lei Yuan, Clemson Univ . (United States); Jie Huang,
Missouri Univ . of Science and Technology (United States);
Hai Xiao, Clemson Univ . (United States)
Optical fiber based acoustic pressure sensors have attracted more and more interests in recent years due to their small sizes, light weight, large young’s modulus, and immunity to electromagnetic interference. Various optical fiber structures have been investigated in/on fiber tips for acoustic sensing such as a thin-film diaphragm, a sealed cavity, a Bragg grating structure, and a micro/nano periodic structure, etc. Among these structures, femtosecond
(fs) laser micromachining has been a promising mean for fabrication of micro/nano structures in/on optical fiber tips attributed to its high precision, flexible design, assembly free, and compatible with other methods such as sputtering coating, fusion splicing, etc.
In this paper, we present a pure silica micro-cantilever based optical fiber sensor for acoustic pressure detection. The cantilever is directly fabricated by fs laser micromachining on an optical fiber tip functioning as an inline
Fabry-Perot interferometer (FPI). The applied acoustic wave pressurizes the micro-cantilever beam and the corresponding dynamic signals can be probed by the FPI. The thickness, length, and width of the micro-cantilever beam can be flexibly designed and fabricated so that the sensitivity, frequency response, and the total measurement range can be varied to fit many practical applications. Experimental and simulation results with various designs will be presented and analyzed. Due to the assembly free fabrication of the fs-laser, multiple micro-cantilever beams could be potentially fabricated in/on a single optical fiber for quasi-distributed acoustic mapping with high spatial resolution.
9738-4, Session 2
(Invited Paper)
Johannes Pröll, Karlsruher Institut für Technologie
(Germany); Heungsoo Kim, U .S . Naval Research Lab .
(United States); Yijing Zheng, Peter Smyrek, Hans J .
Seifert, Karlsruher Institut für Technologie (Germany);
Alberto Piqué, U .S . Naval Research Lab . (United States);
Wilhelm Pfleging, Karlsruher Institut für Technologie
(Germany)
Recently, three-dimensional (3D) electrode architectures have attracted great interest for the development of lithium-ion micro-batteries applicable for Micro-Electro-Mechanical Systems (MEMS), sensors, and hearing aids.
Since commercially available micro-batteries are mainly limited in overall cell capacity by their electrode footprint, new processing strategies for increasing both capacity and electrochemical performance have to be developed. In case of standard micro-batteries, two-dimensional (2D) electrode arrangements are applied with thicknesses up to 200 µ m.
These electrode layers are composed of active material, conductive agent, graphite, and polymeric binder. Nevertheless, with respect to the type of active material, the active material to conductive agent ratio, and the film thickness, such thick-films suffer from low ionic and electronic conductivities, poor electrolyte accessibility, and finally, limited electrochemical performance under challenging conditions. In order to overcome these drawbacks, 3D electrode arrangements are
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Conference 9738: Laser 3D Manufacturing III under intense investigation since they allow for the reduction of lithiumion diffusion pathways in between interdigitated electrodes, even for electrodes with enhanced mass loadings. In this paper, we present how to combine laser-printing and femtosecond laser-structuring for the development of advanced 3D electrodes composed of LiFePO4 (LFP) and
LiNi1/3Mn1/3Co1/3O2 (NMC). In a first step, LFP and NMC thick-films were laser-printed and calendered to produce film thicknesses in the range of 30
µ m - 200 µ m. In a second step, femtosecond laser-structuring was carried out to form 3D architectures directly into thick-films. Finally, electrochemical cycling of laser-processed films was performed in order to evaluate the most promising 3D electrode design suitable for application in long life-time
3D micro-batteries.
9738-5, Session 5
(Invited
Paper)
Martin F . Schumann, Karlsruher Institut für Technologie
(Germany); Samuel Wiesendanger, Friedrich-Schiller-Univ .
Jena (Germany); Jan Christoph Goldschmidt, Benedikt
Bläsi, Fraunhofer-Institut für Solare Energiesysteme
(Germany); Karsten Bittkau, Ulrich W . Paetzold,
Forschungszentrum Jülich GmbH (Germany); Alexander N .
Sprafke, Martin-Luther Univ . Halle-Wittenberg (Germany);
Ralf B . Wehrspohn, Martin-Luther Univ . Halle-Wittenberg
(Germany) and Fraunhofer-Institut für Werkstoffmechanik
(Germany); Carsten Rockstuhl, Martin Wegener, Karlsruher
Institut für Technologie (Germany)
Metallic contact fingers on the sun-facing side of solar cells are necessary to reduce Ohmic losses but also represent optically dead regions reducing the energy conversion per area. In this talk, we present two approaches to solve this problem by “cloaking the contacts”. The first approach uses graded-index metamaterials designed by two-dimensional Schwarz-
Christoffel conformal maps, the second free-form surfaces designed by one-dimensional coordinate transformations. We provide proof-of-principle demonstrators using direct laser writing of polymer structures on silicon wafers with opaque metal contacts. Using the so-called shell-writing mode, fabrication times for “masters” are reduced significantly, potentially enabling mass fabrication via imprinting. We show that the free-form-surface approach completely solves the shadowing problem for all relevant angles of incidence, all polarizations, and colors of sunlight for contact coverages up to about 20%. Typical present coverages are below 10%. Moreover the free-form approach is amenable to mass fabrication by making a “master” by direct laser writing and then using this “master” for printing. Due to the special shape of the free-form surface, the required micrometer dimensions, and the necessary surface smoothness, direct laser writing is presently the only possible means for fabricating the “master”.
high electrical conductance and strength is still a long-standing challenge.
In this work, TPP fabrication of arbitrary 3D micro/nanostructures using multi-walled carbon nanotube (MWNT)-acrylate composite resins has been developed. Up to 0.2 wt% MWCNTs have been incorporated into thiolacrylate resins to form highly uniform and stable composite photoresists without obvious degradation for one week at room temperature. Various functional 3D micro/nanostructures including woodpiles, microcantilevers, suspended microbridges, microcoil arrays, and complex microcars have been successfully fabricated by TPP and characterized by scanning electron microscopy, Raman spectroscopy, and fluorescence spectroscopy.
Comparing with conventional acrylate based resins, the MWNT-acrylate composite resin offers significant enhancements in electrical conductivity
(from insulating polymer to conductive composite, 2?103 S/m) and mechanical strength (2.08 GPa in reduced Young’s Modulus, 1.3-fold enhancement; 113 KPa in hardness, 1.7-fold enhancement), and at the same time, preserving a high optical transmittance (95 % at 550 nm for 3 um film) and flexibility. The micro/nanofabrication technique based on the MWNTacrylate composite resins enables the precise fabrication of arbitrary 3D micro/nanostructures of high conductivity, strength, and low shrinkage, which promises a wide range of device applications, including MEMS/NEMS,
3D electronics, integrated optics, biomimetics, and metamaterials.
9738-7, Session 5
Andrew R . Bañas, OptoRobotix ApS (Denmark); Jesper
Glückstad, Technical Univ . of Denmark (Denmark)
Generalized Phase Contrast (GPC) is a light efficient method for generating speckle-free contiguous optical distributions using binary-only or analog phase levels. GPC has been used in applications such as optical trapping and manipulation, active microscopy, structured illumination, optical security, parallel laser marking and recently in contemporary biophotonics applications such as for adaptive and parallel two-photon optogenetics and neurophotonics. We will present our most recent GPC developments geared towards these applications. First, a compact GPC Light Shaper implementation based on our latest theoretical derivations is used to demonstrate the benefits for typical applications where lasers have to be actively shaped into particular light patterns. We then show the potential of
GPC for biomedical and multispectral applications where we experimentally demonstrate the active light shaping of a supercontinuum laser over most of the visible wavelength range. Finally, we demonstrate how GPC can be advantageously applied for fully parallel and non-scanning Laser Direct
Writing of 3D structures using two-photon excitation pulsed laser sources.
9738-6, Session 5
Ying Liu, Wei Xiong, Li Jia Jiang, Yunshen Zhou, Yongfeng
Lu, Univ . of Nebraska-Lincoln (United States)
Two-photon polymerization (TPP) is of increasing interest due to its unique combination of truly 3D fabrication capability and ultrahigh spatial resolution of ~100 nm. However, the stringent requirements of non-linear resins seriously limit the material functionality of 3D printing via TPP. Precise fabrication of 3D micro/nanostructures with multi-functionalities such as
9738-8, Session 6
(Invited Paper)
Jesper Glückstad, Technical Univ . of Denmark (Denmark)
The 2014 Nobel Prize on nanoscopy has cemented that optics is a key enabling technology for getting a grasp of the micro- and nano-world. By creatively combining a host of complementary approaches one can today realize advanced optical modalities that integrate an increasing number of functionalities and augment not just passive observation but also active access and control over the nanoworld. Using a merger of light and matter sculpting, we have laser-fabricated free-floating waveguides that can be optically trapped and remote-controlled in a volume; hence coined Waveguided Optical Waveguides (WOWs). Combining 3D laser-based microfabrication with 3D optical trapping and manipulation allows us to exploit these WOWs in versatile and dynamically reconfigurable architectures. A plurality of counter-propagating beam-traps relayed to the trapping volume by low-NA microscope objectives on our Biophotonics Worskstation (BWS) control the WOW-structures demonstrating the possibility for a structuremediated paradigm where micron-sized tools are used to achieve optical near-field tip-size access in 3D. However, realizing the full potential of this
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Conference 9738: Laser 3D Manufacturing III new structure-mediated approach in challenging microscopic geometries requires a versatile 3D light coupling that can dynamically track a plurality of WOWs to ensure continuous optimal light probing.
9738-9, Session 6
Cleber R . Mendonça, Nathália B . Tomazio, Franciele
Henrique, Adriano J . G . Otuka, Juliana M . P . Almeida,
Instituto de Física de São Carlos (Brazil); Carla R . Fontana,
Univ . Estadual Paulista “Júlio de Mesquita Filho” (Brazil)
Femtosecond laser microfabrication has been shown to be a powerful tool for manufacturing advanced materials, aiming at applications from photonics to biology. The nonlinear nature of the light-mater interaction, achieved with fs-pulses, confines the induced changes to the focus of the laser, which has allowed the fabrication of complex three-dimensional microstructures. fs-microfabrication methods have been used to produce photonic crystals, waveguides, micromechanical actuators, scaffolds for biological applications, etc. Most of the microstructures reported, however, are passive elements, whose properties are not usually changed by external means. In this direction, our work has been focused on the development of strategies to produce functional microstructures by fs-laser fabrication methods. In this work we present results on the fabrication of light emitting devices, waveguides containing metal nanoparticles, micro-optical storage devices and microstructures for biological applications, using either multiphoton lithography or fs-laser micromachining. Results on the optical, mechanical and bio-related properties will be presented, which indicate the approach proposed as a promising tool for the development of applications from displays to tissue engineering. The authors acknowledge FAPESP
(2011/12399-0), CNPq, CAPES and the Air Force Office of Scientific Research
(FA9550-12-1-0028) for financial support. material will open a wider range of exciting applications.
[1] Abargues, R., Rodriguez-Canto, P. J., Garcia-Calzada, R. and J. Martinez-
Pastor, „Patterning of Conducting Polymers Using UV Lithography: The in-Situ Polymerization Approach“, J. Phys. Chem. C 116, 17547–17553 (2012).
[2] Jiguet, S., Bertsch, A., Hofmann, H. and Renaud P., „Conductive SU8
Photoresist for Microfabrication“, Adv. Funct. Mater. 15, 1511–1516 (2005).
[3] Benlarbi, M., Blum, L. J. and Marquette, C. A., „SU-8-carbon composite as conductive photoresist for biochip applications“, Biosens. Bioelectron. 38,
220–225 (2012).
[4] Hauptman, N., Zveglic, M., Macek, M. and Gunde M. K., „Carbon based conductive photoresist“, J. Mater. Sci. 44, 4625–4632, (2009).
[5] Annaiyan, U. M., Kalantar-zadeh, K., Fang, Q. and Cosic, I., “Development of a conductive photoresist with a mixture of SU-8 and HCL doped polyaniline”, Proc. IEEE Tencon 2005, 1B 07.2. (2005).
[6] Lu, W., Zhang, Y., Zheng, M., Jia, Y., Liu, J., Dong, X., Zhao, Z., Li, C.,
Xia, Y., Ye, T. and Duan, X., “Femtosecond direct laser writing of gold nanostructures by ionic liquid assisted multiphoton photoreduction”, Opt.
Mater. Express 3, 1660–1673 (2013).
[7] Bakhtina, N. A., Voigt, A., MacKinnon, N., Ahrens, G., Gruetzner, G.,
Korvink, J. G., Novel ionic liquid - polymer composite and an approach for its patterning by conventional photolithography, Proc. IEEE MEMS 2015, 97–101
(2015).
[8] Bakhtina, N. A., Loeffelmann, U., MacKinnon, N., Korvink, J. G., “Twophoton nanolithography enhances performance of an ionic liquid - polymer composite sensor”, Adv. Funct. Mater. 25, 1683-1693 (2015).
9738-10, Session 6
(Invited Paper)
Natalia A . Bakhtina, Neil MacKinnon, Jan G . Korvink,
Karlsruher Institut für Technologie (Germany)
A key challenge in micro- and nanotechnology is the direct patterning of functional structures. For example, it is highly desirable to possess the ability to create three-dimensional (3D), conductive, and optically transparent structures. Efforts in this direction have, to date, yielded less than optimal results since the polymer composites had low optical transparency over the visible range, were only slightly conductive, or incompatible with high resolution structuring.1-6 We have previously presented the novel crosslinkable, conductive, highly transparent composite material based on a photoresist (IP-L 780, OrmoComp, or SU-8) and the ionic liquid 1-butyl-
3-methylimidazolium dicyanamide.7-8 Material patterning by conventional and two-photon photolithography has been demonstrated as proof-ofconcept. Aiming to increase the resolution and to extend the spectrum of exciting applications we continued our research into identifying new ionic liquid - polymer composites. In this paper, we report the precise 3D singlestep structuring of ionic liquid - polymer nanostructures with excellent optical and electrical characteristics. This was achieved via the development of novel crosslinkable composite based on the photoresist IP-G 780 and the ionic liquid 1-butyl-3-methylimidazolium dicyanamide. The successful combination of the developed material with the advanced direct laser writing technique enabled the time- and cost-saving direct manufacturing of transparent, electrically conductive components with a resolution down to 150 nm. We believe that the excellent characteristics of the structured
9738-38, Session PTue
Bernd Reutterer, Lukas Traxler, Natascha Bayer, Andreas
Drauschke, Fachhochschule Technikum Wien (Austria)
Selective Laser Sintering (SLS) is considered as one of the most important additive manufacturing processes due to component stability and its broad range of usable materials. However the influence of the different process parameters on mechanical workpiece properties are still poorly studied, leading to the fact that further optimization is necessary to increase workpiece quality.
In order to investigate the impact of various process parameters, laboratory experiments are implemented to improve the understanding of the SLS limitations and advantages on an educational level.
Experiments are based on two different workstations, used to teach students the fundamentals of SLS. First of all a CO2 laser workstation is used to investigate the interaction of the laser beam with the used material in accordance with varied process parameters to analyze a single-layered test piece. Second of all the FORMIGA P110 laser sintering system from
EOS is used to print different 3D test pieces in dependence on various process parameters. Finally quality attributes are tested including warpage, dimension accuracy, surface quality or tensile strength. For dimension measurements and evaluation of the surface structure a telecentric lens in combination with a camera is used. A tensile test machine allows testing of the tensile strength and the interpreting of stress-strain curves.
The developed laboratory experiments are suitable to teach students the influence of processing parameters. In this context they will be able to optimize the input parameters depending on the component which has to be manufactured and to increase the overall quality of the final workpiece.
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Conference 9738: Laser 3D Manufacturing III
9738-41, Session PTue
Adriano Jose Galvani Otuka, Instituto de Física de São
Carlos (Brazil); Gustavo F . Almeida, Cleber R . Mendonça,
Univ . de São Paulo (Brazil)
Functionalized polymeric microdevices have been widely investigated in several technological researches. There are a wide range of materials which can be used to functionalize polymeric matrices. For instance, single walled carbon nanotubes (SWCNT) can promote mechanical improvement and enhance electrical properties of polymeric composites. Organic dyes can change optical properties of polymeric matrices, allowing selective fluorescence control from the ultraviolet to near-infrared. However, only a few studies have focused on the functionalization of polymers using different materials. In this work, we fabricated polymeric composites microdevices, functionalized with SWCNT and organic dyes, using multiphoton absorption polymerization. SWCNT functionalized with carboxylic acid were mixed to the liquid resin composed by equal proportions of two triacrylate monomers: tris(2-hydroxyethyl) isocyanurate triacrylate and ethoxylated(6) trimethylolpropane triacrylate. After this step, organic dyes, such as Rhodamine B or Disodium Fluorescein, are added to the SWCNTresin. To fabricate these structures, we use a Ti:sapphire laser (operating at 780 nm, 150 fs) focused through a microscope objective (0.85-NA) in the volume of the polymeric resin. The laser is scanned in the sample using a pair of galvanometric mirror (xy plan) and a motorized stage (z-axis).
Our results indicated changes in the mechanical properties of the sample containing SWCNT, such as in the elastic modulus and viscoelasticity.
Additionally, optical properties of the dyes were preserved in this fabrication method. The approach presented here is a promising alternative for functionalization of polymers, enabling the production of devices with special features for different fields.
9738-43, Session PTue
Da Liu, Chunyan Li, Beijing Institute of Control Engineering
(China); Fang Yin, BeiHang Univ . (China); Yi Li, Li Wang,
Beijing Institute of Control Engineering (China)
Laser point cloud registration is widely utilized in object 3D reconstruction and object measure. In the process, the point cloud from multiple laser scans in arbitrary initial position is identified and matched each other with corresponding rigid transforms.
In the paper, 4 to 6 key point are adaptive extracted from the point cloud according the character of the point cloud. Firstly, four key points are selected according to the surface area. Then the fifth and sixth point are selected according to the normal and cubage of all the key point. The four key point in the first step and six key point in the second step are separately utilized to shape matching. The match error of the four point and six point are calculated separately. If the difference of match error in four points and six points is less than a threshold, the match is terminated. Otherwise, the next key point is selected according to the normal and cubage of all the key point. The match error before and after the new added key points are calculated separately. If the difference of match error is less than a threshold, the match is terminated, otherwise a new key point is selected and added for match.
The robustness of the algorithm is demonstrated on several sets of multiple range scans with varying degree of noise and extent of overlap. The experimental results show that the proposed method is fast and robust, and are resilient to noise and outliers.
9738-42, Session PTue
Chenchu Zhang, Jingjing Zhang, Yanlei Hu, Jiawen Li,
Zhaoxin Lao, Ze Cai, Dong Wu, Jiaru Chu, Univ . of Science and Technology of China (China)
We demonstrate a maskless lithographic system to perform serial micropatterning based on two photon polymerization (TPP). We present a stage-shutter-free microfabrication approach to achieve arbitrary three dimensional (3D) micro structures without the use of 3D stage and shutter.
The Gerchberg-Saxton algorithm and a spatial light modulator (SLM) have been used to create and display phase holograms. The position of focus can be controlled by varying the phase holograms. However, some constraints such as phase quantization and dead space (those regions between pixels) will introduce undesired imperfection of the target patterns, especially foci nonuniformity, which will obviously affect the fabrication quality. An easy and efficient area-controlled approach is provided to increase the uniformity of focus in order to get 3D micro structures with higher quality. The dead space of SLM can be considered as a two dimensional (2D) grating, so that the desired multifoci pattern has an envelope of a 2D grating diffraction function, which elucidates the reason of uniformity reduction of the reconstruction pattern. Here we apply holograms with different active size based on the diffraction function of 2D grating to eliminate the nonuniformity of target focus. Several cubes are made and compared to optimize the fabrication parameters. In the end, a 3D Olympic Games logo was fabricated without moving stage and shutter, showing the promising application in cost reduction of 3D integrated TPP fabrication systems.
9738-44, Session PTue
Sankhya Mohanty, Jesper H . Hattel, Technical Univ . of
Denmark (Denmark)
Repeatability and reproducibility of parts produced by selective laser melting is a standing issue, and coupled with a lack of standardized quality control presents a major hindrance towards maturing of selective laser melting as an industrial scale process. Consequently, numerical process modelling has been adopted towards improving the predictability of the outputs from the selective laser melting process. Establishing the reliability of the process, however, is still a challenge, especially in components having overhanging structures.
In this paper, a systematic approach towards establishing reliability of overhanging structure production by selective laser melting has been adopted. A calibrated, fast, multiscale thermal model is used to simulate the single track formation on a thick powder bed. Single tracks are manufactured on a thick powder bed using same processing parameters, but at different locations in a powder bed and in different laser scanning directions. The difference in melt track widths and depths captures the effect of changes in incident beam power distribution due to location and processing direction. The experimental results are used in combination with numerical model, and subjected to uncertainty and reliability analysis.
Cumulative probability distribution functions obtained for melt track widths and depths are found to be coherent with observed experimental values.
The technique is subsequently extended for reliability characterization of single- and multiple layers produced on a thick powder bed without support structures, by determining cumulative probability distribution functions for average layer thickness, sample density and thermal homogeneity.
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Conference 9738: Laser 3D Manufacturing III
9738-45, Session PTue
Yuji Sato, Masahiro Tsukamoto, Osaka Univ . (Japan);
Yorihiro Yamashita, Industrial Research Institute of
Ishikawa (Japan); Shinichiro Masuno, Nobuyuki Abe, Osaka
Univ . (Japan)
Selective laser melting (SLM), one of an additive manufacturing technologies, is useful tools for direct and complicated shape formation.
We demonstrated that a Ti-6Al-4V plate, which is clinically used for artificial bone and hard tissue implant in humans because of their light and biocompatibility, were fabricated by SLM process in vacuum. The Ti64 powder has a spherical shape with a particle size distribution from 4 to
88 ?m. The chamber’s pressure was set to 1.0?10-2 Pa to prevent the Ti64 powder from oxidizing. The base plate of the powder bed was vertically dropped in determined steps, and Ti64 powder supplied from the powder feeder was then smoothed by a roller on top of the powder bed. The singlemode fiber laser irradiated and melted the powder bed to make a molten pool in order to form 2D metallic structures.
In order to investigate the laser melting and solidification dynamics, a process of Ti 64 plate fabrication (10mm x 10mm x1 mm) was captured by high speed video camera. It was also determined that crystal orientation was evaluated with X-ray diffraction (XRD) and energy dispersive X-ray
(EDX) spectroscopy. From EDX analysis, the chemical compounds were not changed from powder to fabricated sample. And it was recorded from the powder peaks of ? (1011), ? (0002), ? (1010), and ? (1012) that the crystal orientation is composed mainly of martensitic alpha by XRD. Diffraction peaks corresponding to ? (110) were detected in vacuum SLM processed samples.
9738-12, Session 7
Alberto Piqué, Iyoel Beniam, Scott A Mathews, Nicholas A .
Charipar, U .S . Naval Research Lab . (United States)
The use of laser-induced forward transfer (LIFT) techniques for the printing of functional materials has been demonstrated for numerous applications.
Traditionally, the printing results in 2D patterns being generated nonlithographically, while more recently various groups have demonstrated electrical interconnects from laser printed 3D structures. The laser printing of these interconnects takes place through aggregation of voxels of either molten metal or of dispersed metallic nanoparticles. However, the generated
3D structures do not posses the same metallic conductivity as a bulk metal interconnect of the same cross-section and length as those formed by wire bonding or tab welding. It is possible, however, to laser transfer entire structures using a technique developed at NRL known as lase-and-place.
Lase-and-place is a LIFT process whereby whole components and parts can be transferred from a donor substrate onto a desired location with one single laser pulse. This paper will describe the use of LIFT to laser print freestanding, solid metal interconnects precisely over devices contact pads to make functional circuits. Furthermore, this paper will also show how the same laser can be used to bend or fold the bulk metal foils prior to transfer, thus forming compliant 3D structures able to provide strain relief for flexible circuits or thermal mismatch. These interconnect “bridges” can span wide gaps (on the order of several hundred microns) and accommodate height differences of tens of micron between adjacent devices. Examples of these laser printed 3D metallic bridges and their role in the development of next generation electronics by additive manufacturing will be presented.
This work was funded by the Office of Naval Research (ONR) through the
Naval Research Laboratory Basic Research Program.
9738-11, Session 7
(Invited Paper)
Ioanna Zergioti, National Technical Univ . of Athens
(Greece)
This paper reviews the latest developments and the background of Laser
Induced Forward Transfer as a 3D manufacturing approach for functional devices with applications in organic electronics and in biotechnology.
Current technological trends require the precise deposition of highly resolved features, in a direct writing approach which preserve their structural and electronic properties upon transfer, while increasing the number of components that can be integrated in a single device. Laser
Induced Forward Transfer meets these requirements. Examples of selected applications, including organic thin-film transistors, metallic interconnects, circuits defects repairing, chemical sensors and biosensors will be presented, highlighting the potential incorporation of lasers into the direct printing of entire devices and components. In particular, the successful laser printing of polymers, metals, semiconducting inks, 2D nanomaterials, and viable biological materials such as DNA, proteins and enzymes with high spatial resolution offers unique advantages as compared to traditional inkjet and thin film techniques. Moreover, the mechanisms of liquid and solid phase LIFT through time-resolved studies will be discussed, while post printing processes such as laser sintering will also be addressed.
9738-13, Session 7
David Munoz-Martin, Univ . Politécnica de Madrid (Spain);
C . Frederik Brasz, Princeton Univ . (United States); Chen
Yu, Miguel Morales, Univ . Politécnica de Madrid (Spain);
Craig B . Arnold, Princeton Univ . (United States); Carlos
Molpeceres, Univ . Politécnica de Madrid (Spain)
Laser induced forward transfer (LIFT) technique can be used for printing metallic contacts onto flexible optoelectronics devices in flex/3D electronics industry, patterning solder paste for microelectronics or for the metallization of the front side of solar cells. In the latter case, one of the aims of solar cell researchers and manufacturers is to find technologies leading to an increase in the efficiencies of solar cells while keeping costs low. Specifically, procedures capable of making better contacts by improving the aspect ratio and decreasing contact losses are sough.
In this work, a study of LIFT of single dots of a high viscosity silver paste, designed for screen-printing of solar cells, was performed using a ns-pulsed laser at 532 nm. Phenomenological and analytical descriptions are given of the influence of process parameters on the morphology of transferred paste dots characterized by means of confocal microscopy. Time-resolved imaging was implemented in another LIFT dotting experiment with similar experimental conditions in order to illuminate the transfer dynamics in relation to the pulse energy and paste thickness. Four transfer regimes are defined in accordance with the observed distinctive paste dot morphologies on the acceptor: non-dot transfer, in which the pulse energy is below the transfer threshold of a given paste thickness; cluster-dot transfer, where the dot size increases as a function of pulse energy for relatively thin films of paste; concrete-dot transfer, when the paste is thick enough to allow the protruding jet to impact the acceptor substrate without separating from the donor substrate; and explosion-dot transfer, where the high laser pulse energy generates a bursting ejection on the donor that splashes paste on the acceptor.
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Conference 9738: Laser 3D Manufacturing III
9738-14, Session 8
(Invited Paper)
Lorenzo Valdevit, Univ . of California, Irvine (United States)
Reducing mass without sacrificing mechanical integrity and performance is a critical goal in a vast range of applications. Introducing a controlled amount of porosity in a strong and dense material (hence fabricating a cellular solid) is an obvious avenue to weight reduction. The mechanical effectiveness of this strategy, though, depends strongly on the architecture of the resulting cellular material (i.e., the topology of the introduced porosity). Recent progress in additive manufacturing enables fabrication of macro-scale cellular materials (both single-phase and hybrid) with unprecedented dimensional control on the unit-cell and sub-unit-cell features, potentially producing architectures with structural hierarchy from the nano to the macro-scale. As mechanical properties of materials often exhibit beneficial size effects at the nanoscale (e.g., strengthening of metals and toughening of ceramics), these novel manufacturing approaches provide a unique opportunity to translate these beneficial effects to the macroscale, further improving the mechanical performance of architected materials.
In this presentation, I will review a number of advanced manufacturing technologies that allow fabrication of 3D architected materials with high structural hierarchy, and provide recent examples of micro and nanoarchitected materials with superior combinations of properties. The urgent need to form strong synergies among the fields of additive manufacturing, topology optimization and architecture-properties relations will be emphasized throughout.
9738-15, Session 8
(Invited Paper)
Corentin Coulais, Leiden Univ . (Netherlands)
Mechanical metamaterials exhibit a wide range of unusual properties, including negative response, cloaking, topological insulation and programmability. Such materials consist of periodic stackings of unit cells, where the unit cell design encodes the materials functionality.
This periodicity limits their potential, as these metamaterials exhibit a homogeneous response. Here we introduce a combinatorial strategy to create a vast number of distinct, three-dimensional mechanical metamaterials. These materials consist of aperiodic stackings of anisotropic unit cells, and their functionality results from both the unit cell and the stacking order. We create such metamaterials by 3D printing, and experimentally demonstrate that the information embedded in the stacking order spawns completely novel properties.
First, their surfaces can morph into an arbitrary texture. Second, their mechanics is sensitive to the pattern of the surface they are in contact with.
Our combinatorial approach opens pathways for the design of functional structures programmed with specific mechanical tasks, which blur the boundary between material and machine.
9738-16, Session 8
Sergey Mekhontsev, Weston L . Tew, Steven E . Grantham,
Vladimir B . Khromchenko, Leonard M . Hanssen, National
Institute of Standards and Technology (United States)
Knowledge of the optical properties of materials such as spectral emittance and reflectance is essential for non-contact thermometry, heat transfer modeling, and prediction of directed energy source coupling with targets
(for example, in laser-based material processing and manufacturing).
Even the common “emissivity-free” multi-spectral methods of radiation thermometry, which do require absolute knowledge of emittance, can greatly benefit from validation using well-characterized materials of interest along with accurate absolute temperature measurements of the surface.
TEMPS (Temperature and Emittance of Melts, Powders and Solids) is a new facility under construction at NIST, which is designed for the accurate measurement of material emittance, reflectance and true surface temperature and is aimed at the establishment of measurement traceability and best practices for non-contact thermometry in additive manufacturing.
This will enable improvements in the reproducibility and control of manufacturing processes. This paper describes the objectives, goals, and development status of this facility.
9738-17, Session 8
(Invited Paper)
Owen Hildreth, Arizona State Univ . (United States);
Timothy W . Simpson, The Pennsylvania State Univ . (United
States)
Advances in metallic 3D printing combined with renewed interests in additive manufacturing have opened up a host of new technologies and ideas for both the applications of lasers and the exploration of new material systems. Newer multi-metal powder-flow laser melt/sintering printers is one of the key technologies that enable scientists to study complex metallic systems in a rapid manner. While publications detail the mechanical and physical properties of multi-metal, heterogeneous printed structures, there has been very little reported on the electrochemical and corrosion stability of these new material structures. This paper details the electrochemical and corrosion properties of metallic structures printed using multi-metal powder-flow laser sintering techniques. Particular attention is given to how both printing process and post-printing heat treatments impact the electrochemical and corrosion behaviors of the metal/metal interface.
9738-18, Session 8
(Invited Paper)
Baolong Zheng, Yizhang Zhou, Univ . of California, Irvine
(United States); Nancy Y . C . Yang, Sandia National Labs .
(United States); Enrique J . Lavernia, Julie M . Schoenung,
Univ . of California, Irvine (United States)
Additive manufacturing (AM) has evolved from rapid prototyping to 3D printing manufacturing that can create parts directly from CAD solid models without the use of tooling. Among various AM processing, laser engineered net shaping (LENS) is one of the fastest growing laser powder injection deposition processes. In this report, recent research and progress associated with development of alloys and composites using LENS are reviewed, such as Fe- and Ti-based alloys, Ti+TiC and Ni+TiC composites,
Al+Al3Ni composite foam, and WC+Co cermets. In addition to fabricating complex geometries of dense metals and composites, the microstructure can be tailored by controlling both composition and process parameters.
For processing improvement, the closed-loop diagnostics and controls with in-situ molten pool sensor and Z-height control subsystems are being developed, while the thermal behavior measurement with thermal imaging and thermocouple methods, and numerical simulation are also being extensively investigated. The trends and challenges associated with direct laser fabrication of novel materials, as well as existing problems with residual stress and porosity in deposited materials are also discussed.
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Conference 9738: Laser 3D Manufacturing III
9738-19, Session 9
(Invited Paper)
Wayne King, Lawrence Livermore National Lab . (United
States)
The metal laser powder bed fusion additive manufacturing process uses high power lasers to build parts layer upon layer by melting fine metal powders. Certification of parts produced using this technology is broadly recognized as a significant challenge. There are two elements that have been identified as being foundational to certification of additively manufactured metal parte: (1) physics-based process models and (2) inline process monitoring and control. In this presentation, we discuss a multiscale
(length and time) modeling strategy that will serve as the foundation upon which process control and part certification can be built. These include a model at the scale of the powder that addresses the question, “Can a metal powder be processed by additive manufacturing and what are the optimal processing conditions?”, simulates single track/single-multi layer builds, and provides powder bed and melt pool thermal data. A second model computationally builds a complete part and predicts manufactured properties (residual stress, density, dimensional accuracy) in 3D. Modeling is tied to experiment through real-time in line process monitoring using a high-speed infrared camera that images the melt pool. In this presentation, we focus on how the metal powders are modeled including the interaction of the laser with the powder layer and the effects of powder size distribution
9738-21, Session 9
(Invited Paper)
Edward W . Reutzel, Abdalla R . Nassar, John P . Morgan
Jr ., Donald J . Natale, Sean D . Knecht, Richard L . Tutwiler,
Applied Research Lab . (United States)
Additive manufacturing of metal components through directed energy deposition or powder bed fusion is a complex undertaking, often involving hundreds or thousands of individual laser deposits. During processing, conditions may fluctuate, e.g. material feed rate, beam power, surrounding gas composition, local and global temperature, build geometry, etc., leading to unintended variations in final part geometry, microstructure and properties. To assess or control as-deposited quality, researchers have used a variety of methods, including those based on sensing of melt pool and plume emission characteristics, characteristics of powder application, and layerwise imaging.
Here, a summary of ongoing process monitoring activities at Penn State is provided, along with a discussion of recent advancements in the area of layerwise image acquisition and analysis during powder bed fusion processing. Specifically, methods that enable direct comparisons of CAD model, build images, and 3D microtomographic scan data will be covered, along with thoughts on how such analyses can be related to overall process quality.
9738-20, Session 9
Guangying Guan, The Univ . of Nottingham (United
Kingdom); Zeng H . Lu, The Univ . of Sheffield (United
Kingdom); Matthias Hirsch, Ruth Goodridge, The Univ . of
Nottingham (United Kingdom); David T . D . Childs, Stephen
J . Matcher, The Univ . of Sheffield (United Kingdom); Adam
T . Clare, The Univ . of Nottingham (United Kingdom);
Kristian M . Groom, The Univ . of Sheffield (United Kingdom)
Selective laser sintering (SLS) enables the fast, flexible and cost-efficient production of polymer parts directly from 3D CAD. However, there is a marked lack of process monitoring and feedback control of key process variables in SLS, preventing its wider uptake in high-value or safety critical applications. In this study, optical coherence tomography (OCT) is used for the first time to evaluate components produced by SLS. Surface defects in Polyamide parts are analyzed ex-situ and the limiting factors associated with the measurement technique are quantified. OCT is compared with
X-ray computed tomography (XCT) and is shown to be a powerful technique for evaluating surface irregularities and sub-surface defects that have resulted from poor sintering or non-homogeneous powder spreading.
We demonstrate detection and quantification of surface defects such as cracks, pores and voids on a ~30 µ m scale, using a commercial 1300nm OCT system. Furthermore, we show that this technique can resolve fine features incorporated within a 200 to 400 µ m depth below the surface, covering typical layer thicknesses used in SLS. Sub-surface features typical of those observed in SLS, such as voids, contaminants and regions of controlled porosity, are built into the part and are both examined and compared with the process parameters. This capability paves the way for real-time monitoring of the SLS process for assurance, or even dynamic correction of defects during part manufacture, and will also save time and material wasted in poorly sintered parts.
9738-22, Session 9
Steven E . Grantham, Brandon Lane, Jorge E . Neira, Sergey
Mekhontsev, Mihaela Vlasea, Leonard M . Hanssen, National
Institute of Standards and Technology (United States)
NIST’s Physical Measurement and Engineering Laboratories are jointly developing the Additive Manufacturing Measurement Testbed (AMMT)/
Temperature and Emittance of Melts, Powders and Solids (TEMPS) facilities.
These facilities will be co-located on an open architecture laser-based powder bed fusion system allowing users full access to the system’s operation parameters. This will provide users with access to machineindependent monitoring and control of the powder bed fusion process.
In this paper there will be emphasis the AMMT which incorporates in-line visible light collection optics for monitoring and feedback control of the powder bed fusion process. We shall present an overview of the AMMT/
TEMPs program and it goals. The optical and mechanical design of the open architecture powder-bed fusion system and the AMMT will be also be described. In addition, preliminary measurement results from the system along with the current system status of and future plans the will be discussed.
9738-23, Session 9
(Invited Paper)
Giacomo Cerretti, Daniele Martella, Hao Zeng, Camilla
Parmeggiani, European Lab . for Non-linear Spectroscopy
(Italy); Stefano Palagi, Max Planck Institute for Intelligent
Systems (Germany); Andrew G . Mark, Max-Planck-
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Conference 9738: Laser 3D Manufacturing III
Gesellschaft (Germany); Kai Melde, Max Planck Institute for Intelligent Systems (Germany); Tian Qiu, Max-Planck-
Institut für Intelligente Systeme (Germany); Peer Fischer,
Max Planck Institute for Intelligent Systems (Germany);
Diederik S . Wiersma, European Lab . for Non-linear
Spectroscopy (Italy)
The talk will cover very recent, even newer results which were just submitted to Nature Communications.
silicon with the help of USP’s. In this context we investigated the influence of pulse energy, repetition rate and scanning velocity with respect to the formed melting.
The experiments were performed using 500fs pulses at a wavelength of
1030nm setting the laser fluence close to the ablation threshold of the powder grains to ensure high energy deposition and avoid a transition to the gaseous phase. The influence of the temporal pulse-to-pulse separation was studied in detail in order to evaluate heat accumulation effects. We could successfully demonstrate the local melting of the powder with successive single pulses. Heat accumulation can be used to control the thermally influenced zone. The extremely high cooling rates could help to improve mechanical and thermal properties of the microstructure and offer new possibilities in the processing of light-weight elements for manifold applications in aerospace and automotive.
9738-24, Session 10
(Invited Paper)
Jian Liu, Pei Yang, Baolong Zheng, Huan Huang, Shuang
Bai, PolarOnyx, Inc . (United States); Lih-Mei Yang,
PolarOnyx Laser Inc . (United States)
The current development focus of additive manufacturing (AM) is to produce complex shaped functional metallic components, including metals and alloys, to meet demanding requirements from different industries such as aerospace, defense and biomedicines. So far, one of the major problems has been the standardization of the optimal parameters. The setting of the appropriate processing conditions can lead to the acquisition of the desired characteristics in terms of morphology, porosity, hardness, microstructural and mechanical properties of the processed components.
In this paper, additive manufacturing of Tungsten materials is investigated to study the optimal parameters space that allows the formation of a continuous layer of material by using femtosecond fiber lasers. Mechanical properties (strength and hardness) and micro-structures (grain size) of the fabricated parts are investigated to establish a relationship between material, process, and metallurgical mechanism of Tungsten components.
Literature data on the CW laser process will be used as benchmark for comparison with the fs laser, in which microstructures significantly deviating from the equilibrium were obtained. Fully dense Tungsten part with refined grain and increased hardness was obtained compared with others with CW laser. The results show evidence that the fs laser based AM could promote improved mechanical properties due to controlled heat input, extreme high temperature and the more rapid cooling rates achieved compared with a CW or long pulsed laser. This can greatly benefit the applications in automobile, aerospace and biomedical industries.
9738-26, Session 10
David B . Witkin, Henry Helvajian, Lee F . Steffeney, William
W . Hansen, The Aerospace Corp . (United States)
The effect of laser remelting of surfaces of as-built Selective Laser Melted
(SLM) Inconel 625 was evaluated for its potential to improve the surface roughness of SLM parts. Alloys made by SLM have properties similar to their wrought counterparts, but surface roughness of SLM-made parts is much higher than found in standard machining operations. This has implications for mechanical properties of SLM materials, such as a large debit in fatigue properties, and in applications of SLM, where surface roughness can alter fluid flow characteristics. Because complexity and net-shape fabrication are fundamental advantages of Additive Manufacturing (AM), post-processing by mechanical means to reduce surface roughness detracts from the potential utility of AM. Use of a laser to improve surface roughness by targeted remelting or annealing offers the possibility of in-situ surface polishing of AM surfaces- the same laser used to melt the powder could be amplitude modulated to smooth the part during the build. The effects of remelting the surfaces of SLM Inconel 625 were demonstrated using a CW fiber laser (IPG: 1064 nm, 2-50 W) that is amplitude modulated with a pulse profile to induce remelting without spallation or ablation. The results show that with an appropriate pulse profile that meters the heat-load, surface features such as partially sintered powder particles and surface connected porosity can be mitigated via a secondary remelting/annealing event.
Techniques are also under development that can measure surface roughness during a build and thereby enable the application of a “corrective” remelting/annealing pulse if necessary.
9738-25, Session 10
Tobias Ullsperger, Gabor Matthäus, Markus Rettenmayr,
Friedrich-Schiller-Univ . Jena (Germany); Stefan
Risse, Fraunhofer-Institut für Angewandte Optik und
Feinmechanik (Germany); Andreas Tünnermann,
Stefan Nolte, Friedrich-Schiller-Univ . Jena (Germany) and Fraunhofer-Institut für Angewandte Optik und
Feinmechanik (Germany)
Direct Metal laser sintering (DMLS) is an outstanding additive technique that enables a powder based stepwise fabrication of nearly every complex three-dimensional shape. Typically, cw or long pulse lasers are used, while the utilization of ultrashort laser pulses (USP) has been barely investigated yet. The advantages of short pulses in interaction with matter are especially the reduction of the heat affected zone and the vast cooling rate which is not achievable with conventional methods. To this end we demonstrate the feasibility of melting micro powder that consists of aluminum alloyed with
9738-27, Session 10
Hu Zhang, Haihong Zhu, Xiaojia Nie, Ting Qi, Zhiheng Hu,
Xiaoyan Zeng, Huazhong Univ . of Science and Technology
(China)
The proposed paper illustrates fabrication and heat treatment of high strength Al-Cu-Mg alloy produced by selective laser melting (SLM) process.
Al-Cu-Mg alloy is one of the heat treatable aluminum alloys regarded as difficult to fusion weld. SLM is an additive manufacturing technique through which components are built by selectively melting powder layers with a focused laser beam. The process is characterized by short laser-powder interaction times and localized high heat input, which leads to steep thermal gradients, rapid solidification and fast cooling. In this research, 3D Al-Cu-
Mg parts with relative high density of 99.8% are produced by SLM from gas atomized powders. Room temperature tensile tests reveal a remarkable
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Conference 9738: Laser 3D Manufacturing III mechanical behavior: the samples show yield and tensile strengths of about
276 MPa and 402 MPa, respectively, along with fracture strain of 6%. The effect of solution treatment and aging treatment on microstructure and related tensile properties is examined and the results demonstrate that the mechanical behavior of the SLMed Al-Cu-Mg samples can be tuned within a wide range of strength and ductility through proper heat treatment. using a customized genetic algorithm developed for optimizing cellular scanning strategy for selective laser melting, with an objective of reducing residual stresses and deformations. The resulting thermo-mechanically optimized cellular scanning strategies are compared with standard scanning strategies and thermally-optimized scanning strategies which have been used to manufacture standard samples.
9738-28, Session 11
(Invited Paper)
Junjie Luo, Luke Gilbert, Douglas A . Bristow, Robert G .
Landers, Missouri Univ . of Science and Technology (United
States); Jonathan T . Goldstein, Augustine M . Urbas, Air
Force Research Lab . (United States); Edward C . Kinzel,
Missouri Univ . of Science and Technology (United States)
Additive manufacturing is becoming increasingly accepted for printing plastics, metals, and some ceramics. However, comparatively little work has been performed on printing glass and other optical components aside from polymers. Ongoing work on depositing transparent glass components will be presented including printing soda-lime, fused quartz, and optical fiber. While multiple additive manufacturing techniques can deposit glass, including powder-bed and blown-powder processes, feeding a filament directly into the melt-pool minimizes entrapping bubbles during deposition.
This presentation will focus on filament-fed results. In this process a CO2 laser is used to locally heat and melt the glass. The build platform is scanned by moving a heated build platform under a stationary laser beam. Material is consolidated by the melting process, solidifies as the part translates relative to the laser beam. The key parameters for each process are identified, notably the scan speed, laser power, and feed-rates. These are mapped in terms of their effects on the morphology and optical properties of the printed glass. The relationship between these parameters is studied experimentally and corroborated with numerical simulations (ANSYS Fluent) of the melt pool temperature. We use the optimized parameters to build parts including simple convex glass lenses. The free surface of the printed part can be very smooth because the laser effectively flame polishes the part. In-situ spectrometry is used to monitor the process. The additive manufacturing process allows the material composition to be adjusted locally on a 3D volumetric basis for making gradient index optics.
9738-30, Session 11
Henry Helvajian, Anthony J . Manzo, Shant Kenderian, The
Aerospace Corp . (United States)
The change in properties of a propagating ultrasonic wave has been a mainstay characterization tool of the nondestructive evaluation (NDE) industry for identifying subsurface defects (e.g. damage). A variant of this concept could be applicable to 3D additive manufacturing where the existence of defects (e.g. pores) within a sublayer could mark a product as non-qualifying. We have been exploring the utility of pulsed laser ultrasonic excitation coupled with CW laser heterodyne detection as an all optical scheme for characterizing sub surface layer properties. The all-optical approach permits a straight forward integration into a laser additive processing tool. To test the concept, we have developed an experimental system that generates pulsed ultrasonic waves (the probe) with high bandwidth (>> 10MHz) and a surface displacement sensor that can capture the ultrasonic signal “return” with bandwidth close to 300 MHz.
The use of high frequencies enables the detection of smaller defect sites.
The technique is time resolved with the sensor and probe as point (~ 10-30 microns) beams. Current tests include characterizing properties of weld joints between two thin stainless steel plates. The long term objective is to transition the technique into a laser additive manufacturing tool.
9738-29, Session 11
Sankhya Mohanty, Jesper H . Hattel, Technical Univ . of
Denmark (Denmark)
Residual stresses and deformations continue to remain one of the primary challenges towards expanding the scope of selective laser melting as an industrial scale manufacturing process. While process monitoring and feedback-based process control of the process has shown significant potential, there is still dearth of techniques to tackle the issue. Numerical modelling of selective laser melting process has thus been an active area of research in the last few years. However, large computational resource requirements have slowed the usage of these models for optimizing the process.
In this paper, a calibrated, fast, multiscale thermal model coupled with a 3D finite element mechanical model is used to simulate residual stress formation and deformations during selective laser melting. The resulting reduction in computation time allows evolutionary algorithm-based optimization of the process. A multilevel optimization strategy is adopted
9738-31, Session 11
(Invited Paper)
Jason B . Jones, Hybrid Manufacturing Technologies
(United States)
The advent of laser technology has been a key enabler for industrial 3D printing, know as Additive Manufacturing (AM). Despite its commercial success and unique technical capabilities, laser-based AM systems are not yet able to produce parts with the same accuracy and surface finish as CNC machining. To enable the geometry and material freedoms afforded by
AM, yet achieve the precision and productivity of CNC machining, hybrid combinations of these two processes have started to gain traction.
To achieve the benefits of combined processing, laser technology has been integrated into mainstream CNC machines - effectively repurposing them as hybrid manufacturing platforms. This presentation reviews how this engineering challenge has prompted beam delivery innovations to allow automated changeover between laser processing and machining, using standard CNC tool changers. Handling laser-processing heads using the tool changer also enables automated change over between different types of laser processing heads, further expanding the breadth of laser processing flexibility in a hybrid CNC. This presentation highlights the development, challenges and future impact of hybrid CNCs on laser processing.
168 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9738: Laser 3D Manufacturing III
9738-32, Session 12
(Invited Paper)
Robert A . Norwood, Khanh Q . Kieu, Gregory A . Cohoon,
College of Optical Sciences, The Univ . of Arizona (United
States); Babak Amirsolaimani, Soha Namnabat, Jeff Pyun,
The Univ . of Arizona (United States)
The advent of advanced solid-state lasers, specifically fiber lasers, has ushered in a new era in laser writing. At the same time, multiphoton
3D writing has continued to develop, with new materials with higher contrast and associated secondary properties increasingly available. While modelocked Ti:sapphire lasers have been the workhorse for multiphoton writing systems, the recent development of compact, femtosecond fiber lasers enable turn-key multiphoton lithography systems to be a reality, and provide a route to the creation of sophisticated photonic structures, such as 3D microresonators and integrated nanophotonic circuitry. We present several developments regarding the use of femtosecond lasers for the creation of sophisticated micro- and nanophotonic device structures.
We first present the use of a Ti:sapphire laser for the ablative creation of microresonator disks with high quality factors (Q) in optical fiber; the ultra-low loss of optical fiber coupled with simple post-processing result in resonators with Q’s approaching ten million. We then discuss the development of modelocked femtosecond fiber laser-based systems for nanophotonic circuit writing, primarily in a three-photon modality. The modelocked fiber laser at the heart of this system is hand-held and relies on a novel tapered fiber-based carbon nanotube saturable absorber for modelocking, and the three-photon modality increases the options for resist materials significantly, compared to the two-photon case, owing to parity spectroscopic selection rules. Finally we discuss associated writable optical polymer material advances, some of which have potential for applications in the mid-infrared.
9738-34, Session 12
(Invited Paper)
Peter M . Grubb, The Univ . of Texas at Austin (United
States); Harish Subbaraman, Omega Optics, Inc . (United
States); Ray T . Chen, The Univ . of Texas at Austin (United
States)
A complete inkjet-printed 3D structure containing 50 Ohm transmission lines, CNT-based FET, switching network and phased array antenna pads are printed in a conformable substrate. Large steering angles and high frequency switching speed of the CNT-based FET are demonstrated which can be used for air-borne and space-borne applications for remote sensing and free space wireless communications.
9738-35, Session 12
Zuleykhan Tomova, John T . Fourkas, Univ . of Maryland,
College Park (United States)
Novel visible-light-based lithographic techniques have demonstrated high potential in achieving the super resolution of the fabricated features.
Nonlinear interaction of light from even a single visible laser beam can lead to the formation of the isolated structures with size of 100 nm or smaller. Different exposure schemes, involving a second light source, allow for control of the chemical polymerization reaction. In such approaches, nonlinear absorption from a first laser beam excites molecules to a higher energy state that can produce free radicals and initiate a polymerization reaction. Simultaneous exposure to a second laser beam, typically in continuous wave mode, can prevent polymerization through deactivating molecules from the excited state back to the ground state before they can form free radicals. It is further possible to limit size of the structures by spatially changing the profile of the laser beam to only deactivate excited molecules in selected regions. Even though such two-color lithography has been demonstrated to have the ability to fabricate small isolated features, the two competing chemical processes, deactivation and free-radical formation, that are initiated form the excited state limit its potential for applications that require fabrication of close-packed features. This problem can be avoided by employing a three-color lithography scheme, in which the state that produces free radicals, differ from a state that deactivates molecules. In this work, we have explored various exposure schemes to achieve smallest pitch and spacewidth distance down to 60 nm.
9738-36, Session 12
(Invited Paper)
John Tumbleston, Carbon3D, Inc . (United States)
Continuous liquid interface production (CLIP) can rapidly produce 3D parts using a range of polymeric materials. A DLP-based technique, CLIP proceeds via projecting a sequence of UV images through an oxygenpermeable, UV-transparent window below a liquid resin bath. A thin uncured liquid layer, or dead zone, is created above the window and maintains a liquid interface below the advancing part. Above the dead zone, the curing part is drawn out of the resin bath creating suction forces that renew reactive liquid resin. The dead zone is created due to oxygen inhibition of photopolymerization, a process that is traditionally a nuisance in other photopolymerization applications. However, for CLIP oxygen inhibition and creation of the dead zone allows for a continuous mode of printing where UV exposure, resin renewal, and part elevation are conducted simultaneously. This continual process is fundamentally different from traditional bottom-up stereolithography printers where these steps must be conducted in separate and discrete steps. Furthermore, the relatively gentle nature of CLIP due to the established dead zone enables the use of unique materials with a wide range of mechanical properties. This presentation will showcase the CLIP technology and provide a detailed picture of interactions between different resin and process parameters. New applications for 3D printing that span the micro- to macro-scale enabled by CLIP’s combination of unique materials and part production speed will also be presented.
9738-37, Session 12
(Invited Paper)
Jimin Chen, Beijing Univ . of Technology (China)
The surgary doctor makes use of the guide to helps them to operate with
3D printing technology . These printed guide make the operation easy and time saving while operation. In this paper we intruduced an application of
3D printing technology in tumor operation.Currently for tumor treatment main methods are surgery, radiotherapy, chemotherapy. Howeve.traditional radioactive rays kill cancer cells as well as normal tissues. A radioactive seed implantation treatment technology has been introduced to treat tumor. It implants the tiny radioactive seeds into tumor and kill cancer cells only.The problem is to position the seeds in tumor exactly. Traditionally the digital laminography was used frequently during invasive procedure.It is expensive and cost time. We use 3D printing to print guide for this operation.Method puncture needle - localization guided by printed guide was performed in face tumors and prepared for operation. It is concluded that the new type guide is dominantly advantageous.
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9739-1, Session 1
Daniel Troendle, Patricia Martin Pimentel, Christoph
Rochow, Herwig Zech, Gerd Muehlnikel, Frank F . Heine,
Tesat-Spacecom GmbH & Co . KG (Germany); Rolf Meyer,
Sabine D . Philipp-May, Michael Lutzer, Deutsches Zentrum für Luft- und Raumfahrt e .V . (Germany); Edoardo Benzi,
Philippe Sivac, Silvia Mezzasoma, Harald Hauschildt, Mike
Krassenburg, European Space Research and Technology
Ctr . (Netherlands); Ian Shurmer, European Space Research and Technology Ctr . (Germany)
Laser Communication Links in Orbit have become routine for Alphasat TDP1
GEO data relay and the Sentinel-1A LEO satellite. The Laser Communication
Terminals (LCTs) onboard both satellites provide optical LEO-GEO communication links at data rates up to 1.8 Gbps, with a design that could scale up to 7.2 Gbps in the future.
In November 2014, the first optical link between both satellites was established. Since then, a large number of links have been performed with both quasi-operational and experimental character. The campaign has demonstrated stable and bit-error free links over LEO-GEO distances of up to 45’000km with optical transmit power of only 1.1W. With a system requirement of BER<10-8 at 2W optical transmit power and up to 5W available, this verifies the excellent system budgets and margins for LEO-
GEO and GEO-GEO links. The existing design is capable to cover GEO to GEO links of 72’000km at 1.8Gbps data rate. The margin offers the possibility to simplify future LEO terminals or to increase the data rate. The link acquisition, consisting of spatial acquisition and frequency acquisition, is achieved reliably within less than the originally specified 55s. Links with low grazing altitude investigate the impact of atmosphere to link performance.
The paper will provide details of in-orbit system performance.
The optical inter-satellite links between Sentinel-1A and Alphasat are in collaboration of ESA, German Aerospace Center DLR, and TESAT
Spacecom, Germany. LCTs and RF downlink system have been developed by TESAT Spacecom with funding from DLR and ESA. Launched in 2013, the geostationary Alphasat, Europe’s largest telecommunications satellite, is a
Public Private Partnership between ESA and UK satellite operator, Inmarsat.
Sentinel-1A is a European radar imaging satellite launched in 2014 as part of the EU Copernicus programme. Sentinel-2A, a European multi-spectral imaging satellite under the EU Copernicus programme, was launched in
June 2015 and also carries an LCT. Link commissioning with Alphasat is foreseen during second half of 2015.
Alphasat TDP1 serves as the precursor for the forthcoming European Data
Relay Satellite System (EDRS). EDRS will eventually consist of a network of dedicated geostationary satellites providing data relay services. The first,
EDRS-A, is planned to be launched by end 2015 and will start its service beginning 2016.
9739-2, Session 1
(Invited Paper)
Hideki Takenaka, Yoshisada Koyama, Maki Akioka,
Dimitar Kolev, Naohiko Iwakiri, National Institute of
Information and Communications Technology (Japan);
Hiroo Kunimori, Alberto Carrasco-Casado, NICT (Japan);
Yasushi Munemasa, National Institute of Information and Communications Technology (Japan); Eiji Okamoto,
Nagoya Institute of Technology (Japan); Morio Toyoshima,
National Institute of Information and Communications
Technology (Japan)
Research and development of space optical communications is conducted in National Institute of Information and Communications Technology (NICT), and the practical use of space optical communications is explored. NICT developed Small Optical TrAnsponder (SOTA), which was embarked on a
50kg-class satellite and launched into a low earth orbit (LEO). Atmospheric turbulence causes signal fadings and becomes an issue to be solved in satellite-to-ground laser communication links. Therefore, as error correcting functions, a Reed-Solomon (RS) code and a Low-Density Generator Matrix
(LDGM) code are implemented in the communication system onboard SOTA.
In this paper, we present the communication performance with the LDGM code via satellite-to-ground atmospheric paths including the link budget analysis and the comparison between theoretical and experimental results.
9739-3, Session 1
(Invited Paper)
Malcolm W . Wright, Joseph M . Kovalik, Jet Propulsion
Lab . (United States); Jeff Morris, The Boeing Co . (United
States); Matthew Abrahamson, Abhijit Biswas, Jet
Propulsion Lab . (United States)
The Optical PAyload for Lasercomm Science (OPALS) experiment on the International Space Station (ISS) recently demonstrated successful optical downlinks to the NASA/JPL 1-m aperture telescope at the Optical
Communication Telescope Laboratory (OCTL) located near Wrightwood, CA.
A large area (200 um diameter) free space coupled avalanche photodiode
(APD) detector was used to receive video and a bit patterns at 50 Mb/s.
We report on a recent experiment that used an adaptive optics system at
OCTL to correct for atmospherically-induced refractive index fluctuations so that the downlink from the ISS could be coupled into a single mode fiber receiver. Stable fiber coupled power was achieved over an entire pass using a self-referencing interferometer based adaptive optics system that was provided and operated by Boeing Co. and integrated to OCTL.
End-to-end transmission and reconstruction of an HD video signal verified the communication performance as in the original OPALS demonstration.
Coupling the signal into a single mode fiber opens the possibility for higher bandwidth and efficiency modulation schemes and serves as a pilot experiment for future implementations.
170 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII
9739-4, Session 1
Ryan W . Kingsbury, Massachusetts Institute of Technology
(United States); David O . Caplan, MIT Lincoln Lab .
(United States); Kerri L . Cahoy, Massachusetts Institute of
Technology (United States) obtaining diffraction limited receiver performance, necessary for BPSK (as used in the TESAT LCT) and DPSK based laser communication systems.
Currently the TAOGS is co-located with the European Space Agency (ESA)
Optical Ground Station on Tenerife. The up- and downlink performance of the station to the Alphasat LCT is tested in several experimental campaigns; the results are given in the paper.
*Alphasat – Sentinel-1A Optical Inter-Satellite Links:RUN-UP for the
European Data Relay Satellite System, this conference
**Satellite Quantum Communication via the Alphasat Laser Communication
Terminal, ICSOS 2015
In this paper, we present the implementation and validation of a MOPAbased laser transmitter suitable for use within resource-constrained
CubeSats. A fully COTS-based approach was taken to achieve a design that is compatible with CubeSat cost and lead time constraints. The transmitter produces a high-fidelity, 200 mW average power optical output at 1550 nm with less than 8 W electrical input power.
The transmitter design consists of an FPGA-based modulator directly modulating a compact seed laser / TEC module with a pulse position modulation (PPM) waveform. The modulation-induced chirp of the seed laser optical output is used in conjunction with a narrow fiber Bragg grating filter, which performs FM-to-AM conversion that improves the modulation extinction ratio (ER) to greater than 40 dB. The low duty cycle (PPM-
8 through PPM-128) signal is subsequently amplified by a COTS-based
Erbium-doped Fiber Amplifier (EDFA) to achieve peak transmit powers approaching 25 W.
The transmitter also incorporates a variety of built-in self-test (BIST) features that facilitate incremental testing and calibration both in the lab and on orbit. Implementation of the BIST functions have minimal impact on size, weight, and power since it only requires an additional coupler, photodiode, and comparator, and leveraging spare logic resources available in the FPGA. This enables in-situ measurement of important transmitter performance metrics such as peak power and ER. BIST can also operate as a loopback receiver to validate sensitivity of the communications detector, and using this capability, net transmitter-to-receiver communication performance was measured within 3 dB from theory.
9739-5, Session 2
Karen Saucke, Frank F . Heine, Mark Gregory, Daniel
Troendle, Christoph Seiter, Tesat-Spacecom GmbH & Co .
KG (Germany); Edgar Fischer, Thomas Berkefeld, Mikael
Feriencik, Marco Feriencik, Synopta GmbH (Switzerland);
Ines Richter, Rolf Meyer, Deutsches Zentrum für Luft- und
Raumfahrt e .V . (Germany)
9739-6, Session 2
Todd S . Rose, Richard P . Welle, Darren W . Rowen, Siegfried
W . Janson, Stephen D . LaLumondiere, Nicolette I . Werner,
The Aerospace Corp . (United States)
We report on CubeSat space-to-ground optical communication links funded by NASA’s Optical Communication and Sensor Demonstration program.
The links use beam divergences compatible with current CubeSat pointing capabilities. The first of three 1.5 U spacecraft implements a 5-W fiber laser with a modest 0.35-degree divergent beam and is configured to transmit data up to 200 Mb/s. This vehicle has been delivered and scheduled for launch in early fall of 2015. Two follow-on spacecraft, configured to transmit up to 622 Mb/s, will be launched in early 2016.
Advances in micro/nanoelectronics have enabled unprecedented data collection and storage capabilities in spacecraft of all sizes. A current generation 15-megapixel color imager operating at 30 frames/s can generate over 10 gigabits/s (Gb/s) of raw data. Even operating in a framing mode, with non-overlapping frames, the data rate from a single camera can exceed 40 megabits/s (Mb/s) or 3600 Gb/day. Typical CubeSat systems are incapable of sending this amount of data to the ground in a useful time.
Laser communications, if advanced for these small systems, can achieve
Gb/s data rates enabling a broad range of high-data-rate CubeSat missions.
Space-to-ground optical links from LEO have already been demonstrated at data rates in excess of 5 Gb/s. However, these terminals have mass (>30 kg) and power (>100 W) requirements that are well beyond the limits of
CubeSats. Eliminating the mechanical gimbal and implementing bodypointing of the laser enables a significantly smaller, lighter optical terminal.
This approach takes advantage of the exceptionally low moments of inertia of CubeSats and their ability to perform rapid slew maneuvers.
Laser communication between satellites is now in its operational phase*.
Ground links are of interest for a number of applications ranging from
(feeder) links to GEO segments, direct to earth laser connections from LEO spacecrafts, and quantum key distribution from space platforms**. Tesat has been contracted by the German Space Agency DLR to build, test, and operate an optical ground station (TAOGS). This station enables research on the atmospheric channel at 1064nm by using the special feature of its counterpart, the Alphasat Laser Communication Terminal (LCT), to record and downlink LCT internal telemetry with a sampling rate of 25 kHz. Especially the direct detection of the acquisition sensors and of the coherent tracking sensors are useful information for channel modeling.
The measurement data from the space terminal can be correlated with the sensor recordings of the ground station having similar sampling rates.
Development and test of innovative codes optimized for atmospheric links as well as specialized acquisition and tracking strategies for the space segments are important tasks of the station in future
One special performance feature of the TAOGS is the correction of the atmospheric distortions by adaptive optics for the receive channel (data from space to ground) thus enabling the usage of large apertures and
9739-7, Session 2
Mark L . Stevens, Ronald R . Parenti, Matthew M . Willis,
Joseph A . Greco, Farzana I . Khatri, Bryan S . Robinson, Don
M . Boroson, MIT Lincoln Lab . (United States)
The Lunar Laser Communication Demonstration (LLCD) which flew on the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission achieved record uplink and downlink communication data rates between an earth-based ground terminal and a satellite orbiting the moon. In addition, the high-speed clocks of the communication system were used to accurately measure the round-trip time-of-flight (TOF) of signals sent to the moon and back to the Earth. The measured TOF data, sampled at a 20 kS/s rate, and converted to distance has been processed to show a Gaussian white noise floor typically less than 1 cm RMS. This resulted in a precision for relative
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Conference 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII distance measurements more than two orders of magnitude finer than the
RF-based navigation and ranging systems used during the LADEE mission.
This paper presents an overview of the TOF system and processing used in the experiment, a summary of the on-orbit measurements, and an analysis of the accuracy of the measured data for the mission. The mission data was collected and stored for off-line processing. But with specialized designs, future systems could perform in-situ real-time TOF calculations and data processing whenever a bi-directional lasercom link is established.
9739-10, Session 3
William T . Roberts, Jet Propulsion Lab . (United States) and
California Institute of Technology (United States); Sabino
Piazzolla, Thang Trinh, Vachik Garkanian, Lewis C . Roberts,
Malcolm W . Wright, Ryan Rogalin, Janet P . Wu, Loren P .
Clare, Arvid P . Croonquist, Jet Propulsion Lab . (United
States)
9739-8, Session 2
(Invited Paper)
Duy-Ha Phung, Etienne Samain, Nicolas Maurice,
Dominique Albanesse, Hervé Mariey, Mourad Aimar,
Gregoire Martinot-Lagarde, Observatoire de la Côte d’Azur
(France); Géraldine Artaud, Jean-Luc Issler, 3SNES -
French Space Agency (France); Nicolas Vedrenne, Marie-
Therese Velluet, ONERA, French Aerospace Lab (France);
Morio Toyoshima, Maki Akioka, Dimitar Kolev, Yasushi
Munemasa, Hideki Takenada, Naohiko Iwakiri &lt;naoiwakiri@nict .go .jp&gt;, NICT - Japanese National Institute of Information and Communication Technologies (Japan)
Optical Ground Station 1 (OGS1) is the first of a new breed of dedicated ground terminals to support NASA’s developing space-based optical communications infrastructure. It is based at NASA’s Optical
Communications Telescope Laboratory (OCTL) at the Table Mountain
Observatory near Wrightwood, CA. The system will serve as the primary ground station for NASA’s Laser Communications Relay Demonstration
(LCRD) experiment. This paper presents an overview of the OCTL telescope facility, the OGS1 ground-based optical communications systems, and the networking and control infrastructure currently under development. The
OGS1 laser safety systems and atmospheric monitoring systems are also described.
9739-11, Session 3
Eduard Y . Luzhanskiy, David Israel, Bernard Edwards,
NASA Goddard Space Flight Ctr . (United States)
The DOMINO project (Demonstrator for Optical teleMetry at hIgh data rate iN low earth Orbit) is conducted in collaboration between the French national center for space studies (CNES), the Cote d’Azur observatory
(Geoazur ? OCA), ONERA and the National Institute of Information and
Communications Technology (NICT). Geoazur is the project general contractor. DOMINO project aims to demonstrate the feasibility of a free-space optical communication link between SOTA (Small Optical
TrAnsponder), [1], [2], onboard SOCRATES microsatellite (launched on
May 24, 2014), and the MeO station, [3], located at Caussols, France. The main challenges of the project are the implementation of a complete laser communication from space to ground and the characterization of the turbulent atmosphere during the optical data transfer. The optical link between the SOCRATES satellite and the Meo Optical Ground Station (OGS) has been successfully established for all of 4 scheduled passes on June 22,
23, 28 (10 Mbps at 1549 nm) and July 21 (10 Mbps at 976 nm). During these passes, the average optical power, telecom signal and bit error rate have been continuously recorded at Meo OGS with different pupils (1.5 m, 0.4 m and 0.2 m diameter). In the presentation, we will first describe the Nasmyth optical bench with our monopixel ? detector for the scintillation and telecom signals measurements and then present some results of telecom and scintillation data analysis
NASA is presently developing first all optical high data rate satellite relay system, LCRD. To be flown on commercial geosynchronous satellite, it will communicate at DPSK and PPM modulation formats up to 1.244 Gbps.
LCRD flight payload is being developed by NASA’s Goddard Space Flight
Center. The two ground stations, one on Table Mountain in CA, developed by
NASA’s Jet Propulsion Laboratory and another on the Hawaiian island will enable bi-directional relay operation and ground sites diversity experiments.
In this paper we will report on the current state of LCRD system development, planned operational scenarios and expected system performance.
9739-12, Session 3
(Invited Paper)
Yoshikazu Chishiki, Shiro Yamakawa, Yutaka Takano,
Yuko Miyamoto, Tomohiro Araki, Hiroki Kohata, Japan
Aerospace Exploration Agency (Japan)
9739-9, Session 3
Bryan S . Robinson, Curt M . Schieler, Don M . Boroson, MIT
Lincoln Lab . (United States)
No Abstract Available
To meet increasing demands of high-speed data transmission, JAXA has started to develop a new optical data relay system. This system provides
1.8Gbit/s data relay service through optical inter-satellite link and Ka-band feeder link using a data relay satellite equipped with an optical terminal.
Target launch year of the optical data relay satellite is 2019 in Japanese fiscal year, and another optical terminal for LEO satellite and Ka-band ground stations are developed together.
This paper describes the development plan and the technologies of the optical data relay system.
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Conference 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII
9739-13, Session 4
Nicolas Vedrenne, Jean-Marc Conan, Cyril Petit, Vincent
Michau, ONERA (France)
To match the increasing need for high data rate between high altitude platforms and ground stations, Adaptive Optics for free space optics is investigated. Part of the interest is motivated by the need for coupling the received wave into a single mode fiber, to reap the benefits of the technological maturity of the fibered components. The Adaptive Optics correction must be effective in various conditions, sometimes unfavorable, i.e. in sites where atmospheric turbulence is strong, or with LEO satellites at potentially very low elevations. In Astronomy, the performance of Adaptive
Optics is characterized by average quantities such as average Strehl ratio or encircled energy. For free space communications, the fluctuation of the injection efficiency, with AO compensation, has to be statistically studied as well. It is investigated here for both links LEO-to-ground and GEO-toground. by thin ceramic-on-steel bearings, and controlled by embedded electronics aboard rigid-flex architecture.
9739-16, Session 5
Hemonth G . Rao, Catherine DeVoe, Andrew S . Fletcher,
Igor Gaschits, Farhad Hakimi, Scott A . Hamilton, Nicholas
D . Hardy, John Ingwersen, Rich D . Kaminsky, John D .
Moores, Marvin S . Scheinbart, Timothy M . Yarnall, MIT
Lincoln Lab . (United States)
No Abstract Available
9739-14, Session 4
Franck Marchis, Iris AO, Inc . (United States) and SETI
Institute (United States); Romain Fetick, SETI Institute
(United States); Daniel Asoubar, Christian Hellman,
LightTrans International UG (Germany); Thierry Fusco,
ONERA (France)
9739-17, Session 5
Andrew S . Fletcher, Nicholas D . Hardy, Scott A . Hamilton,
MIT Lincoln Lab . (United States)
No Abstract Available
We present a method to improve the beam quality of an outgoing sodium laser guide star beam, and also to create atmospheric multi-spots and complex shapes suitable for optimal adaptive optics corrections. A segmented MEMS deformable mirror controlled by 111 actuators is inserted in the beam of the laser to actively control the wavefront of the laser guide star in tip-tilt and also in piston. After calculating the optimal tip-tilt positions of each segment to reproduce a desired shape, we can reduce the effect of non-destructive and destructive interferences by modulating the segments in piston in random position up to a few kHz. The propagation through the instrument and the atmosphere was carefully simulated using
Virtual Lab and also our own Matlab-based code. Our simulation has been run to match the VLT’s laser guide star facilities. Such a simulation shows that the segmented MEMS Mirror can easily be inserted into an existing
LGS optical system, there is consequently no need to create a dedicated or expensive optical system for the use of our method. An optical setup was used to validate the method in a lab. We will discuss future applications of the beam splitting method for astronomy, as well as telecommunication and industrial applications.
9739-15, Session 4
Amnon G . Talmor, Facebook, Inc . (United States)
For links to/from high-altitude-platforms and between such platforms, a hemispherical two-axis gimbal with + 30? filed-of-regard and low aerodynamic drag has been designed. The design is based on is based on the Coude path, and is mechanically robust over +60?C to -80?C. Its mass is under 3Kg, including the optics bench that houses a fast steering mirror.
The design has been manifested onboard a carbon fiber and magnesium structure, motorized by permanent magnet motors, commutated by optical encoders, electrically connected via rotary slip-rings, rotationally aligned
9739-43, Session 5
Asher J . Willner, Yongxiong Ren, Guodong Xie, Long Li,
Yinwen Cao, Zhe Zhao, Peicheng Liao, Zhe Wang, Yan Yan,
Nisar Ahmed, Cong Liu, The Univ . of Southern California
(United States); Moshe Tur, Tel Aviv Univ . (Israel); Alan E .
Willner, The Univ . of Southern California (United States)
Free-space optical communications can play a significant role in line-ofsight links. In general, data can be encoded on the amplitude, phase, or temporal position of the optical wave. Importantly, there are environments for which ever-more information is desired for a given amount of optical energy. This can be accomplished if there are more degrees-of-freedom that the wave can occupy to provide higher energy efficiency for a given capacity (i.e., bits/photon). Traditionally, free-space optical links have used only a single beam, such that there was little opportunity for a wave to occupy more than one spatial location, thereby not allowing the spatial domain to be used for data encoding.
Recently, space- and mode-multiplexing has been demonstrated to simultaneously transmit multiple data-carrying free-space beams. Each spatially overlapping mode was orthogonal to other modes and carried a unique amount of orbital-angular-momentum (OAM).
In this paper, we consider that OAM modes could be a data-encoding domain, such that a beam could uniquely occupy one of many modes, i.e., 4 modes would provide 4 possible states and double the bits of information for the same amount of energy. In the past, such OAM-based encoding was shown at kHz data rates. We will present the architecture and experimental results for OAM-based data encoding for a free-space 1.55- ?m data link under different system parameters. Key features of the results include: (a) encoding on several modes is accomplished using a fast switch, and (b) low bit-error-rates are achieved at >Gbit/s, which is orders-of-magnitude faster than previous results.
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9739-18, Session 6
Conference 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII
L . Murphy, Christopher I . Moore, U .S . Naval Research Lab .
(United States)
Guangning Yang, NASA Goddard Space Flight Ctr . (United
States); wei lu, xiaoli sun, Jeffrey chen, Michael Krainak,
NASA Goddard Space Flight Ctr (United States)
We report an Innovative Free Space Optical Communication and
Navigation System which provides high data rate communication, precise measurements of spacecraft ranging, range rate, and accurate spacecraft pointing. A complete breadboard system was built. It includes both space and ground terminals. Along with 622MBPS data link, the following performances are achieved: two way ranging with 20um ranging and
10um/s range rate accuracy. This is accomplished through the Doppler frequency and data clock phase measurement.
This system opens a new way for science missions such as precision formation flight to measure the variation of the gravity field due to motions within the atmosphere, oceans, and solid body of different planetary bodies.
It also establishes an integrated service platform for optical navigation, which provides both communication and precision spacecraft ranging and range rate measurements, as well as the accurate spacecraft pointing.
The performance of free space optical (FSO) communication systems is strongly affected by optical scintillation. Scintillation fades causes can cause errors when the power on a detector falls below its noise floor, while surges can overload a detector. The very long time scale of scintillation compared to a typical bit in an FSO link means that error-correcting protocols designed for fiber optic links are inappropriate for FSO links.
Comparing the performance effects of different components, such as photodetectors, or protocols, such as FEC, in the field is difficult because conditions are constantly changing. On the other hand laboratory-based turbulence simulators, often using hot plates and fans, do not really simulate the effects of long-range propagation through the atmosphere.
We have investigated a different approach. Scintillation has been measured during field tests using FSO terminals by sending a cw beam through the atmosphere. A high dynamic range photodetector was digitized at a 5
KHz rate and files of the intensity variations were saved. Many hours of scintillation data under different environmental conditions and at different sites have been combined into a library of data.
A fiber-optic based scintillation playback system was then used in the laboratory to test modems and protocols with the recorded files. This allowed comparisons using the same atmospheric conditions allowing optimization of such parameters as detector dynamic range. It also allowed comparison and optimization of different error correcting protocols.
9739-19, Session 6
Anatoly Efimov, Los Alamos National Lab . (United States)
Numerous theoretical and not so numerous experimental works consistently prove that the performance of partially coherent beams (PCB) in free-space optical communication systems would surpass that of a fully coherent beam. This is because the scintillations of the PCB are typically lower than those of a coherent beam under appropriate selection of beam aperture and coherence radius. It was long believed, however, that partially coherent beams are difficult to modulate with data at high rates in the Gbps range.
This misconception is rooted in the practice of generating PCBs using rotating diffusers or SLM masks, which are inherently slow. An alternative method to generate PCBs involves simply coupling a reasonably, but not excessively, broadband light source into a short piece of multimode fiber.
By placing the standard LNBO modulator between the source and the fiber we demonstrate straightforward OOK modulation of the PCB at 1 Gbps, limited only by our electronics hardware. We propagate the modulated
PCB through a laboratory turbulence and measure resulting eye diagrams and compare them to those obtained with a coherent beam modulated in the same way. The quality of the PCB eyes is much better than those of the coherent beam as expected from a separate set of scintillation measurements. This simple experiment demonstrates the feasibility of PCBs for high-data rate free-space optical communication.
9739-21, Session 6
Timothy M . Yarnall, MIT Lincoln Lab . (United States);
Benjamin W . Horkley, MIT Lincoln Lab . (United States) and
Massachusetts Institute of Technology (United States);
Ajay S . Garg, Scott A . Hamilton, MIT Lincoln Lab . (United
States)
We present a demonstration of a high-rate photon counting receiver and spatial tracker based on a silicon Geiger-mode avalanche photodiode array
(GM-APD). This array enables sensitive high-rate optical communication in the visible and near infra red regions of the spectrum. The single photon response of the Geiger-mode detection process permits each array element to act as a photon counting receiver thereby providing sensitivity that approaches Shannon capacity limits for on-off keying and 16-ary pulse position modulation with strong error correction coding. The array contains
1024 elements arranged in a 32x32 pixel square. This large number of elements supports high data rates through the mitigation of blocking losses and associated data rate limitations created by the reset time of an individual Geiger-mode detector. Additionally, the array records the spatial coordinates of each detection event. By computing the centroid of the distribution of spatial detections it is possible to determine the angle-ofarrival of the detected photons. We demonstrate tracking of faint optical signals, sufficient to support links through a variety random media that introduce wavefront tilt. These levels of performance imply that Si GM-APD arrays are excellent candidates for a variety free space lasercom applications ranging from atmospheric communication in the 1 micron or 780 nm spectral windows to underwater communication in the 480 nm to 520 nm spectral window.
9739-20, Session 6
William S . Rabinovich, Rita Mahon, Mike S . Ferraro, James
9739-22, Session 7
Sylvain Poulenard, Airbus Defence and Space SAS
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(France); Jean-Marc Conan, ONERA (France); Bernard
Roy, Airbus Defence and Space SAS (France); Angélique
Rissons, Institut Supérieur de l’Aéronautique et de l’Espace
(France)
The main requirements for the next-generation of high throughput geostationary satellites are an annual link availability of 99.9%, a capacity around one Terabits/s and to be bent-pipe. An optical link, based on wavelength division multiplexing at 1.55
µ m, is a valuable alternative to overcome the limited data rata and the interference issues of conventional radio-frequencies. However, compared to RF links, optical links are much more sensitive to atmospheric effects such as cloud coverage and optical turbulence leading to important signal attenuation.
In this study, cloud obstruction is avoided thanks to a network of geographically spread optical ground stations connected to terrestrial fiber network. Concerning atmospheric turbulence, mitigation techniques are investigated to maximize the optical link budgets. For the downlink, power losses induced by the coupling of the optical signal into the single mode fiber of the receiver optical pre-amplifier are reduced by a fine pointing mirror that centers in real-time the intensity distribution in the core of the fiber. The uplink beam is pre-compensated with the same mirror to reduce the turbulence-induced pointing errors. The performance of such pre-compensation is derived by considering the decorrelation of the perturbations between the uplink and downlink directions that are separated by the pointing ahead angle.
Eventually, the achieved optical data rates in NRZ-DPSK are derived from the optical link budgets. We conclude that the described transparent optical feeder link system has a capacity ~600Gbps with an annual availability of 99.9%. Solutions are proposed to easily increase this capacity to one
Terabit/s.
9739-23, Session 7
Conference 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII
Yijiang Chen, Douglas S . Abraham, David P . Heckman,
Andrew Kwok, Bruce E . MacNeal, Kristy Tran, Janet P . Wu,
Jet Propulsion Lab . (United States)
(United States)
The paper will provide a brief introduction with literature survey of past and ongoing deep-space laser communications studies and programs. The key technology challenges will be enumerated that include: (i) acquisition tracking and pointing from deep-space ranges where Earth-ground-based transmitted laser beacon irradiances are weak and (ii) photon-efficient communications due the faint signal received and (iii) additive background noise at both ends of the link due to long durations of operating at shallow solar separation angles. The current strategies being pursued for mitigating these challenges will then be discussed and some examples of progress achieved so far will be reported. Studies related laser communication from the outer reaches of the solar system and inter-stellar space will be touched upon, Finally, a few examples of light science applications that advanced laser communication technologies can bring to bear will be described.
9739-25, Session 8
Rita Mahon, William S . Rabinovich, Peter G . Goetz, Marcel
W . Preussner, Mike S . Ferraro, James L . Murphy, U .S . Naval
Research Lab . (United States)
Components for free space optical communication terminals such as lasers, amplifiers, and receivers have all shrunk in both size and power consumption over the past several decades. However, pointing systems, such as fast steering mirrors and gimbals, have remained large and power-hungry.
Optical phased arrays provide a possible solution for non-mechanical beam steering that can be compact and lower in power. Silicon Photonics is a promising technology for phased arrays because it has the potential to scale to many elements and has compatibility with CMOS fabrication. For most free space optical communication applications, two-dimensional beam steering is needed. To date, Silicon photonic phased arrays have achieved two-dimensional steering by combining thermo-optic steering with wavelength tuning and an output grating. This architecture does not work for the receive function of an FSO link. We demonstrate steering using the thermo-optic effect for both dimensions.
A technology demonstration of free space optical communication at interplanetary distances is planned via one or more future NASA deepspace missions. Such demonstrations will “pave the way” for operational use of optical communications on future robotic missions with science payloads that generate large data volumes (e.g. synthetic aperture radar, hyperspectral imagers, large-pixel-area imagers, etc.). Human exploration missions to distant lunar orbits, asteroids, and Mars will also benefit from the large data volumes achievable with optical communications. Such optical communications capability will augment existing RF communications capability. Hence, the Deep Space Network (DSN) architecture will need to evolve in a manner that accommodates RF-only, combined-RF-and-optical, and optical-only missions. Preliminary attempts to model the anticipated future mission set and simulate how well it loads onto assumed architectures with combinations of RF and optical apertures have been evaluated. The evaluation reveals a number of potential architectural and operational trades between mission and ground infrastructure elements that continue to be studied. This paper discusses the results of preliminary loading simulations for hybrid RF-optical network architectures and highlight key mission and ground infrastructure considerations that emerge.
9739-24, Session 7
Abhijit Biswas, Joseph M . Kovalik, Meera Srinivasan,
Malcolm W . Wright, William H . Farr, Jet Propulsion Lab .
9739-26, Session 8
Mike S . Ferraro, William S . Rabinovich, Rita Mahon, U .S .
Naval Research Lab . (United States)
High sensitivity photodetectors serve two purposes in free space optical communication: data reception and position sensing for pointing, tracking, and stabilization. Because of conflicting performance criteria, two separate detectors are traditionally utilized to perform these tasks but recent advances in the fabrication and development of large area, low noise avalanche photodiode (APD) arrays have enabled these devices to be used both as position sensitive detectors (PSD) and as communications receivers.
Combining these functionalities allows for more flexibility and simplicity in optical assembly design without sacrificing the sensitivity and bandwidth performance of smaller, single element data receivers. Beyond eliminating the need to separate the return beam into two separate paths, these devices enable implementation of adaptive approaches to compensate for focal plane beam wander and breakup often seen in highly scintillated terrestrial and maritime optical links. While the Naval Research Laboratory and Optogration Inc, have recently demonstrated the performance of single period, InAlAs/InGaAs APD arrays as combined data reception and tracking sensors, an impact ionization engineered (I2E) epilayer design
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Conference 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII achieves even lower carrier ionization ratios by incorporating multiple multiplication periods engineered to suppress lower ionization rate carriers while enhancing the higher ionization rate carriers of interest. This work presents a three period I2E concentric, five element avalanche photodiode array rated for bandwidths beyond 1GHz with measured carrier ionization ratios of 0.05-0.1 at moderate APD gains. The epilayer design of the device will be discussed along with initial device characterization and high speed performance measurements. at high frequency (up to 2.5 Gbit/s) using a directly modulated 422nm
Gallium-nitride (GaN) blue laser diode with single longditudinal mode operation. In addition, we measure Gbit/s data transmission for AlGaInN laser diodes in plastic optical fibre (POF).
9739-27, Session 8
Michael A . Krainak, Guangning Yang, Xiaoli Sun, NASA
Goddard Space Flight Ctr . (United States); Wei Lu, ASRC
Federal Space and Defense (United States); Scott Merritt,
NASA Goddard Space Flight Ctr . (United States); Jeff
Beck, DRS Technologies, Inc . (United States)
9739-29, Session 9
Shantanu Gupta, Doruk Engin, Dave Pachowicz, Jean-
Luc Fouron, Juan Lander, Xung Dang, Slava Litvinovich,
Ti Chuang, Kent Puffenberger, Frank Kimpel, Rich Utano,
Fibertek, Inc . (United States); Malcolm W . Wright, Jet
Propulsion Lab . (United States)
We present performance data for novel photon counting detectors for free space optical communication. NASA GSFC is testing the performance of three novel photon counting detectors 1) a 2x8 mercury cadmium telluride
(HgCdTe) avalanche array made by DRS Inc... 2) a commercial 2880 silicon avalanche photodiode array and 3) a prototype resonant cavity silicon avalanche photodiode array. We will present and compare dark count, photon detection efficiency, wavelength response and communication performance data for these detectors. We discuss system wavelength trades and architectures for optimizing overall communication link sensitivity, data rate and cost performance.
The HgCdTe APD array has photon detection efficiencies of greater than
50% were routinely demonstrated across 5 arrays, with one array reaching a maximum PDE of 70%. High resolution pixel-surface spot scans were performed and the junction diameters of the diodes were measured.
The junction diameter was decreased from 31 ?m to 25 ?m resulting in a 2x increase in e-APD gain from 470 on the 2010 array to 1100 on the array delivered to NASA GSFC. Mean single photon SNR’s of over 12 were demonstrated at excess noise factors of 1.2-1.3.
The commercial silicon APD array has a fast output with rise times of 300ps and pulse widths of 600ps. Received and filtered signals from the entire array are multiplexed onto this single fast output.
The prototype resonant cavity silicon APD array is being developed for use at 1 micron wavelength.
Recent space lasercom demonstrations ? NASA LLCD mission and TeSat’s
GEO crosslink demonstration, point to the tremendous potential for space laser communication in providing high data-rate links for various NASA exploration missions. Increased bandwidth and increased ranges for asteroid and inter-planetary links require low SWaP, high power, laser transmitters.
For such photon-starved space optical links, a flexible format pulseposition-modulation (PPM) scheme provides high bits/energy efficiency.
We have developed a compact (10”x8”x2.4”, 7.5 lbs) and sealed, 1.5-um, polarization-maintaining, fiber laser transmitter sub-system, operating to
PPM-128 format at up to 6W for pulse slots from 0.5 to 8-nsec, with peak powers reaching 1 kW. An athermal design (only passive cooling) ensures high wall-plug efficiency (~15%). Functional testing has been completed for PPM formats ranging from PPM-16 to PPM-128, with pulse slots of 0.5,
1, 2, 4, and 8-nsec. Critical parameters such as extinction ratio is measured
>33-dB, polarization extinction >15-dB, spectral line-width <0.05-nm, and near diffraction limited beam-quality (M2 <1.2). This exceeds the laser source requirements for NASA’s inter-planetary missions.
The above laser transmitter is based on use of highly reliable 1.5-um fiber-optic telecom components to enable transition to formal space qualification. Thermal-vacuum cycling tests over 0-50’C range, for 300+ hours has confirmed all key specifications. Non-operational temperature cycling tests from -15 to +60 ‘C has also been verified. Vibration testing has been successfully conducted to a truncated GEVS profile (~10grms up to
700Hz). Radiation test comparison of a commercial and rad-tolerant 1.5-um high-power fiber amplifier, shows significant advantages for the latter, with
<12% power degradation at up to 20-krad of direct gamma-ray dosage.
These results provide the basis for formal TRL 6 space qualification of 1.5um, high-power, PPM fiber laser transmitter for NASA’s deep-space laser communication payload.
9739-28, Session 9
Stephen P . Najda, Piotr Perlin, Tadek Suski, Lucja
Marona, Michal Bockowski, Mike Leszczynski, Przemek
Wisniewski, Robert Czernecki, TopGaN Ltd . (Poland);
Robert Kucharski, Ammono S .A . (Poland); G . Targowski,
LopGaN Ltd . (Poland); Scott Watson, Anthony E . Kelly,
Univ . of Glasgow (United Kingdom); Malcolm A . Watson,
Paul M . Blanchard, Henry J . White, BAE Systems (United
Kingdom)
The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well. We consider the suitability of AlGaInN laser diode technology for free space laser communication, both airborne links and underwater telecom applications.
We measure visible light (free-space and underwater) communications
9739-30, Session 9
David O . Caplan, Robert T . Schulein, Mark L . Stevens, MIT
Lincoln Lab . (United States); Steven J . Spector, Draper
Lab . (United States)
Inadequate communication capacity increasingly limits space exploration efforts and the utility of airborne and satellite-based imaging systems. Freespace laser communications is known to have great potential to overcome this bandwidth bottleneck. While scalable wavelength division multiplexing
(WDM) techniques can easily support higher data rates, conventional transmitter implementations are often at odds with important design drivers for free-space systems such as good receiver sensitivity; low size, weight,
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and power (SWaP); and reduced implementation complexity. SWaP-efficient transmitters exist, but they are often limited to low 10 Mbit/s-class rates.
At Gbit/s-class rates, conventional methods for generating high-fidelity waveforms can require several watts per channel, making it prohibitively expensive to scale to numerous WDM channels.
In this paper, we describe the performance of versatile high-performance multi-rate WDM laser transmitters using next-generation compact highextinction-ratio power-efficient (CHERPe) transmitter designs. These leverage periodic time-frequency windowing of directly modulated laser signals to efficiently generate nearly ideal WDM waveforms with only mW-class drive power. This facilitates WDM-channelization and provides straightforward access to many THz of available optical spectrum with low-bandwidth electronics. Furthermore, this can support scalable multirate operation with good power- and photon-efficiency, enabling new architectural options and making this approach attractive for numerous applications and systems ranging from small airborne or CubeSAT-sized communication payloads to larger interplanetary lasercom platforms.
9739-31, Session 10
Conference 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII
Meera Srinivasan, Kenneth S . Andrews, William H . Farr,
Andre Wong, Jet Propulsion Lab . (United States)
In particular, implementing coherent combining using maximal-ratio combining resulted in a 6-dB SNR improvement over the mean SNR of the individual signals.
Future systems will also benefit from a common ground station architecture capable of supporting high and low data rates for near Earth and deep space communications, respectively. Block-repeating is a method that enables scaling data rate while maintaining a constant symbol rate by repeating blocks of symbols an integer number of times. Experimental results show a 45-dB scaling in data rate by block-repeating a PRBS sequence 36,017 times. This enabled scaling a BPSK signal with a channel rate of 11.52-GBd to 320-kb/s.
9739-33, Session 11
Xiaole Sun, Ivan B . Djordjevic, Mark A . Neifeld, The Univ . of
Arizona (United States)
For deep-space optical communications systems utilizing an uplink optical beacon, a single-photon-counting detector array on the flight terminal can be used to simultaneously perform uplink tracking and communications as well as accurate downlink pointing at photon-starved (pW/m^2) power levels. In this paper, we discuss concepts and algorithms for uplink signal acquisition, tracking, and parameter estimation using a photon-counting camera. Statistical models of detector output data and signal processing algorithms are presented, incorporating realistic effects such as Earth background and detector/readout blocking. Analysis and simulation results are validated against measured laboratory data using state-of-the-art commercial 32x32 photon-counting detector arrays, demonstrating submicroradian tracking errors under channel conditions representative of
Mars-range optical links.
9739-32, Session 10
David J . Geisler, Timothy M . Yarnall, Curt M . Shieler, Mark
L . Stevens, Bryan S . Robinson, MIT Lincoln Lab . (United
States)
Free-space optical (FSO) channels can be characterized by random power fluctuations due to atmospheric turbulence, which is known as scintillation.
Weak coherent source based FSO quantum key distribution (QKD) systems suffer from the scintillation effect because during the deep channel fading the expected detection rate drops, which then gives an eavesdropper opportunity to get additional information about protocol by performing photon number splitting (PNS) attack and blocking single-photon pulses without changing QBER. To overcome this problem, in this paper, we study a large-alphabet QKD protocol, which is achieved by using pulse-position modulation (PPM)-like approach that utilizes the time-frequency uncertainty relation of the weak coherent photon state, called here TF-PPM-QKD protocol. We first complete finite size analysis for TF-PPM-QKD to give practical bounds against non-negligible statistical fluctuation due to finite resources in practical implementations. The impact of scintillation under strong atmospheric turbulence regime is studied. The performance of TF-
PPM-QKD system get affected by channel fading caused by scintillation. We propose an adaptation method for compensating the scintillation impact.
By changing source intensity according to the channel state information
(CSI), obtained by classical channel, the adaptation method improves the performance of QKD system with respective to secret key rate. The CSI of a time-varying channel can be predicted using stochastic models, such as autoregressive (AR) models. Based on the channel state predictions, we change the source intensity to optimal value to achieve a higher secret key rate. We demonstrate that the improvement of the adaptation method is dependent on prediction accuracy.
9739-34, Session 11
Bhaskar Roy Bardhan, Jeffrey H . Shapiro, Massachusetts
Institute of Technology (United States)
The next generation free-space optical (FSO) communications infrastructure will require versatile ground stations capable of supporting multiple modulation formats while providing excellent sensitivity (i.e., photons-perbit). In addition, to minimize the size, weight, and power (SWaP) on spaceborne assets, the ground terminals need to efficiently scale to large effective collection areas. Recent advances in integrated digital coherent receivers enable the lossless coherent combining of signals from several smaller apertures to act as a single large effective aperture.
In this work, we experimentally demonstrate a next-generation ground station concept that relies digital signal processing based coherent combining (i.e., full-field addition) of signals received using four independent receive chains. Here, each receive chain consists of an aperture, a pre-amplified coherent receiver, and high-speed ADCs. Measured results show the effect of coherent combining a pulse carved 11.52-GBd BPSK waveform after transmission of one foot through a laboratory atmosphere.
Fiber-optic communications are moving to coherent detection in order to increase their spectral efficiency, i.e., their channel capacity per unit bandwidth. At power levels below the threshold for significant nonlinear effects, the channel model for such operation is a linear time-invariant filter followed by additive Gaussian noise, for which channel capacity is well known from Shannon’s noisy channel coding theorem. The fiber channel, however, is really a bosonic channel, meaning that its ultimate classical information capacity must be determined from quantum-mechanical analysis, viz. from Holevo-Schumacher-Westmoreland theorem. On a singlemode basis, the Holevo capacity of a linear (lossy or amplifying) channel with additive Gaussian noise was first established in [1] and later extended
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Conference 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII to a specialized memory channel in [2]. We provide a much more general continuous-time result, namely the Holevo capacity of a linear time-invariant
(LTI) bosonic channel with additive Gaussian noise arising from a thermal environment. In particular, we treat quasi-monochromatic communication under an average power constraint through a channel comprised of a stable
LTI filter that may be attenuating at all frequencies or amplifying at some frequencies and attenuating at others. Phase-insensitive additive Gaussian noise — associated with the continuous-time Langevin noise operator needed to preserve free-field commutator brackets — is included at the filter output. The resulting capacities, for several candidate filters, are compared with corresponding results for heterodyne and homodyne detection over the same channel to assess the increased spectral efficiency that might be realized with optimum quantum reception. Although motivated by the fiber application, our results are applicable to all LTI channels with additive phase-insensitive Gaussian noise.
[1] V. Giovannetti et al., Nature Photon. 8, 796-800 (2014).
[2] G. De Palma, A. Mari, and V. Giovannetti, Phys. Rev. A 90, 042312 (2014).
communication protocol called SuperDense Teleportation (SDT) can allow the reconstruction of a state without Bell-state measurements, enabling the protocol to succeed deterministically even for high dimensional qudits. This technique restricts the class of states transferred to equimodular states, a type of superposition state where each term can differ from the others in phase but not in amplitude; this restricted space of transmitted states allows the transfer to occur deterministically. We report on our implementation of
SDT using photon pairs that are entangled in both polarization and temporal mode. After encoding the phases of the desired equimodular state on the signal photon, we perform a complete tomography on the idler photon to verify that we properly prepared the chosen state. Beyond our tabletop demonstration, we are working towards an implementation between the International Space State and a ground telescope, to demonstrate the feasibility of space-based quantum communication. We will discuss the various challenges presented by moving the experiment out of the laboratory, and our proposed solutions to make SuperDense teleportation realizable in the space setting.
9739-35, Session 11
Alexander D . Hill, Bradley G . Christensen, Paul G . Kwiat,
Univ . of Illinois at Urbana-Champaign (United States)
Practical free-space optical quantum key distribution (QKD) faces many technical challenges. In marine environments (e.g., between ships), scattering, ship motion, and turbulence may limit or preclude the distribution of a secure cryptographic key. Multi-mode collection, either into a single-photon counter or arrays of detectors, necessarily introduces noise from dark counts and external factors, such as solar radiation. Additionally, polarization-only encodings may be subject to high bit error rates due to the relative motion of ships. Here we report on two techniques for the reduction of errors and losses for free-space quantum key distribution. First, we report on a transmission protocol which is resistant against transmit-receive errors in polarization-encoded QKD channels between ships. We show that the protocol is able to improve key rates over standard protocols in the regime where the data rate is too slow to update the reference frame of the transmission aperture. We then experimentally demonstrate a technique for the reduction of noise in multi-detector arrays for secure quantum key generation. The method does not require adaptive optics other than basic tip/tilt precompensation in the intermediate turbulence regime; in this technique, detectors which have a low probability of collecting signal photons are excluded from the QKD analysis (“selective deactivation”), which allows for a higher signal-to-noise ratio and quantum bit error rate.
We show that the technique improves QKD key generation rates in various noise and turbulence regimes.
9739-36, Session 11
Chris Zeitler, Trent Graham, Univ . of Illinois at Urbana-
Champaign (United States); Herbert Bernstein, Hampshire
College (United States); Paul G . Kwiat, Univ . of Illinois at
Urbana-Champaign (United States); Joseph Chapman,
Department of Physics, University of Illinois at Urbana-
Champaign (United States)
Establishing a quantum communication network would provide advantages in areas such as security and information processing. Such a network would require the implementation of quantum teleportation between remote parties. However, for photonic “qudits” of dimension greater than two, this teleportation always fails due to the inability to carry out the required quantum Bell-state measurement. A novel quantum
9739-37, Session PTue
Juraj Poliak, Dirk Giggenbach, Ramon Mata Calvo, Dominik
Bok, Deutsches Zentrum für Luft- und Raumfahrt e .V .
(Germany)
Effective coupling of the optical field from free-space to optical fiber is an essential prerequisite for modern free-space optical communications systems. It allows for easier system integration with active and passive optical fiber-coupled components as well as for efficient optical field mixing for coherent communications. While coupling into single-mode fiber provides an advantage of using low-noise erbium-doped fiber preamplifiers, its relatively small mode field diameter limits achievable fiber coupling efficiency. Coupling into multi-mode fiber (MMF) increases the fiber coupling efficiency, while introducing other spurious effects that authors have set out to analyze.
First the study of the free-space optical beam coupling in the context of satellite communications will be presented. Here, we assume satellite link scenarios with different elevations, which correspond to different index-ofrefraction induced turbulence (IRT) conditions. IRT gives rise to both the intensity and the phase deteriorations of the received optical field, which then give rise to speckle pattern in the focus of the receiver aperture. The speckle field is calculated by means of Fourier transform of the received field and is then used as the fiber launch field at the fiber input. Using dedicated modelling software, study of the fiber coupling efficiency, polarization preservation and high-order mode coupling in different multimode fibers will be carried out.
We further assume coherent mixing of two laser fields in MMF, e.g. in coherent communications or in transmitter-diversity systems. Theoretical investigation of the problem is followed by experimental verification demonstrating the practical implications of mode- and polarization-mixing phenomena.
9739-38, Session PTue
Aya Saito, Japan Women’s Univ . (Japan); Ayano Tanabe,
Makoto Kurihara, Nobuyuki Hashimoto, CITIZEN Holdings
Co ., Ltd . (Japan); Kayo Ogawa, Japan Women’s Univ .
(Japan)
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Conference 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII
The method for generating Laguerre Gaussian (LG) beams by using liquid crystal devices is easier than other methods. In this study, “quantized”
LG beams are generated from modulated Gaussian beams by using a combination of two liquid crystal devices: one is zone plate with six segments and the other is radial pattern with 24segments. The former generates the binary approximated amplitude of Laguerre function L(5,1) and the latter generates quantized vortex phase in 24 steps. In our previous work, it has been shown that intensity and phase distribution of quantized
LG beams are equivalent to those of LG beams in the Fraunhofer region.
While Free-space optics (FSO) is seriously affected by atmospheric turbulence. However, it is not clear whether quantized LG beams can treat as LG beams in atmospheric turbulence. In this paper, we numerically study the propagation properties of quantized LG beams through atmospheric turbulence using split-step beam propagation method and multiple phase screen method based on von Karman power spectrum model. For applying quantized LG beams to FSO, we evaluate propagation loss and scintillation index of quantized LG beams and LG beams changing propagation distances from 0m to 2000m and diameter of receiver aperture from 0.02m to 0.2m. As a results, quantized LG beams has same tendency as LG beams, therefore it is shown that quantized LG beams can treat as LG beam in atmospheric turbulence.
Wavefront estimation from slope value is an integral part in Shack–
Hartmann (S-H) type zonal wavefront sensors that are widely used to analyze the optical aberrations in application areas such as adaptive optics, phase imaging, visual optics and so on. Using a particular estimation algorithm, these measured slopes are converted into wavefront phase values. Hence, accuracy in wavefront estimation lies in proper interpretation of these measured slope values using an appropriate estimation algorithm.
One of the important sources of error in a basic wavefront estimation process is the algorithm discretization error which depends on the basic estimation scheme adopted. Basically, this type of error is a consequence of the finite sampling geometry. Algorithm discretization error plays an important role and is needed to be considered in choosing a particular estimation geometry as it determines how well a particular estimation process reconstructs a phase of different shape. In this paper, we investigate the algorithm discretization error in the Southwell as well as in an improved zonal phase gradient model which can be considered as a five point and nine point stencil respectively. Both the estimation algorithms are modeled using Taylor series expansion to show the order of discretization error and finally make a comparison of the improved model with the standard
Southwell model in terms of error propagation.
9739-39, Session PTue
Byung Jae Chun, Nanyang Technological Univ .
(Singapore); Hyun Jay Kang, KAIST (Korea, Republic of);
Young-Jin Kim, Nanyang Technological Univ . (Singapore);
Seung-Woo Kim, KAIST (Korea, Republic of)
Generating multiple optical frequencies referenced to frequency standards is an important task in optical communication, clock dissemination, and precision LIDAR. An apparatus for frequency-comb-referenced generation of multiple optical frequencies is demonstrated and applied to high-precision free-space transfer of multiple optical frequencies. For the purpose, a single optical mode is extracted out of the frequency comb at each channel and its power is amplified from a tens nW to 10 mW using diode laser injection locking. Different optical frequencies can be selected out of the broadband frequency comb in parallel, which contains hundreds of thousands modes in 50 nm bandwidth around the central wavelength of 1550 nm. The relative linewidth and frequency instability at each channel corresponds to (instrument-limited) sub-1 Hz and 2.35?10^-15 at 10 s averaging time, respectively. During the free-space transfer of multiple optical frequencies over a 1.4-km long test-bed, the atmospheric disturbances caused phase and frequency noise which results in linewidth broadening and center frequency shift. These noise components are precisely monitored and compensated using the heterodyne beat frequency between the frequencyshifted reference beam and the partial-reflected measurement beam passed through the free-space optical path; then, an acousto-optic modulator is used as the feed-back control servo with the aid of the radio-frequency phase-locked-loop. The relative stability after the free-space transfer is
5.73?10^-18 at 10 s averaging time. This confirms that the proposed system transfers multiple optical frequencies with high precision to remote outdoor sites.
9739-41, Session PTue
Syed J . Hussain, Abir Touati, Qatar Univ . (Qatar);
Abderrazak Abdaoui, QATAR UNIVERSITY (Qatar); Farid
Touati, Qatar Univ . (Qatar)
Free-Space Optics (FSO) is a wireless technology that enables the optical transmission of data though the air. FSO is emerging as a promising alternative or complementary technology to fiber optic and wireless radio-frequency (RF) links due to its high-bandwidth, robustness to EMI, and operation in unregulated spectrum. These systems are envisioned to be an essential part of future generation heterogeneous communication networks. Despite the vibrant advantages of FSO technology and the variety of its applications, its widespread adoption has been hampered by rather disappointing link reliability for long-range links due to atmospheric turbulence-induced fading and sensitivity to detrimental climate conditions.
A major challenge of such systems is to provide a strong backup system with soft-switching capabilities when the FSO link becomes down. Using the same medium for backup will not help, in the case of the link cut, because most likely the same technology will be cut as well. This is the reason why we decided to create a different medium RF as a backup.
The specific objective of this work is to study for the first time in Qatar and the GCC the link capacity, link availability, and link outage of an FSO system with RF back up (i.e. hybrid FSO/RF) under harsh environment.
In order to analyze the two transport media, we have ported Embedded
Linux on FPGA (Field Programmable Gate Array) and designed a network sniffer application that can run into FPGA. We installed new FSO/RF terminals and configure and align them successively. In the reporting period, we carry out measurement and relate them to weather conditions. The experimental results, when compared to studies which have been carried out before in Europe and North America, show different behavior.
9739-40, Session PTue
Biswajit Pathak, Bosanta R . Boruah, Indian Institute of
Technology Guwahati (India)
9739-42, Session PTue
Omer Porat, Joseph Shapira, Soreq Nuclear Research Ctr .
(Israel)
We have compared measured angle-of-arrival (AOA) fluctuations to the prediction of various models, for a laser beam propagating through a turbulent atmosphere at ground level.
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Conference 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII
Three models have been investigated: a simple small perturbation model, a model which incorporates also inner and outer scale effects and a third model (Ma Jing et al 2007 Chinese Phys. 16 1327) which takes into account the contribution of additional spatial scales and is able to predict a saturation regime.
Data were collected in an approximately ten year time span. We have used near infra-red LIDAR systems to determine the AOA fluctuations by measuring the short term movement of a laser spot in the receiver plane, reflected from targets placed at various distances. In parallel, we have also measured the turbulence strength with a short-range scintilometer and recorded the average wind speed along the laser path.
Our analysis indicates that the third model is able to predict the general behavior of the AOA fluctuations even as it approaches the saturation regime, while the simple model provides a valid forecast only in limited conditions of weak turbulence and short distances. In addition, we observe some differences between the day and night behavior which wasn’t considered by any of the models.
Our talk includes a review of the three models and a description of the measurement’s setup which will be followed by an in depth discussion of the results of the field evaluation.
9739-44, Session PTue
Tomohiro Araki, Japan Aerospace Exploration Agency
(Japan)
It requires higher-rate data transmission system that improvements of earth observation satellite performance and increasing of their production data.
Therefore, optical data relay system have been investigating and developing in Europe, US and Japan. Japan Aerospace Exploration Agency (JAXA) has started it’s Data Relay Optical System (DROS) program. DROS program applying DD-DPSK technique for modulation and demodulation. As well known, demodulation of DD-DPSK is based on Delay Line Interferometer
(DLI), therefore it is difficult to have multi channel-rate performance for DD-
DPSK demodulator.
Authors have been investigating digital coherent receiver technique for onboard receiver for future space optical communication system of Japan.
Digital coherent technologies, which are composed of coherent detection and digital signal processing, are confirmed to possibly increase the signal speed, improve the receiver sensitivity and extend the tolerance for Doppler frequency shift. We will report some experimental results with 2.5Gbps
DBPSK signal light, as well as the future issues for implementation. Authors confirm digital coherent receiver has richer expandability than other detection technique. As a facet of expandability, a concept of multi channelrate receiver using digital coherent technique is introduced.
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9740-1, Session 1
(Invited Paper)
Valeria Caprettini, Gabriele C . Messina, Michele Dipalo,
Rosanna La Rocca, Andrea Cerea, Francesco De Angelis,
Istituto Italiano di Tecnologia (Italy)
Biological systems are analysed mainly by optical, chemical or electrical methods. Normally each of these techniques provides only partial information about the environment, while combined investigations could reveal new phenomena occurring in complex systems such as in-vitro neuronal networks. Aiming at the merging of optical and electrical investigations of biological samples, we introduce three-dimensional plasmonic nanoantennas for SERS (Raman) spectroscopy integrated on the electrodes of electronic biosensors, namely MEAs (Multi-electrode arrays), thus integrating very sensitive spectroscopy and electrical acquisitions with the same tool.
Nanoantennas are produced on MEAs using a novel ion beam based technique previously introduced[1,2]. SERS spectroscopy as well as electrical recording were performed on living neurons cultured on MEA and immersed in their media.
The SERS measurements show a much higher sensitivity when performed on the tip of the nanoantenna in respect to the flat substrate[3]; this effect is a combination of the high plasmonic field enhancement and of the tight adhesion of cells on the nanoantenna tip. Spectra acquired on the nanoantenna show distinctive peaks of relevant biomolecules of the cell membranes.
Neuronal activity could be monitored using the same MEAs with nanoantennas fabricated on the electrodes. Neurons could be cultured on these devices for up to one month, and electrical recordings performed at different growth stages showed a healthy development of the network.
Moreover we show that when combined with ultra-short laser pulses our plasmonic nanotube can be used to deliver a broad range of molecules into the intracellular compartment in a controlled way and without side-effects
[4].
References:
[1] F. De Angelis, M. Malerba, M. Patrini, E. Miele, G. Das, A. Toma, R. P.
Zaccaria, E. Di Fabrizio, Nano Lett. 2013, 13, 3553.
[2] M. Dipalo, G. C. Messina, H. Amin, R. La Rocca, V. Shalabaeva, A. Simi, A.
Maccione, P. Zilio, L. Berdondini, F. De Angelis, Nanoscale 2015, 7, 3703.
[3] R. La Rocca, G. C. Messina, M. Dipalo, V. Shalabaeva, F. De Angelis, Small
2015, 11, 4632.
[4] G. C. Messina et al, Advanced Materials 2015, in press.
9740-2, Session 1
Michel Meunier, Adrien Dagallier, Remi Lachaine, Christos
Boutopoulos, Étienne Boulais, Ecole Polytechnique de
Montréal (Canada)
Plasmonic nanoparticle (NP)-enhanced laser nanobubbles are an efficient tool to interact locally with biological structures. Potential applications span a wide range of biomedical research fields, including cancer treatment, bioimaging and gene delivery. Fundamental mechanisms controlling the cavitation onset and dynamics are highly dependent on the type of NP used and are yet not totally understood. In this presentation, we compare cavitation issued from two extreme cases: in-resonance and off-resonance plasmonic NPs.
For off-resonance NPs, we show that cavitation is controlled by the production and relaxation of a nanoplasma generated by the non-linear absorption of the plasmon-enhanced laser near-field, leaving NPs intact.
In addition, time-resolved spectroscopy and nanobbuble imaging shows a strong correlation between the cavitation threshold of different NPs sizes and their calculated near-field enhancement. Further modeling of the laser-NP interaction and bubble dynamics suggest that the cavitation threshold is related to the generation of a critical volume of plasma reaching a critical electron density. Plasma relaxation drives water molecules into a supercritical state that subsequently results in the formation of a nanoscale bubble.
For in-resonance NPs, an intricate combination of heating and plasma effects controls cavitation. Shadowgraphic imaging and modeling results suggest that nanobubble formation arises both from heat transfer from the hot particle and plasma relaxation in the water surrounding in-resonance core-shells. For ultrafast pulses, our work suggests that a near-field generated plasma contributes significantly to the cavitation, whereas thermionic emission from the hot particle dominates for longer picosecond pulses.
9740-3, Session 1
Nabiha Saklayen, Harvard Univ . (United States); Marinus
Huber, Ludwig-Maximilians-Univ . München (Germany);
Marinna Madrid, Daryl I . Vulis, Harvard Univ . (United
States); Weilu Shen, Rensselaer Polytechnic Institute
(United States); Valeria Nuzzo, ECE Paris (France); Eric
Mazur, Harvard Univ . (United States)
We use pulsed laser-excited plasmonic micropyramids to deliver molecules to living cells with high efficiency, viability, and throughput. Cellular therapy holds great promise for applications in gene therapy and fundamental biomedical research, and it is essential to develop a universal delivery platform that can safely deliver biomolecules to different cell types effectively. Our micropyramids produce a strong plasmonic effect under laser illumination by focusing energy in a small volume at the tip of each pyramid.. This leads to the formation of microbubbles which temporarily porate the cell membrane and allow dye molecules and siRNA to diffuse into the cytoplasm. We fabricate large-area micropyramid arrays using photolithograpy, anisotropic etching of silicon, metal deposition, and template stripping. The silicon pyramid templates can be used repeatedly to fabricate gold pyramids. We optimize our laser parameters for high efficiency delivery of small dye molecules like calcein (>80%) at high cell viability (>90%) for different cell lines, and use fluorescence microscopy and flow cytometry to study a large number of cells. Alongside small dyes, we also deliver different-sized fluorescently labeled dextrans (70kDa-2000kDa) and fluorescent microspheres. We deliver siRNA to GFP-expressing cells to observe gene knockdown and use western blot analysis to confirm
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Conference 9740: Frontiers in Ultrafast Optics:
Biomedical, Scientific, and Industrial Applications XVI the expression. Our method delivers molecules with high efficiency and high cell viability in different cell types, and our substrates can be reused for repeated high efficiency poration. Our scalable technique offers an innovative approach to delivering molecules to living cells for important applications in regenerative medicine. and micromanipulation of the bone marrow in vivo. I will also discuss outstanding challenges and further development of nonlinear optical techniques for biological studies at multiple spatial and temporal scales.
9740-4, Session 1
Christos Boutopoulos, Adrien Dagallier, Maria Sansone,
Évelyne Lecavalier-Hurtubise, André-Pierre Blanchard-
Dionne, Ecole Polytechnique de Montréal (Canada); Ali
Hatef, Nipissing Univ . (Canada); Michel Meunier, Ecole
Polytechnique de Montréal (Canada)
9740-6, Session 2
Ruth Houbertz, Multiphoton Optics GmbH (Germany);
Soenke Steenhusen, Kerstin Obel, Herbert Wolter,
Fraunhofer-Institut für Silicatforschung (Germany);
Joachim Nickel, Heike Walles, Universitätsklinikum
Würzburg (Germany)
Plasmonic nano-bowties (NBTs) have the unprecedented ability to concentrate light to deep sub-wavelength volumes and have been used for applications such as, surface-enhanced Raman spectroscopy, optical trapping and single molecule fluorescence. NBTs are highly polarizable nanostructures, thus enabling precise spatial control of near-field enhancement by simply changing the polarization of the excitation light.
In this work, we used NBTs-enhanced near-infrared femtosecond (fs) laser pulses to generate plasmonic bubbles in liquids and control their nucleation sites with nanoscale spatial precision. We employed modeling to optimize the NBTs response at the near-infrared. Optimized arrays of gold NBTs were fabricated on ITO coated glass substrates by electron beam lithography.
Upon fs laser excitation (70-120 mJ/cm2) in liquid NBTs generated submicron bubbles, which were detected by ultrafast imaging. Following the bubble generation we evaluated experimentally the distribution of the nucleation spots by scanning electron microscopy (SEM) of the resulting
NBTs morphology. SEM observations, in agreement with nanoplasma simulations, indicated that the induction of nanoscale bubble nucleation spots (simulated diameter: 20-50 nm) occurs at high-near field regimes (|E/
E0|: 4 to 8) around the NBTs. The spatial distribution of those nucleation spots can be controlled by changing the polarization of the incident laser beam. Furthermore, we observed a sharp threshold (70 mJ/cm2) for the transformation of the NBTs to spherical nanoparticles. The latter, coincides with the nanobubble generation threshold, indicating that the nanoplasma generation and the dynamic bubble evolution are the main causes of the
NBTs morphology alteration. Our results indicate that the excitation of NBTs with polarized light is a unique method to generate and spatially control pressure stimulus in the nanoscale. This can find applications in fields such as, cellular stimulation and nanofabrication.
9740-5, Session 2
(Invited Paper)
Charles P . Lin, Massachusetts General Hospital and Harvard
Medical School (United States)
Optical technologies cover a broad range of applications which make use of the generation and the manipulation of light, and they open up a wide field of novel applications when combined with electronics or biologics.
Many efforts have been made to develop laser light sources in order to continuously increase their application potential. The interaction of ultrashort laser pulses with polymer or glass materials is of high technological interest. Since the triggered reactions are strongly confined to the focal region, the formation of free-form 3D-printed micro and nano structures can be easily carried out with highest precision.
For biological applications, the appeal of this method is an intrinsic scalability strongly improving the fabrication of, e.g. microfluidic cells, scaffolds for tissue engineering approaches, or drug delivery systems.
For the restoration of diseased or damaged tissue the growth of cells on
3D porous scaffolds for tissue engineering (TE) is a promising approach to generate autologous tissue. Scaffold structures should not only have microscopic feature sizes, but also large overall sizes fabricated from biocompatible or biodegradable materials. Appropriate types of functionalization additionally create binding sites for, e.g. biomolecules and/ or cells, thus enabling a precise control of cell adhesion, spreading, growth, and differentiation. The scalability of the method ranging from the sub-100 nm regime to the cm range is demonstrated, and the influence of structure type and size has been shown already for primary human microvascular endothelial cells.
9740-7, Session 2
Mitsuhiro Terakawa, Keio Univ . (Japan); Maria Leilani Y .
Torres-Mapa, Leibniz Univ . Hannover (Germany); Dag
Heinemann, Anton Hördt, Laser Zentrum Hannover e .V .
(Germany); Yasutaka Nakajima, Keio Univ . (Japan); Nikolay
N . Nedyalkov, Bulgarian Academy of Sciences (Bulgaria);
Heiko Meyer, Tammo Ripken, Laser Zentrum Hannover e .V . (Germany); Alexander Heisterkamp, Leibniz Univ .
Hannover (Germany) and Laser Zentrum Hannover e .V .
(Germany)
The bone marrow (BM) is a unique microenvironment where hematopoietic stem cells (HSCs) reside and differentiate to form all blood cell types (red blood cells, white blood cells, and platelets). The BM is also a location where hematologic malignancies (leukemia, multiple myeloma) originate, as well as a common site for solid tumors metastasis. Studies of cellular organization within the BM is important for improving HSC engraftment after BM transplantation, and for targeting cancer cells that often acquire resistance to therapy when sheltered in the BM microenvironment.
However BM has been difficult to image due to its complex structure and anatomic location embedded within the bone matrix. I will discuss recent advances in nonlinear optical techniques applied to imaging, sensing,
Hydrogels are promising biomaterials for wearable devices, implants, and scaffolds in tissue engineering because of their high flexibility, permeability for molecules, and biocompatibility. Growing interest aroused in recent years in the combination of a metal structure and a hydrogel for biooptolelectronic devices. In this study, we have demonstrated the fabrication of silver microwires within a hydrogel by multi-photon-induced reduction of silver ions using femtosecond laser irradiation. Near-infrared femtosecond laser pulses at a repetition rate of 80 MHz were focused in poly(ethylene glycol) diacrylate (PEGDA) hydrogel, a synthetic polymer-based hydrogel suitable for practical production with controlled properties, in the presence of silver ions. A silver wire approximately 1 micrometer in diameter was fabricated by scanning laser beam. The estimated laser intensity at the
182 SPIE Photonics West 2016 · www.spie.org/pw
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focal point is far less than the threshold for refractive index change of hydrogel. Because the hydrogel is transparent for 800 nm wavelength, the focal position is easy to be changed, which enables us to fabricate 3D structures. Unlike other methods such as lithography-based techniques, our method provides direct writing of 3D metal structure both in connected and disconnected form inside a hydrogel, which is promising for fabricating biooptoelectronic devices.
9740-8, Session 2
Conference 9740: Frontiers in Ultrafast Optics:
Biomedical, Scientific, and Industrial Applications XVI
Jessica Zeman, Kevin Eliceiri, Andreas Velten, Univ . of
Wisconsin-Madison (United States) be demonstrated. In particular, a feedback operation process is implemented in the DUPS to ensure a robust and repeatable shaping process.
9740-56, Session 2
Peter M . Gruber, M . Markovic, K . Hoelzl, M . Tromayer,
Jürgen Stampfl, Robert Liska, Aleksandr Ovsianikov,
Technische Univ . Wien (Austria)
Non-line-of-sight imaging uses photon time of flight to reconstruct images from light that has undergone multiple diffuse reflections and making it possible to image scenes without a direct line of sight. Among the image reconstruction methods available for this technique, the filtered backprojection provides the highest speed, is suitable for large scenes because of moderate memory requirements, and does not require prior knowledge about the scene. We project picosecond laser pulses on points on a visible relay surface and image light that scatters from these illumination points to the hidden scene and back to different points on that relay surface. Using the information about the position of the illumination and collection spots on the relay surface as well as the time of flight between those spots we reconstruct an image of the hidden scene.
The reconstructed image resulting from a non-line-of-sight imaging experiment exhibits a complex point spread function that varies across the reconstruction volume and depends on the pattern of projected and imaged spots on the relay surface. To improve our reconstruction quality we apply iterative backprojection approaches, where the result of the first backprojection is used to compute an improved second backprojection.
We also provide a point spread function decomposition method to improve reconstructions after the backprojection. Finally we attempt to create a filtered backprojection analogous to the filtered backprojection used in computed tomography reconstructions.
We present reconstructions of improved quality approaching the theoretical limit for backprojection techniques and analyze their resolution.
Conventional 2D cell culture systems used in biology do not accurately reproduce the 3D structure, function, or physiology of living tissue.
Resulting behaviour and responses of cells often differ substantially from those observed within natural extracellular matrices (ECM). 3D printing of cell-containing hydrogel structures opens exciting perspectives for the engineering of 3D biomimetic cell culture matrices. In this context multiphoton processing is an outstanding approach as it offers spatial resolution unmatched by other 3D printing methods, while providing a possibility to produce structures in the presence of living cells [1].
Development of cell compatible and photopolymerizable hydrogels is an important step towards the latter goal [2]. Current challenges include possible cell damage, resulting from generation of free radicals, and necessity for faster processing [3]. In this contribution the recent progress on multiphoton processing of cell-containing hydrogel constructs is presented. Our results indicate the general practicability of this approach for fabrication of 3D cell-containing structures. The further development of the multiphoton processing techniques will facilitate the realization of elegant biological in vitro experiments, helping to elucidate biomimetic aspects of cell interaction with the surrounding environment.
[1] A. Ovsianikov, V. Mironov, J. Stampf, and R. Liska, Engineering 3D cellculture matrices: multiphoton processing technologies for biological and tissue engineering applications, Expert Rev. Med. Devices 9(6), 613–633
(2012) [doi:10.1586/erd.12.48]
[2] J. Torgersen, X.-H. Qin, Z. Li, A. Ovsianikov, R. Liska, and J. Stampfl,
Hydrogels for Two-Photon Polymerization: A Toolbox for Mimicking the Extracellular Matrix, Adv. Funct. Mater. 23(36), 4542–4554 (2013)
[doi:10.1002/adfm.201203880].
[3] A. Ovsianikov, S. Mühleder, J. Torgersen, Z. Li, X.-H. Qin, S. Van
Vlierberghe, P. Dubruel, W. Holnthoner, H. Redl, R. Liska, and J. Stampfl,
Laser Photofabrication of Cell-Containing Hydrogel Constructs, Langmuir,
131010115717001 (2013) [doi:10.1021/la402346z].
9740-9, Session 2
Yina Chang, Chenglin Gu, Dapeng Zhang, Shih-Chi Chen,
The Chinese Univ . of Hong Kong (Hong Kong, China)
9740-10, Session 3
(Invited Paper)
Ben Leshem, Weizmann Institute of Science (Israel)
We report a Digital micromirror device (DMD)-based Ultrafast Pulse Shaper, i.e. DUPS, for femtosecond laser arbitrary phase and amplitude shaping—the first time a programmable binary device reported to simultaneously shape the phase and amplitudes of ultrafast pulses spectrum at up to 32 kHz rate over a broad wavelength range. The DUPS is highly efficient, compact, and low-cost based on the use of a DMD in combination with a transmission grating. We will first present the optical configuration and design process of
DUPS, followed by carefully designed experiments demonstrating arbitrary phase and amplitude shaping capability as well as high-speed pulseshaping at 4.2 kHz. In the experiments, spatial and temporal dispersion introduced by the DUPS is compensated by a quasi-4-f setup and a grating pair respectively. For phase shaping, double pulses are generated in order to validate the effectiveness of DUPS and to calibrate the system. Next, arbitrary phase shaping capability will be demonstrated by continuous tuning of GVD and modulation of half spectrum shifted by π . For amplitude shaping, femtosecond pulses with arbitrary spectrum shapes, including rectangular, sawtooth, triangular, double-pulse, and exponential profile, will
A decade ago temporal focusing (TF) was suggested as an axially resolved multi-photon microscopy technique. In recent years TF has found applications in a large number of fields beyond microscopy. Basically, any technique that requires axially confined multi-photon excitation without tightly focusing the light beam can potentially benefit from TF.
Indeed, applications range from optical lithography to tissue ablation and optogenetics. Furthermore, it was shown that TF exhibits an enhanced robustness to scattering due to propagation in scattering medium. I will review the physical principles and limitations of TF and its robustness to scattering and describe some of its applications.
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9740-11, Session 3
Tuan Le, FEMTOLASERS Produktions GmbH (Austria);
André Müller, Bernd Sumpf, Ferdinand-Braun-Institut
(Germany); Ole B . Jensen, Technical Univ . of Denmark
(Denmark); Anders Kragh Hansen, Department of
Photonics Engineering, Technical University of Denmark
(Denmark); Peter E . Andersen, Technical Univ . of Denmark
(Denmark)
Diode-pumping Ti:sapphire lasers promises a new approach to low-cost femtosecond light sources. Thus in recent years a lot of effort has been taken just to overcome the quite low power and low beam qualities of available green diodes to obtain output powers of several hundred milliwatts from a fs-laser. In this work we present an alternative method by deploying frequency-doubled IR diodes with decent beam qualities to pump fs-lasers.
The revolutionary approach allows choosing any pump wavelengths in the green region and avoids complicated relay optics for the diodes. For the first time we show results of a diode-pumped 8 fs laser and how a single diode setup can be integrated into a 30 x 30 cm? fs-laser system generating sub
20 fs laser pulses with output power towards half a Watt. This technology paves the way for a new class of very compact and cost-efficient sub 20 fs lasers for life science and industrial applications.
9740-12, Session 3
Conference 9740: Frontiers in Ultrafast Optics:
Biomedical, Scientific, and Industrial Applications XVI
Seung Ryeol Oh, KAIST (Korea, Republic of); Joo Hyun
Park, Korea Research Institute of Standards and Science
(Korea, Republic of); Won Sik Kwon, Jin Hwan Kim,
Kyung-Soo Kim, KAIST (Korea, Republic of); Jae Yong Lee,
KRISS (Korea, Republic of); Soohyun Kim, KAIST (Korea,
Republic of)
9740-13, Session 3
Alma Fernández, Aart Verhoef, Medizinische Univ . Wien
(Austria) and Technische Univ . Wien (Austria); Marco
Andreana, Medizinische Univ . Wien (Austria); Martin
Distel, St . Anna Kinderkrebsforschung e .V . (Austria);
Kim G . Jespersen, Thomas V . Andersen, NKT Photonics
A/S (Denmark); Lingxiao Zhu, Univ . Wien (Austria) and
Technische Univ . Wien (Austria); Tobias Flöry, Andrius
Baltuska, Technische Univ . Wien (Austria); Wolfgang
Drexler, Angelika Unterhuber, Medizinische Univ . Wien
(Austria)
We apply a monolithic Yb-fiber chirped pulse amplifier, that uses a dispersion matched fiber stretcher and a spliced-on hollow core photonic bandgap fiber compressor, for multimodal nonlinear microscopy. By varying the repetition rate of the amplifier, different output pulse energies can be obtained to adjust signal, data-acquisition speed and resolution. 7 nJ, 230 fs pulses are obtained at a repetition rate of 49 MHz. At 2.45 MHz repetition rate 77 nJ, 220 fs pulses with 92% of the energy contained in the main pulse, can be obtained with minimal nonlinearities in the system. At 1 MHz, 135 nJ pulses are obtained with 226 fs duration and 82 percent of the energy in the main pulse. Due to the good dispersion match of the stretcher to the hollow core photonic bandgap fiber compressor, the duration of the output pulses is within 10% of the Fourier limited duration, independent of the chosen repetition rate. Since the pulses are compressed in a fiber, this source is especially suited for incorporation in endoscope-based microscopy.
With this source we perform in-vivo nonlinear microscopy in zebrafish larvae, where we simultaneously measure second and third harmonic generation and fluorescence from two-photon excited red-fluorescent protein. Strong second harmonic signal can be observed from the collagen fibers in the tail finn, as well as from muscles and forming bone in a zebrafish tail. Fluorescence from macrophages labeled with mCherry, that can be used to identify cancer, is also observed
Single pulse coherently controlled nonlinear Raman spectroscopy is the simplest method among the coherent anti-Stokes Raman spectroscopy systems. In recent research, it has been proven that notch shaped femtosecond pulse laser can be used to collect the coherent anti-Stokes
Raman signals. In this study, we showed single-pulse coherent anti-Stokes
Raman spectroscopy via fiber Bragg grating which is the simplest notch filtering component on the femtosecond pulse lasers. The experiment is performed incorporating a commercialized femtosecond pulse laser system
(MICRA, Coherent) with a 100 mm length of 780-HP fiber which is inscribed
50 mm of Bragg grating. The pump laser for coherent anti-Stokes Raman spectroscopy has a bandwidth of 80 nm and central wavelength of 800 nm with a notch shaped at 785 nm. The positive chirped pulse is compensated by chirped mirror set. We compensate almost 26000 fs^2 of positive group delay dispersion for the transform-limited pulse at the sample position.
Finally, coherent anti-Stokes Raman signals are observed using an Olympus
IX81 microscope and a spectrometer (Jobin Yvon iHR320 and TE-cooled
Andor Newton EMCCD). We obtain coherent anti-Stokes Raman signals of acetone samples which have Raman peak at the spectral finger-print region. The experimental results are consistent with the simulation results of
3rd order polarization signals. In conclusion, the proposed method is more simple and cost-effective than the methods of previous research which use grating pairs and resonant photonic crystal slab. Furthermore, the proposed method can be used as endoscopy system.
9740-16, Session 4
Zhe Guang, Michelle Rhodes, Rick Trebino, Georgia
Institute of Technology (United States)
In recent years, multi-mode fibers (MMFs) have drawn much attention.
In fiber communication, as conventional single-mode fiber transmission systems approach their capacity limit, researchers seek MMF solutions to increase the number of data channels. MMF-based sensors have been proposed for many applications because of their high sensitivity, easy fabrication, and low cost. They can measure physical quantities such as displacement, temperature, and refractive index using the interference between multiple fiber modes. MMFs have also been used for endoscopic imaging, waveform control through granular media, and fiber laser amplifications. Measuring modal contents of MMF output is therefore of great practical importance.
Although many approaches have been proposed, it is still difficult and inconvenient to completely measure MMF output. As MMF modes have different spatial shapes, propagation speeds (and hence arrival times), and spectral dispersion properties, the output pulse fields are generally spatiotemporally complex.
To completely characterize such complexities over space, time, and frequency, we use our recently developed pulse measurement technique
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STRIPED FISH. This device uses only a coarse grating, a bandpass filter, a couple of imaging optics, and a camera to capture the spatiotemporal field of MMF pulses, with no assumptions or scan needed. We demonstrate measured pulses from MMFs that support four linearly polarized modes
LP01, LP11, LP02 and LP21. And we show that a modal field analysis algorithm can decompose the measured field into orthogonal mode contents, making the measurement fast and easy. This approach characterizes fiber modes at different wavelengths, revealing their spatiotemporal structures due to propagation.
9740-17, Session 4
Daniel J . Kane, Mesa Photonics, LLC (United States); Nick
Hartmann, Ryan N . Coffee, Alan R . Fry, SLAC National
Accelerator Lab . (United States)
Ultrafast time dependent optical reflection and/or transmission spectroscopy can be used to measure time responses of materials, measure excitation pulse duration and/or relative arrival times between the excitation and optical probe pulses. A pump pulse, such as an ultrafast x-ray pulse, excites a material, changing its refractive index. The change of intensity of a reflected or transmitted optical probe pulse monitors the time dependent refractive index change. A helpful method for extracting temporal responses is to obtain a spectrogram of the transmission (or reflection) change by obtaining the optical intensity change versus time delay and wavelength.
The temporal response and the optical pulse can be extracted from the spectrogram using either blind- or cross-Frequency Resolved Optical Gating type deconvolutions. Transmission/reflection spectrograms can be obtained either using multishot or single-shot configurations. When large amounts of jitter between the excitation and probe pulses are present, as in the case of the Linac Coherent Light Source, single-shot configurations are preferred.
Because spectrograms are time-frequency entities, pulse and response intensity and phase is encoded into the intensity profile of the spectrogram.
Experimental artifacts such as artificial intensity variations created by optical beam inhomogeneity, inadvertent spectral variations, as well as anything else that can cause artificial intensity variations affect the retrieved material response and probe pulse. Under some circumstances, these problems are unavoidable. This paper will discuss retrieval artifacts caused by experimental issues as well as possible mitigation strategies.
9740-54, Session 4
Yves Bellouard, Ecole Polytechnique Fédérale de Lausanne
(Switzerland)
No Abstract Available
9740-57, Session 4
Conference 9740: Frontiers in Ultrafast Optics:
Biomedical, Scientific, and Industrial Applications XVI
Babu Varghese, Valentina Bonito, Simona Turco, Rieko
Verhagen, Philips Research (Netherlands) photothermolysis ranging from ablative to non-ablative, and more recently to fractional resurfacing differ in technology, efficacy of treatment, patient discomfort, side effects and social downtime. To overcome the limitations
Philips Research has developed a novel minimally invasive laser technology for skin rejuvenation using laser induced optical breakdown [1].
In this paper we experimentally demonstrate the influence of polarization and absorption on laser induced breakdown threshold in transparent, absorbing and scattering phantoms made from water suspensions of polystyrene microspheres. We demonstrate that radially polarized light yields a lower irradiance threshold for creating optical breakdown compared to linearly and circularly polarized light. We also demonstrate that the thermal initiation pathway used for generating seed electrons results in a lower irradiance threshold compared to multiphoton initiation pathway used for optical breakdown [2]. We experimentally demonstrate the transition from multiphoton initiation to thermal excitation and establish the optimal range of parameters required for creating breakdown at lower irradiance threshold using ns and ps pulses [3]. The results presented in this manuscript on the influence of polarization and absorption on the irradiance threshold for laser induced breakdown has potential applications in the fields of fundamental as well as applied research in obtaining desired photomechanical effects with lower irradiance. The lower intensity threshold obtained offers the benefits of creating deeper lesions inside the skin leading to precise and well-localized tissue effects with less risk of collateral damage, and thereby improving safety and efficacy of treatment
9740-18, Session 5
(Invited
Paper)
Yongfeng Lu, Wei Xiong, Ying Liu, Yunshen Zhou, Univ . of Nebraska-Lincoln (United States); Lan Jiang, Beijing
Institute of Technology (China); Tommaso Baldacchini,
Newport Corp . (United States); Jean-Francois Silvain,
Institut de Chimie de la Matière Condensée de Bordeaux
(France)
Additive nanofabrication by two-photon polymerization (TPP) has recently drawn increased attention due to its sub-100 nm resolution and truly three-dimensional (3D) structuring capability. Besides additive processes, subtractive process is also indispensable for various 3D fabrications. In modern 3D micro/nanofabrication, the combination of both additive and subtractive fabrication steps is not only desired but also demanded.
However, method possessing both additive and subtractive fabrication capabilities was rarely reported. Recently, we developed a complementary
3D micro/nanofabrication process by integrating both additive two-photon polymerization (TPP) and subtractive multi-photon ablation (MPA) into a single platform of femtosecond-laser direct writing process. Functional device structures were successfully fabricated including: polymer fiber
Bragg gratings containing periodic holes of 500-nm diameter and 3D micro-fluidic systems containing arrays of channels of 1µ m diameter. The integration of TPP and MPA processes enhances the micro/nanofabrication efficiency and enables the fabrication of complex 3D micro/nanostructures that are impractical to produce by either TPP or MPA alone. Doping of small molecules in polymers was used to promote TPP speed, spatial resolution, and mechanical strength. Doping of carbon nanotubes in polymers is possible to alter the electrical and mechanical properties of the fabricated structures. The new 3D micro/nanofabrication method is promising for a wide range of applications including integrated optics, metamaterials, microelectromechanical systems, and micro-fluidics.
The spectrum of laser based skin rejuvenation methods based on selective
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Conference 9740: Frontiers in Ultrafast Optics:
Biomedical, Scientific, and Industrial Applications XVI
9740-19, Session 5
Lauren L . Taylor, Rochester Institute of Technology (United
States); Jun Qiao, Rochester Institute of Technology
(United States) and Univ . of Science and Technology
Liaoning (China); Jie Qiao, Rochester Institute of
Technology (United States)
For the in-fiber polarizer based on low order mode LPFG, a polarization extinction ratio of more than 25 dB was observed at the wavelength of
1527.8 nm. A high order mode LPFG based in-fiber polarizer, with a broad bandwidth of 100 nm near 1550 nm, was investigated as well. The infiber polarization devices with low insertion loss may be useful in optical communications and fiber optic sensing applications.
9740-21, Session 5
Luis Andre Fernandes, Omur Sezerman, Garland Best, Mi
Li Ng, Saidou Kane, OZ Optics Ltd . (Canada)
Advanced fabrication and finishing techniques are desired for freeform optics and integrated photonics. Methods including grinding, polishing and magnetorheological finishing used for final figuring and polishing of such optics are time consuming, expensive, and may be unsuitable for complex surface features. Laser processing has been investigated as an alternative method for optic structuring, polishing, and welding, as direct tuning of laser parameters and flexible beam delivery are advantageous for complex freeform or photonics surfaces and material-specific processing. Continuous wave and pulsed laser radiation down to the nanosecond regime have been implemented to achieve nanoscale surface finishes through localized material melting, but the temporal extent of the laser-material interaction often results in the formation of a sub-surface heat affected zone. The temporal brevity of ultrafast laser radiation and the high intensities achieved at focus can allow for the direct vaporization of rough surface asperities with minimal melting, offering the potential for smooth, final surface quality with negligible heat affected material. We have experimentally tested the effectiveness of ultrafast laser radiation as an alternative laser source for processing silicon, silicon carbide, fused silica, and soda-lime glass. Simulation of material heating associated with ultrafast laser-material interaction has been performed and used to determine optimized, materialspecific processing parameters including laser fluence and scanning speed.
The parameter optimization process and results of experimental processing will be presented.
9740-20, Session 5
Lei Yuan, Baokai Cheng, Jie Liu, Clemson Univ . (United
States); Jie Huang, Missouri Univ . of Science and
Technology (United States); Hai Xiao, Clemson Univ .
(United States)
Femtosecond direct laser writing has recently shown great potential for the fabrication of complex integrated devices in the cladding of optical fibers. Such devices have the advantage of requiring no bulk optical components and no breaks in the fiber path, thus reducing the need for complicated alignment, eliminating contamination, and increasing stability.
This technology has already found applications using combinations of Bragg gratings, interferometers, and couplers for the fabrication of optical filters, sensors, and power monitors.
The femtosecond laser writing method produces a local modification of refractive index through non-linear absorption of the ultrafast laser pulses inside the dielectric material of both the core and cladding of the fiber.
However, fiber geometries that incorporate air or hollow structures, such as photonic crystal fibers (PCFs), still present a challenge since the index modification regions created by the writing process cannot be generated in the hollow regions of the fiber.
In this work, the femtosecond laser method is used together with a premodification method that consists of partially collapsing the hollow holes using an electrical arc discharge. The partial collapse of the photonic band gap structure provides a path for femtosecond laser written waveguides to couple light from the core to the edge of the fiber for in-line power monitoring. This novel approach is expected to have applications in other specialty fibers such as suspended core fibers and can open the way for the integration of complex devices and facilitate miniaturization of optical circuits to take advantage of the particular characteristics of the PCFs.
9740-22, Session 5
Johannes Gratt, Matthias Domke, FH Vorarlberg (Austria);
Ronald Sroka, Laser-Forschungslabor (Germany)
Control of the state of polarization (SOP) of light waves, especially in optical fibers, is essential in a variety of applications, such as optical communications, networking, spectroscopy, microscopy, and sensing.
However, the vast majority polarization controlling devices (e.g., wave plates and polarizers) used in existing fiber optic systems are still based on bulk-optic components. These bulk-optic devices have to be interfaced with optical fibers through collimators and pigtails. This not only increases the cost of implementation but also compromises the robustness of the system.
It is highly desired that the waveplates and polarizers can be implemented in an all-fiber form, preferably in a standard singlemode fiber, with minimum insertion loss and desirable performance.
This paper reports the stress-induced birefringence in an optical fiber by femtosecond laser (fs) irradiations and the fabrication of in-fiber waveplates and polarizers. Optical birefringence was created in a singlemode fiber by introducing a series of symmetric cuboid stress rods on both sides of the fiber core and along the fiber axis using fs irradiations. The stress-induced birefringence was estimated to be 2.42?10-4 at the optical wavelength of 1550 nm. By controlling the length of the stressed rods, waveplates of the desired polarization rotations can be fabricated. The stress-induced birefringence was further explored to fabricate in-fiber polarizers based on the polarization-dependent long-period fiber grating (LPFG) structure.
The photodynamic therapy or the laser-induced thermotherapy in the oncology and dermatology are two medical laser applications where a welldefined volume of tissue must be irradiated homogeneously over a length of up to several centimetres inside the human body. An optical fibre delivers the light into the human tissue. The challenge is to decouple the light at the fibre end. Polymer diffusors, which can be easily attached to the fibre tip, are limited regarding the desired laser power for therapy. A more promising approach is thus to directly modify the fibre end.
In this study a line of defects was ablated on the fibre’s surface using a femtosecond laser. These defects penetrate into the fibre core. In this way, the total internal reflection at the interface between core and cladding is inhibited and the light scatters at the roughened surface. The light scattering along the fibre and the transmission through the fibre was modelled as a function of the number, distance and size of defects using the Monte Carlo method. To verify the model, the transmission through the fibre was measured as a function of the number of defects with identical
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dimensions. Both, simulation and experiment, show that the decoupled output power first decreases linearly with the number of defects followed by an exponential decay according to Beer’s law. Finally, the simulation was used to find a strategy for calculating correct defect dimensions to fabricate a homogeneously emitting fibre diffusor with a length of several centimetres.
9740-23, Session 5
Conference 9740: Frontiers in Ultrafast Optics:
Biomedical, Scientific, and Industrial Applications XVI
Tao Yang, Yves Bellouard, Ecole Polytechnique Fédérale de
Lausanne (Switzerland) conventional OPOs. The scanning speed thus exceeds 10 nm/ms over a wide range from 650 nm to 1030 nm. Alternatively, rapid tuning between two or more defined wavelength is possible. This ultrafast wavelength selection or switching is also demonstrated.
A robust pump laser delivering 250 fs pulses at center wavelength of 515 nm with a pulse energy of > 100 nJ allows for a NOPO output power of up to
600 mW @ 50 MHz with a transform-limited pulse duration around 100 fs.
The concept is intrinsically scalable to higher energy or different wavelength regimes and first results on scalability will be presented. The tunable NOPO is therefore an ideal light source for novel ultrafast spectroscopy or twocolor imaging techniques.
Femtosecond laser-dielectric interaction in a three-dimensional (3D) manner defines a capable platform for integrated 3D micro-devices fabricated out of a single piece of system-material. Here, we add a new function to femtosecond laser-based single monolith in amorphous fused silica by demonstrating a transparent 3D micro-actuator using non-ablative femtosecond laser micromachining with subsequent chemical etching. The actuation principle is based on dielectrophoresis (DEP), defined as the unbalanced electrostatic action on dielectrics, due to an induced dipole moment under a non-uniform electric field. An analytical model of this actuation scheme is proposed, which is capable of performance prediction, design parameter optimization and motion instability analysis. Furthermore, the static and dynamic performances are experimentally characterized using optical measurement methods. An actuation range of 30 µ m is well attainable; resonances and the settling time in transient responses are measured; the quality factor and the bandwidth for the primary vertical resonance are also evaluated. Experimental results are in good consistence with theoretical analyses. The proposed actuation principle suppresses the need for electrodes on the mobile, non-conductive component and is particularly interesting for moving transparent elements. Thanks to the flexibility of femtosecond laser manufacturing process, this actuation scheme can be integrated in other functionalities within monolithic transparent Micro-Electro-Mechanical Systems (MEMS) for applications like resonators, adaptive lenses and integrated photonics circuits.
9740-25, Session 6
Brendan Reagan, XUV Lasers (United States) and
Colorado State Univ . (United States); Cory Baumgarten,
Michael Pedicone, Colorado State Univ . (United States);
Herman Bravo, XUV Lasers (United States); Liang Yin,
Colorado State Univ . (United States); Mark Woolston, XUV
Lasers (United States) and Colorado State Univ . (United
States); Hanchen Wang, Colorado State Univ . (United
States); Carmen S . Menoni, XUV Lasers (United States) and Colorado State Univ . (United States); Jorge Rocca,
Colorado State Univ . (United States) and XUV Lasers
(United States)
9740-24, Session 6
Thomas Binhammer, VENTEON Laser Technologies
GmbH (Germany); Yuliya Khanukaeva, Tino Lang,
Leibniz Univ . Hannover (Germany); Alex Pape, Laser
Quantum GmbH (Germany); Hauke Bensch, Leibniz
Univ . Hannover (Germany) and Laser Quantum GmbH
(Germany); Jan Ahrens, Oliver Prochnow, Laser Quantum
GmbH (Germany); Uwe Morgner, Leibniz Univ . Hannover
(Germany)
Our recent progress in the development of high energy / high average power, chirped pulse amplification laser systems based on diode-pumped
Yb:YAG amplifiers will be presented, including the demonstration of a laser that produces 1 Joule, sub-10 picosecond duration, ? = 1.03?m pulses at
500 Hz repetition rate. This compact, all-diode-pumped laser combines a mode-locked Yb:KYW oscillator and a water-cooled Yb:YAG preamplifer with two cryogenic power amplification stages to produce 1.5 Joule pulses with high beam quality which are subsequently compressed. This laser system, including pump lasers and optics and the in-vacuum dielectric grating pulse compressor, occupies an optical table area of less than 1.5x3 m^2. The high cooling-capacity cryogenic amplifier heads have a versatile modular design that allows the generation of a variety of pulse energies, repetition rates, and pulse durations depending on the application as well as scaling to higher peak and average power. This laser was employed to pump plasma-based soft x-ray lasers at ? = 10-20 nm at repetition rates >100
Hz. To accomplish this, temporally-shaped pulses were focused at grazing incidence into a high aspect ratio line focus using cylindrical optics on a high shot capacity rotating metal target. This results in an elongated plasma amplifier that produces microjoule pulses at several selectable and narrowlinewidth EUV wavelengths between ? = 109 Å and 189 Å. The resulting 0.2 mW average power in a transition of Ni-like molybdenum at 189 Å is the highest reported from a compact laser source these wavelengths.
We present a very fast tunable laser source which is based on a noncollinear optical parametrical oscillator (NOPO). Due to the ultrabroad gain bandwidth and an octave-spanning cavity design, very fast wavelength scans can be achieved which are intrinsically only limited by the cavity photon lifetime. This nearly instantaneous tuning or switching can be achieved, as there is no storage time in the gain material compared to a normal laser crystal. The concept of very broadband non-collinear phase matching which covers approx. 400 nm bandwidth and a careful dispersion management allows for a fast tunability of the center wavelength only by changing the cavity length. Since no angular or temperature tuning technique is required, the tuning speed is drastically increased compared to
9740-26, Session 6
Clemens Hönninger, Julien Pouysegur, Birgit Weichelt,
Martin Delaigue, Guillaume Machinet, Franck Morin, Florent
Guichard, Yoann Zaouter, Amplitude Systèmes (France);
Marc Hanna, Frédéric Druon, Patrick Georges, Lab . Charles
Fabry (France); Eric Mottay, Amplitude Systèmes (France)
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Conference 9740: Frontiers in Ultrafast Optics:
Biomedical, Scientific, and Industrial Applications XVI
Hybrid architectures based on the combination of fiber- and crystal-based building blocks are powerful configurations for the realization of high average power and high energy femtosecond lasers. These kind of laser architectures combine the advantages of both technologies: simplicity of integration and fabrication of fiber seeders and power and energy extraction capability of crystal-based booster amplifiers. The frontier between the two technologies can be floating and set on at different levels of average power and pulse energy, depending on the targeted requirements.
Several applications require high average power at the 100-W level at moderate pulse energies around 100 µ J and pulse repetition rates on the
MHz-level. Other applications require the same average power at higher energy levels in the mJ range and lower pulse repetition rates. Hybrid laser architectures are ideally suited to match to both requirements. In this paper, we present hybrid femtosecond lasers with pulse durations around 500 fs, average powers of 100 W, and pulse energies up to several mJ. Repetition rates reach from the 100-kHz-level to multi-MHz.
9740-29, Session 7
Klaus Bergner, Friedrich-Schiller-Univ . Jena (Germany);
Malte Kumkar, TRUMPF Laser- und Systemtechnik GmbH
(Germany); Andreas Tünnermann, Friedrich-Schiller-Univ .
Jena (Germany) and Fraunhofer-Institut für Angewandte
Optik und Feinmechanik (Germany); Stefan Nolte,
Friedrich-Schiller-Univ . Jena (Germany) and Fraunhofer-
Institut für Angewandte Optik und Feinmechanik
(Germany)
9740-27, Session 6
Max Kahmann, Raphael Gebs, Robert Fleischhaker, Ivo
Zawischa, Jochen Kleinbauer, Simone Russ, Lara Bauer,
Uwe Keller, Birgit Faisst, Aleksander Budnicki, Dirk Sutter,
TRUMPF GmbH & Co . KG (Germany)
The unique properties of ultrafast laser pulses with their low thermal influence pave the way to numerous novel applications. Particularly lasers in the sub-pico second regime, so called femtosecond lasers, achieved in the last decade an industrial ready reliability and regain an increasing recognition since these pulse durations combine the advantages of ultrashort pulses with higher efficiency especially for metals. However nowadays for some micro processing applications the infrared wavelength of these lasers is more and more a limiting factor. Thus the next generation of ultrafast industrial lasers have to enable the combination of the advantages of femtosecond pulses and shorter wavelength in order to enter the next stage in terms of precision as smaller focal spot size can be and better surface quality can be achieved. Further the higher photon energy of the shorter wavelength can open a low fluence regime for relevant applications in particular for metals, which is not accessible by infrared light, opening a wide range of opportunities.
I would like to participate in the student competition.
Ultrashort laser pulses offer several possibilities in glass processing, like induction of nanogratings or local welding. Another promising application is the inscription of disruptions, which can be used as cleaving layers in order to separate glass. Here, different spatial and temporal concepts are required to tailor the laser-matter dynamics. To this end it is necessary to understand the fundamental energy deposition and subsequent evolution of free carrier dynamics. The different decay channels lead to various modifications of the material.
Applying single laser shots with 1026nm wavelength, 6ps (FWHM) pulse duration and pulse energies from 25 µ J to 200 µ J leads to a plasma formation inside the glass species (fused silica, Borofloat 33, Gorilla glass).
We analyze the spatio-temporal evolution of free carriers induced by ultrashort laser pulses using a pump-probe setup with high temporal and spatial resolution.
The plasma development can be divided into 2 phases, a generation and a decay phase. Electron densities around 1 x 10^20cm-3 in the focal plane and
1 x 10^19cm-3 in front of the focus are generated. The free carriers slowly decay within several 100ps. However, the lower densities in front of the focus can be linked to fast electron heating and various decay stages, like exciton formation and self-trapping. These decay channels mainly lead to structural changes like bond breaking and generation of NBOHCs. On the other hand the high intensities inside the focus lead to a stronger electronphonon coupling resulting in strong disruptions.
9740-28, Session 7
(Invited
Paper)
François Courvoisier, Rémi Meyer, Ludovic Rapp, Ismail
Ouadghiri Idrissi, Remo Giust, Pierre-Ambroise Lacourt,
Luc Froehly, Luca Fufaro, Maxime Jacquot, John M . Dudley,
FEMTO-ST (France)
Bessel beams provide a novel route for ultrafast laser processing of solid dielectrics. This is because even at high intensity, they do not undergo nonlinear distortions and allow uniform energy deposition along the beam path. We will review benefits of Bessel -like beams for laser micro and nano-structuring of transparent materials with high aspect ratio: glass and sapphire cutting, high aspect ratio void formation. Of particular interest is the impact of the transverse beam shape and polarization on the control of stress and cracks in glass and sapphire, leading to cleavage after single pass illumination.
The research leading to these results, has received funding from the
European Union Seventh Framework Programme [ICT-2013.3.2- Photonics] under grant agreement n°619177, project TiSa-TD.
9740-30, Session 7
John Lopez, Univ . Bordeaux 1 (France)
Glass cutting is a subject of high interest for flat panel display and consumer electronics industries. Among laser-based, water jet-based and diamond tool-based existing solutions, ultrashort pulses (USP) appears as a promising technology since this laser technology has the unique capacity to produce highly localized bulk modification owing to non-linear absorption.
The cutting using USP lasers could be performed either by full ablation which is slow and generates a lot of dust, by controlled fracture propagation which is slow as well and may lead to path deviation, or by stealth dicing which produces rough sidewalls. The laser treatment is often continuous which is not necessary to perform glass cutting and may lead to overexposure.
In this paper we report on single pass glass and sapphire cutting using an
USP laser (20W @200kHz or 12W@2MHz), based on controlled fracture propagation or stealth dicing, using dash line laser treatment along the cutting trajectory. In-volume energy deposition was done along the glass thickness owing to a Gaussian or a Bessel beam. The results will be discussed in terms of sidewall profile and roughness, path deviation, rim sharpness, energy dose and feedrate. Dash line treatment enables to tune the energy deposition and to produce the cutting effect but with a narrower
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heat affected zone, a better sidewall quality and a more accurate trajectory control of the cutting path.
9740-31, Session 7
Conference 9740: Frontiers in Ultrafast Optics:
Biomedical, Scientific, and Industrial Applications XVI
Erden Ertorer, Ehsan Alimohammadian, Dale Gottlieb,
Jianzhao Li, Peter Herman, Univ . of Toronto (Canada)
9740-33, Session 7
Victor V . Matylitsky, Frank Hendricks, Spectra-Physics
(Austria)
Self-guiding of the beam created from laser pulses, which is also called filamentation, occurs as a consequence of the balance between selffocussing by the Kerr effect and defocusing in laser-generated plasma that arises when the high intensity also ionizes the material. By using this phenomenon, laser interaction can be extended over multiple Rayleigh lengths to enable high aspect ratio modifications with fast processing speeds. Other advantages of filament modification includes a small heat affected zone and minimal surface damage or crack generation.
Dimensions and the morphology of the filament modified zone are also highly dependent on laser parameters and focusing conditions. As a result of focusing and plasma defocusing cycles, ‘hot’ and ‘cold’ spots cause nonuniformities along the interaction zone with damaged zones alternating with gentle modification zones. Moreover, the energy consumed and deflected by the hot zones reduces the overall interaction length of the filament to yield low aspect ratio modification tracks.
In order to overcome these issues, a spatial light modulator (SLM) has been employed to actively rearrange the axial distribution of energy along the propagation axis. Laser filaments have been formed in bulk silica glasses with single and burst-train pulses of various energy from a femtosecond laser with 200 fs pulse duration and 515 nm wavelength. The SLM provided various focusing schemes such as forming multiple foci with controlled power splitting, introducing aberration, elongating the focus along the propagation direction, and forming a Bessel beam. Resulting filament tracks were investigated for their structural uniformity, length, and width and tuned by the SLM with optimized beam shaping to generate highly uniform structures variable from 10 um to 100s of um in length.
9740-32, Session 7
Patrick S . Salter, Bangshan Sun, Martin J . Booth, Univ . of
Oxford (United Kingdom)
Laser processing of optically transparent or semi-transparent, brittle materials is finding wide use in various manufacturing sectors. For example, in consumer electronic devices such as smartphones, e-readers, and tablets, cover glass needs to be cut precisely in various shapes. When an ultrashort laser pulse is focused inside glass, only the localized region in the neighborhood of the focal volume absorbs laser energy by nonlinear optical absorption. Therefore, the processing volume is strongly defined, while the rest of the target stays unaffected. Furthermore, only ultrashort pulse lasers allow cutting of the chemically strengthened substrates such as
XensationTM from Schott AG and Corning® Gorilla® glasses without cracking.
In this paper, we describe application of a femtosecond laser for machining of transparent materials by means of ablative and non-ablative laser processing. Ablation technologies will be compared with a newly developed non-ablative femtosecond process, ClearShapeTM, using the Spirit industrial femtosecond laser from Spectra-Physics. While ablative femtosecond processing provides the quality that industrial users demand, processing speed needs to be improved. An optimization method to determine the ideal laser processing parameters for multi-pass ablative material removal will be presented. Developed theoretical model helps to estimate the optimal kerf width and the number of scans in order to achieve the desired throughput. On the other hand, the ClearShape femtosecond process allows machining of transparent, brittle materials such as chemically strengthened glass, unstrengthened glass, and sapphire with highest quality and speed.
9740-34, Session 8
(Invited Paper)
Arnold Gillner, M . Jüngst, Patrick Gretzki, Martin
Reininghaus, Fraunhofer-Institute for Laser Technology
(Germany)
The focusing of ultrashort laser pulses is extremely important for various processes including multiphoton microscopy, photo-activation for biological studies, and laser fabrication. Adaptive optic elements, such as liquid crystal spatial light modulators or membrane deformable mirrors, are routinely used for the correction of aberrations in these systems, leading to improved resolution and efficiency. In this talk, we address the aspects of aberration correction specific to ultrashort pulses. We demonstrate with results from laser fabrication of transparent materials that adaptive elements used with ultrashort pulses may no longer be considered simply in terms of wavefront modification, but that changes to the incident intensity pulse front can also be important. We develop this principle further to show that a combination of adaptive elements, specifically a deformable mirror and spatial light modulator operated in concert, may be used to engineer pulse fronts
(contours of constant intensity in space and time within an ultrashort pulse).
By this approach, pulse fronts can be generated which are spatially variant across the beam. The simplest case is to generate a beam with a quadratic time delay in the pulse front from the centre to the edge of the beam.
This is an equivalent deformation to the propagation time delay (PTD) introduced to ultrashort pulses by many lenses. Experimental measurements of the temporal profile of a pulse in the expanded beam are backed up by observation of the two-photon fluorescence signal at the focus of an objective lens to illustrate the effect.
Ultra-short pulse lasers provide outstanding properties for high precision manufacturing with almost no thermal effects and numerous new micro and nano fabrication solutions [1]. With pulse durations in the picosecond and femtosecond range, the absorbed energy is concentrated in the material to a few nanometers, so that thermal damage to the materials can be avoided. These properties have generated numerous processes in precision machining at solar cells, batteries, injection molding tools and electronic components [2]. However for high speed processing and high productivity the used laser power has to be significantly increased. Currently ultrashort pulsed lasers with powers up to 500 W are available, so that also potential applications for macro processing are obtained, which opens large markets in other than the micro processing field [3]. However, using high power ultrashort pulsed lasers with high repetition rates in the MHz region can cause thermal issues like overheating, melt production and low ablation quality as long certain parameter sets and fluence ranges have been considered. High ablation quality only can be achieved, when the processing fluence is close to the ablation threshold, which requires new processing strategies and innovative system components. Beside ultra high speed scanning using polygon scanners the use of multiple laser beams provide the best and most versatile high power ablation solution. With switchable single beams using a special light modulator or a diffractive optical beam splitter, high ablation rates can be achieved while maintaining the high processing quality of ultra short pulse laser ablation. With this approach a next step up to an all optical manufacturing system can be provided.
[1] Du, K., Brüning, S., & Gillner, A,. High power picosecond laser with
400W average power for large scale applications. Paper presented at the
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Conference 9740: Frontiers in Ultrafast Optics:
Biomedical, Scientific, and Industrial Applications XVI
Proceedings of SPIE - the International Society for Optical Engineering,
8244, (2012)
[2] Gillner, A., Hartmann, C., & Dohrn, A., High quality micro machining with tailored short and ultra short laser pulses, 3rd Pacific International
Conference on Applications of Lasers and Optics, PICALO 2008 -
Conference Proceedings, 685-690. (2008)
[3] Russbueldt, P., Mans, T., Hoffmann, H. D., & Poprawe, R,. Status quo and outlook of power scaling of ultrafast lasers. 29th International Congress on Applications of Lasers and Electro-Optics, ICALEO 2010 - Congress
Proceedings, , 103 1226-1234, (2010).
9740-37, Session 8
(Invited Paper)
Wilhelm Pfleging, Peter Smyrek, Karlsruhe Institute of
Technology (Germany) and Karlsruhe Nano Micro Facility
(Germany); Melanie Mangang, Yijing Zheng, Karlsruhe
Institute of Technology (Germany); Johannes Pröll,
Karlsruhe Institute of Technology (Germany) and Karlsruhe
Nano Micro Facility (Germany)
9740-35, Session 8
Eric P . Mottay, Amélie Letan, Clemens Hönninger,
Amplitude Systèmes (France); Patrick Thibaut, Posalux SA
(Switzerland)
Optimizing the drilling process for injector fuel nozzles in automotive industry is one of the key factors to achieve significant improvements in fuel efficiency in the coming year. The quality of the nozzle holes edges, as well as careful optimization of the hole shape, allow to eventually optimise the fuel injection process in order to achieve the highest efficiency. The athermal and high quality nature of the ultrafast laser interaction process makes ultrafast laser drilling a prime candidate for this application. Several challenges need however to be overcome for industrial applications, such as processing speed, optimization of hole shape (zero-taper, inversedtaper, straightness …), as well as backwall protection. We will review in this presentation recent developments in ultrafast laser technologies, including advanced synchronisation modes and beam delivery system. Reducing the processing time requires improvement in laser average power, repetition rate, and operating mode. We will present hybrid ultrafast lasers, with the potential for simultaneously achieving high repetition rate, in the MHz regime, as well as high pulse energy. We will also present recent results obtained with non-normal incidence beams and trepanning heads. We will present examples of laser processing of Gasoline Direct Injectors.
Laser processes for cutting, modification and structuring of energy storage materials such as electrodes, separator materials and current collectors have a great potential in order to minimize the fabrication costs and to increase the performance and operational lifetime of high power lithiumion-batteries applicable for stand-alone electric energy storage devices and electric vehicles. Laser direct patterning of battery materials as well as laser-assisted formation of selforganized conical surface structures enable a rather new technical approach in order to adjust 3D surface architectures and porosity of composite electrode materials such as LiCoO2, LiMn2O4,
LiFePO4, Li(NiMnCo)O2, and Silicon. The architecture design, the increase of active surface area, and the porosity of electrodes or separator layers can be controlled by laser processes and it was shown that a huge impact on electrolyte wetting, lithium-ion diffusion kinetics, cell life-time and cycling stability can be achieved. In general ultrafast laser processing can be used for precise surface texturing of battery materials. Nevertheless, regarding cost-efficient production also nanosecond laser material processing can be successfully applied for selected types of energy storage materials. A concept for an advanced battery manufacturing including laser materials processing will be presented. For developing an optimized 3D architecture for high power composite thick film electrodes electrochemical analytics and post mortem analytics using laser-induced breakdown spectroscopy were performed. Based on mapping of the local state of charge of composite electrodes, an analytical approach for studying chemical degradation in structured and unstructured lithium-ion batteries will be presented.
9740-36, Session 8
Helena Kämmer, Felix Dreisow, Andreas Tünnermann,
Stefan Nolte, Friedrich-Schiller-Univ . Jena (Germany)
Ultrashort pulse laser processing is a precise technique for contact-free machining of microstructures with high quality and a negligible thermal effect in various materials, with many applications in research and industry, e.g. the drilling of fuel injection nozzles. Despite of many research activities the precise drilling of deep structures is still challenging. The hole shape in the depth is influenced by the previously excavated hole capillary, resulting in decreased drilling rates with increasing depth. Additionally the shape of the hole is not reproducible, even under identical conditions. In particular, the appearance of bulges, indentations, bendings and/or multiple capillaries with different orientations may vary statistically.
In this work, we analyze the use burst trains with pico- to nanosecond pulse separation in order to improve drilling efficiency and quality. Silicon serves as sample material for investigating the influence of laser drilling with 1030 nm bursts consisting of 200 fs pulses separated by a time delay between
1ps and 4ns. The deep drilling process is directly imaged from the side using a standard CCD camera and an illumination at 1064 nm, where the silicon sample is transparent. The results are compared to drilling without bursts for different pulse energies. The efficiency of the drilling process, the hole quality, as well as reproducibility of the hole shape are analyzed.
9740-38, Session 8
Martin Griebel, JENOPTIK Automatisierungstechnik GmbH
(Germany)
Ultrafast Lasers have been proven for several micro applications, e.g. stent cutting, for many years. Within its development of applications Jenoptik has started to use ultrafast lasers in macro applications in the automotive industry. The JenLas D2.fs-lasers with power output control via AOM is an ideal tool for closed loop controlled material processing. Jenoptik enhanced his well established sensor controlled laser weakening process for airbag covers to a new level. The patented process enables new materials using this kind of technology. One of the most sensitive cover materials is genuine leather. As a natural product it is extremely inhomogeneous and sensitive for any type of thermal load. The combination of femtosecond pulse ablation and closed loop control by multiple sensor array opens the door to a new quality level of defined weakening. Due to the fact, that the beam is directed by scanning equipment the process can be split in multiple cycles additionally reducing the local energy input. The development used the
5W model as well as the latest 10W release of JenLas D2.fs and achieved amazing processing speeds which directly fulfilled the requirements of the automotive industry. Having in mind that the average cycle time of automotive processes is about 60s, trials had been done of processing weakening lines in genuine leather of 1.2mm thickness. Parameters had been about 15 cycles with 300mm/s respectively resulting in an average speed of
20mm/s and a cycle time even below 60s. First samples had already given into functional and aging tests and passed successfully.
190 SPIE Photonics West 2016 · www.spie.org/pw
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9740-39, Session 8
Roland M . Mayerhofer, Jürgen Serbin, Fred-Walter Deeg,
Rofin-Baasel Lasertechnik GmbH & Co . KG (Germany)
Cold laser materials processing using ultra-short pulsed lasers has become one of the most promising new technologies for high-precision cutting, ablation, drilling and marking of almost all types of material, without causing excessive thermal damage to the part. These characteristics have opened up new application areas and materials for laser processing, allowing previously impossible features to be created and also reducing the amount of post-processing required to an absolute minimum, saving time and cost.
However, short pulse widths are only one part of the story for industrial manufacturing processes which focus on total costs and maximum productivity and production yield. Like every other production tool, ultrashort pulse lasers have to provide high quality results with maximum reliability. Robustness and global on-site support are vital factors, as well as easy system integration.
The presentation will give an overview on requirements on laser parameters derived from ultrafast laser material processing and conceptual options for ps- and fs-lasers. It will also discuss laser features and services turning USP lasers into industrial solutions.
9740-40, Session 9
Conference 9740: Frontiers in Ultrafast Optics:
Biomedical, Scientific, and Industrial Applications XVI
Feinmechanik (Germany)
Eric Audouard, Eric P . Mottay, Amplitude Systèmes
(France)
In this work, we report on the laser ablation of silicon samples using bursts of 200fs pulses at a wavelength of 1030nm. Two different experimental approaches were used to generate bursts starting with the pristine laser pulses at a repetition rate of 60 kHz. A Michelson interferometer-based set-up enabled the generation of bursts with time separation between subpulses from 510ps to 4080ps, while a different set-up consisting of an array of birefringent crystals allowed shorter separations in the range from 0.5ps to 16ps.
The ablation thresholds and craters depth achieved with the burst-mode processing have been measured and compared to results obtained with the unsplit pristine pulses of equivalent total fluence. It was found that while the ablation threshold is reduced with increasing number of sub-pulses, irrespective of the time delay within the burst, the ablation depth per sub-pulse as a function of the laser fluence exhibits a different behavior depending on the time separation between sub-pulses. For sub-pulse delays shorter than 4ps, for a given burst energy, the crater becomes shallower the larger the number of sub-pulses in the burst is. In contrast, for time separations longer than 510ps, the ablation depth increases with the number of pulses in the bursts. This different behavior can be ascribed to a change of the laser radiation effective penetration depth.
9740-42, Session 10
Matthias Domke, Bernadette Egle, FH Vorarlberg (Austria);
Gernot Fasching, Marius Bodea, Elisabeth Schwarz,
Infineon Technologies Austria AG (Austria)
We present a simple engineering model to reproduce and predict laser processing with ultrafast pulses. We aim at reaching a good estimate of porcessing parameters in various technical situations (static or dynamic beams, single or multi-pulses). The modes does not investigate the influence of specific laser-matter interaction mechanisms, for instance electonc and lattice temperature evolution. Assuming a non linear ligarithmic response of the materials to ultrafast pulses, each material can be described by two global parameters. As the response to a Gaussian shaped pulse is an hyperbolic shaped crater, analytical results are derived. Typical ablation data evolution with fluence such as crater depth and volume ablation rate repoduces experimental results on a wide range of fluences. Effects of top-hat and gaussian profiles can be compared. Optimal fluences for various processes are presented. Dynamical processing is considered, taking into account pulse response superpostion. Simple technical assumptions allow to predict the effet of beam velocity and non normal incident beams and to obtain key parameters for laser processing, such as conical shapes or processing time. In particular, we apply the model to percussion and trepanning drilling with non normal incident beams.
High power electronic chips are fabricated on 50 µ m thin Si wafers to improve heat dissipation. At these chip thicknesses mechanical dicing becomes challenging. Chippings may occur at the cutting edges that reduce the mechanical stability of the die. Thermal load changes could then lead to sudden chip failure. A promising tool to improve the cutting quality are ultrashort pulsed lasers, because thermal side effects can be reduced to a minimum.
However, ultrashort pulse laser scribing of Si leads to the formation of periodic holes – also called cone-like protrusions (CLP) - at the trench bottom. These CLPs turn into furrows with a period and depth of about 1 µ m at the lower cutting edge, if a thin wafer is cut fully. The goal of this study is to investigate the influence of these defects on the backside breaking strength of the die.
For this purpose, an ultrafast laser with a pulse duration of 380 fs was operated at pulse frequency of 200 kHz to cut a wafer into 2.89x3.6 mm? small chips. Wavelength (1040 nm and 520 nm), pulse energy, polarization, scan speed and number of scans was varied. The breaking strength was evaluated using the 3 point bending test. The cutting edges were investigated using confocal microscopy and scanning electron microscopy.
The results indicate that the morphology of the defects at the lower cutting edge influences the backside breaking strength. Moreover, the bending test results show that ultrashort pulse laser dicing improves the breaking strength compared to mechanical dicing.
9740-41, Session 9
Caterina Gaudiuso, Univ . degli Studi di Bari Aldo Moro
(Italy) and Istituto di Fotonica e Nanotecnologie (Italy);
Helena Kämmer, Felix Dreisow, Friedrich-Schiller-Univ .
Jena (Germany); Antonio Ancona, CNR-Istituto di
Fotonica e Nanotecnologie (Italy); Andreas Tünnermann,
Stefan Nolte, Friedrich-Schiller-Univ . Jena (Germany) and Fraunhofer-Institut für Angewandte Optik und
9740-43, Session 11
Javier Hernandez Rueda, Univ . of California, Davis (United
States); Jasper Clarijs, Univ . of California, Davis (United
States) and Utrecht Univ . (Netherlands); Jan Siegel, Javier
Solis, Instituto de Óptica “Daza de Valdés” (Spain) and
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Conference 9740: Frontiers in Ultrafast Optics:
Biomedical, Scientific, and Industrial Applications XVI
Consejo Superior de Investigaciones Científicas (Spain);
Hao Zhang, Dries van Oosten, Utrecht Univ . (Netherlands);
Denise M . Krol, Univ . of California, Davis (United States)
Surface ablation of fused silica using single ultrashort laser pulses has been investigated. It is well-known that when an intense fs-laser pulse is focused at the surface of a dielectric its photons may locally ionize the material via non-linear absorption, giving rise to free charge carriers. In the presence of these excited electrons the local dielectric function changes dynamically, as the carrier density rises under the influence of laser photons and decays in its absence. Hence, the optical properties of the material change as the laser pulse impinges on the material surface. We have experimentally and theoretically investigated this complex physical problem from both a static and a dynamical perspective.
The theoretical model, used in this work, is based on finite difference time domain (FDTD) method and allows for calculating the self-reflectivity and the temporally resolved surface reflectivity of a dielectric irradiated using fs-laser pulses. We couple the FDTD simulation to a single rate equation that describes the carrier density (driven by multiphoton ionization, avalanche ionization and recombination). Using this carrier density, the transient dielectric constant used in the FDTD simulation (Drude plus Kerr terms included) is dynamically updated.
On the experimental side, we have captured images of the pump-beam that is back reflected (self-reflectivity) from the interface and studied the change in reflectivity due to laser-plasma interaction during single shot irradiation of glass. Furthermore, the e--plasma dynamics has been measured using fsmicroscopy, where the transient reflectivity was imaged for several temporal delays using a probe-beam. We discuss the effect of the temporal shape of the laser pulse on the laser energy coupling and its influence on the final surface topography.
9740-44, Session 11
Frank Hendricks, Victor V . Matylitsky, Spectra-Physics
(Austria); Matthias Domke, FH Vorarlberg (Austria); Heinz
P . Huber, Munich Univ . of Applied Sciences (Germany)
Laser processing of optically transparent or semi-transparent, brittle materials is finding wide use in various manufacturing sectors. For example, in consumer electronic devices such as smartphones or tablets, cover glass needs to be cut precisely in various shapes. The unique advantage of material processing with femtosecond lasers is efficient, fast and localized energy deposition in nearly all types of solid materials. When an ultrashort laser pulse is focused inside glass, only the localized region in the neighborhood of the focal volume absorbs laser energy by nonlinear optical absorption. Therefore, the processing volume is strongly defined, while the rest of the target stays unaffected. Thus ultrashort pulse lasers allow cutting of the chemically strengthened glasses such as Corning® Gorilla® glass without cracking.
Non-ablative cutting of transparent, brittle materials, using the newly developed femtosecond process ClearShapeTM from Spectra-Physics®, is based on producing a micron-sized material modification track with well-defined geometry inside. The key point for further improvement of the process is to understand the induced modification by a single femtosecond laser shot. In this paper, pump-probe microscopy techniques have been applied to study the defect formation inside of transparent materials on a time scale between one nanosecond to several tens of microseconds.
The observed effects include pressure and rarefaction wave propagation as well as mechanical stress formation in the bulk of the glass. Besides better understanding of underlying physical mechanisms, our experimental observations have helped us to find optimal process parameters for the glass cutting application and lead to better quality and speed for the
ClearShapeTM process.
9740-45, Session 12
(Invited Paper)
Alexandre Mermillod-Blondin, Benjamin Klessen, Federico
J . A . Furch, Marc J . J . Vrakking, Max-Born-Institut für
Nichtlineare Optik und Kurzzeitspektroskopie (Germany)
Laser pulse duration is a factor of paramount importance when considering direct laser bulk microprocessing of transparent materials in tight focusing conditions (NA ~ 0.5). Regardless of the chemical composition of the substrate, the existence of two laser-matter interaction types (Type I and
Type II) is firmly established [1].
In fused silica, Type I modifications can only be obtained when using a pulse duration below 180 fs and modest pulse energies (0.1 to 0.2 ?J). The shorter the pulse duration, the wider the processing window. For instance, microprocessing with a 40-fs pulse duration results in Type I modifications for pulse energies up to 0.4 ?J.[2]
Type I microstructures are characterized by a uniform, smooth refractive index higher than the refractive index of the pristine bulk. Besides, Type I microstructures are produced with no collateral damage (such as cracks or stress around the irradiated region). This combination offers a unique potential for applications such as low-stress laser marking or direct laser writing of photonic structures in thin samples.
Our most recent results demonstrate that using few-cycle pulses (pulse duration < 10 fs) enables producing Type I modifications over an extended microprocessing window. The few-cycle laser source [3] is a non-collinear optical parametric amplifier (NOPA) delivering sub-7 fs laser pulses at a repetition rate of 400 kHz with a pulse energy of ~ 10 ?J. The laser pulses are focused with high numerical aperture (0.5), all-reflective optics in the bulk of pure fused silica samples.
We study the influence of the irradiation conditions (pulse energy, number of pulses, numerical aperture of the focusing system) on the characteristics of the laser-induced microstructures. The characterization of the photoinduced microstructures (morphology, refractive index change) is performed with a spatial light interference microscopy apparatus. [4]
References:
[1]: Gross et al., “On the use of the Type I and II scheme for classifying ultrafast laser direct-write photonics” Opt. Express, 23, pp. 7767-7770,
(2015).
[2]: Taylor et al., “Applications of femtosecond laser induced self-organized planar nanocracks inside fused silica glass” Laser Photon. Rev., 2, pp. 26-46,
(2008).
[3]: Furch et al., “Improved characteristics of high repetition rate noncollinear optical parametric amplifiers for electron ion-coincidence spectroscopy” Conference on Laser and Electro-Optics, San Jose, CA, paper
SF1M.5 (May 2015).
[4]: Wang et al., “Spatial light interference microscopy (SLIM)” Opt. Express
19, 1016-1026, (2011).
9740-46, Session 12
Thomas Winkler, Univ . Kassel (Germany); Lasse Haahr-
Lillevang, Aarhus Univ . (Denmark); Cristian Sarpe-Tudoran,
Nadine Götte, Bastian Zielinski, Nikolai Jelzow, Arne
Senftleben, Thomas Baumert, Univ . Kassel (Germany)
192 SPIE Photonics West 2016 · www.spie.org/pw
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Conference 9740: Frontiers in Ultrafast Optics:
Biomedical, Scientific, and Industrial Applications XVI
The generation of a free electron plasma is the first step in the laser ablation of high bandgap materials. We have demonstrated that tailored ultrashort laser pulses are suitable for robust manipulation of optical breakdown, increasing the precision of ablation to one order of magnitude below the optical diffraction limit [1]. In this work, laser excitation of dielectrics under ambient conditions is investigated by temporally- and radially-resolved common-path spectral interferometry [2,3]. Besides water, fused silica and sapphire are excited by ultrashort bandwidth-limited and temporally asymmetric shaped femtosecond laser pulses, where the latter start with an intense main pulse followed by a decaying pulse sequence. Spectral interference in an imaging geometry allows measurements of the transient optical properties integrated along the propagation through the sample but radially-resolved with respect to the transverse beam profile. Since the optical properties reflect the dynamics of the free-electron plasma, such measurements reveal the spatial characteristics of the laser excitation.
Furthermore, post mortem analysis of ablation structures corresponding to the spectral-interference measurements were performed. We conclude, by comparing the experiments with rate equation simulations, that temporally asymmetric shaped laser pulses are a promising tool for high-precision laser material processing, as they reduce the transverse area of excitation, but increase the excitation inside the material along the beam propagation.
[1] L. Englert et al., Opt. Expr. 15, 17855 (2007); JLA 24, 042002 (2012)
[2] C. Sarpe et al., NJP 14, 075021 (2012)
[3] T. Winkler et al., Appl. Surf. Sci., submitted 06/2015
9740-48, Session 12
Christos E . Athanasiou, Yves Bellouard, Ecole
Polytechnique Fédérale de Lausanne (Switzerland)
Due to its unique mechanical, optical and chemical properties fused silica is commonly used in a variety of applications, from optics to biotechnologies and more recently, as a platform of integrated microsystems combining fluidics, optics and mechanics. At the micro- and nano- scale, amorphous silica exhibits unconventional behaviour. More generally, the micromechanics of silica, as well as its polymorphic phases, remain largely unexplored due to the inherent experimental challenges associated with mechanical testing of micron-size specimens. Recently, we reported on the use of a monolithic microscale tensile tester, fabricated by a femtosecond laser, to measure fused silica’s micromechanical properties.
The use of this instrument can be diversified for the investigation of the mechanical properties of silica’s laser-induced composite structures. Here, we will present first results on the mechanical properties of laser affected zones as well as stress relaxation phenomena of femtosecond-laser affected zones.
9740-47, Session 12
Javier Hernandez Rueda, Univ . of California, Davis (United
States); Dries van Oosten, Utrecht Univ . (Netherlands);
Jonathan J . Witcher, Univ . of California, Davis (United
States); Jasper Clarijs, Univ . of California, Davis (United
States) and Utrecht Univ . (Netherlands); Denise M . Krol,
Univ . of California, Davis (United States)
We have studied the dynamics and the spectral dependence of the transient optical properties inside zinc aluminium phosphate glasses and fused silica under conditions of femtosecond (fs) laser waveguide fabrication. We have made use of a fs-resolved pump and probe arrangement, which allows for measuring the transient optical transmission at different wavelengths. Such experimental system has two operation modes, where either spatial (at a particular wavelength) or spectral resolution can be achieved along with temporal resolution.
Transient transmission spectroscopy and microscopy together with a simple Drude-like physical model were used for inferring the maximum electron density achieved for bulk processing using tightly focused fslaser pulses. This quantitative method can be utilized for predicting the bounds where smooth or explosive processes occur inside the material. In addition, it allows us to understand the influence of processing parameters of paramount importance, such as pulse duration, polarization state or laser wavelength, on the underlying physical mechanisms. Ultimately, the acquired knowledge from the processing dynamics can be applied for improving the performance of laser-inscribed optical waveguides, i.e. reduce transmission losses or enhance refractive index contrast.
In addition to temporally resolved measurements, the use of spatially resolved spectroscopy during waveguide writing was found to be a reliable indicator of the smoothness of the final optical modification. Therefore, such spectral signature, in terms of the central wavelength of the emitted spectrum, was also utilized for optimization of the inscribed waveguides.
9740-49, Session PTue
Javier Hernandez Rueda, Jasper Clarijs, Univ . of California,
Davis (United States); Charmayne E . Smith, Richard K .
Brow, Missouri Univ . of Science and Technology (United
States); Denise M . Krol, Univ . of California, Davis (United
States)
We have investigated the permanent refractive index changes inside fused silica and zinc phosphate glasses after laser inscription of waveguides using ultrashort laser pulses at different wavelengths. The aim of this work is to elucidate the relationship between the laser wavelength and the materials structural changes linked to smooth optical modification. To this end the laser frequency was detuned using an optical parametric amplifier (OPA) combined with a confocal arrangement (for cleaning the laser spatial profile). Afterwards, for laser direct writing a microscope objective (10x,
NA = 0.24) was used for focusing the beam inside a glass sample, which was translated along the laser propagation axis by means of a motorized translation stage.
The laser-induced structural changes were measured using Raman spectroscopy both for tracks of damage and for good optical waveguides.
The structural changes were inferred from peak shifts and relative intensity fluctuations associated with representative Raman bands. In the case of fused silica changes in the 605 cm-1 peak, which is due to 3-membered
Si-O ring structures, were monitored while in the case of phosphate glass we focused on the 1209 cm-1 peak, which is linked to Q2-like tetrahedra.
The suitability for waveguiding and the refractive index changes were respectively inspected by measuring the near and far field output profiles using a continuous wave laser at 660 nm. Since the photon energy rules the order of the multiphoton absorption in dielectrics, the role of the laser wavelength for waveguide fabrication will be discussed in terms of the influence of the ionization mechanisms on the laser energy coupling and the maximum electron density obtained.
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Conference 9740: Frontiers in Ultrafast Optics:
Biomedical, Scientific, and Industrial Applications XVI
9740-50, Session PTue
Masayuki Kakehata, Hidehiko Yashiro, National Institute of Advanced Industrial Science and Technology (Japan);
Ayako Oyane, Nanosystem Research Institute (Japan) and National Institute of Advanced Industrial Science and Technology (Japan); Atsuo Ito, Health Research Ctr .,
AIST (Japan); Kenji Torizuka, Electronics and Photonics
Research Institute (Japan) and National Institute of
Advanced Industrial Science and Technology (Japan) or negative refractive index changes did not allow demonstrating guiding for other compositions. The laser-induced structural changes within the glass network were studied by means of spatially resolved micro Raman and fluorescence spectroscopy. While slight or no peak shifts, of relevant
Raman bands, were found, a strong fluorescence signal was measured and associated with POHC electronic defect formation. These results and corresponding changes of optical properties are discussed in relation with the O/P atomic ratios favorable for waveguide fabrication.
9740-52, Session PTue
Christopher Martin, Murat Yildirim, Adela Ben-Yakar, The
Univ . of Texas at Austin (United States)
The 3-mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP), which is one of fine engineering ceramics, offers advantages in application for mechanical components and medical implants due to its high resistance to fracture and flexural strength. The control of surface roughness improves the character of the device in some applications. The laser-induced periodic surface structures (LIPSS) by ultrashort pulse lasers have never been investigated for 3Y-TZP in detail. In this paper, the formation and characteristics of LIPSS formed on 3Y-TZP are reported especially focused on the pulsewidth dependence which shows unique dependence.
A laboratory made Ti:sapphire chirped-pulse amplification system, which generates 810nm-centered 80-fs pulses at 570Hz repetition rate, was employed. The 3Y-TZP samples, of which surface were wet-polished to mirror quality, were made from a fine powder (TZ-3YB-E, Tosoh) with sintering temperature at 1350 ºC. The measured ablation threshold peak fluence was ~1.5 J/cm2 and the LIPSS was formed for the peak fluence of 2.7
~7.7 J/cm2. The lines of the LIPSS was parallel to the direction of the linearly polarized light and the period of LIPSS was comparable or larger than the center wavelength of the laser.
The dependence of LIPSS on pulsewidth was investigated by changing the dispersion of the pulses. The period of the LIPSS clearly increased
(~860nm-1100nm) with increasing the pulsewidth (80fs - 500fs), while no dependence on the sign of the chirp was observed. These new characteristics are discussed by comparing with the LIPSS for different materials reported.
Ultrafast pulsed lasers are a promising tool for precise and noninvasive tissue surgery. The high peak intensity of the pulses allows nonlinear interaction with tissue, causing three-dimensional confined ablation without thermal damage thanks to low pulse energies. However, deep tissue ablation has been limited to a few scattering lengths due to laser beam extinction. As pulse energies are increased to overcome attenuation, unwanted side effects can occur such as surface ablation and self-focusing, where the highly intense pulse alters the refractive index of the material, causing a lensing effect and long filaments of damage before the focus.
Here, we examine the optimal laser parameters to overcome extinction and self-focusing for deep tissue ablation. Through histological images, we show that changing the pulse width from the typically used 100-200 femtosecond range to 1-2 picoseconds delays the onset of self-focusing because of the decreased power during the pulse; the pulse energy required to hit the critical power for self-focusing is increased without a corresponding increase in the pulse energy required for ablation. Additionally, we simulate the maximum ablation depth for pulses of different wavelengths, and show that wavelengths of ~1.5 microns can ablate deeply because of reduced scattering in tissue and an increase in the critical power requirement for selffocusing. We discuss other potential solutions to increase ablation depth, including temporal focusing.
9740-51, Session PTue
Nikolay Skovorodnikov, Javier Hernandez Rueda, Vladimir
A . Semenov, Denise M . Krol, Univ . of California, Davis
(United States)
Femtosecond (fs) pulsed laser inscription was used to fabricate optical waveguides in ternary zinc magnesium phosphate glasses with different compositions. The main goal of this work was to find a reliable dielectric material for fs-laser waveguide writing, which has particular physical properties. The material is to be mechanically robust and chemically durable and is to exhibit positive refractive index change under fs-laser irradiation.
Besides, such phosphate glass structures possess an advantageous high solubility of rare-earth ions, which can be potentially exploited for the fabrication of active photonic devices.
In order to produce optical changes a fs-laser beam was focused inside the material so a sufficient intensity was reached and permanent structural modification could be induced at the focal volume. The glass samples were translated along the laser beam direction; therefore elongated optical modifications were formed. Whether the written lines were able to guide light was verified by measuring the near-field profile of the output mode of the waveguide at 660 nm. This way, optical guiding was demonstrated for the sample 25MgO 25ZnO 50P2O5 (mole %). Either tracks of damage
9740-53, Session PTue
Sergey S . Golik, Alexey A . Ilyin, Tamara M . Agapova,
Michael Y . Babiy, Yuliya S . Biryukova, Alexander Y . Mayor,
Nataliya N . Golik, Far Eastern Federal Univ . (Russian
Federation)
The time-resolved femtosecond laser-induced breakdown spectroscopy
(LIBS) was used to analyze human hairs and nails. Spitfire Ti:sapphire amplifier system (Spectra-Physics) was used as a source of femtosecond laser pulses (<45 fs, pulse energy up to 5 mJ) and ICCD cameras (PicoStar
HR, LaVision and PI-MAX3, Princeton Instruments) coupled with 2500i or
2300 Acton SpectraPro spectrographs were used as a detectors. Plasma was generated by focusing laser radiation directly on the nail surface or on the glued strand of hairs. Gate delays were varied from 0 to 200 ns and kinetic of luminescence of emission lines and background spectra were obtained in spectral range of 200-750 nm. Measurements of three age groups (18-29,
30-49, 50+ ages) of different social classes were carried out. The numbers of the chemical elements emission lines were determined and their ratio by age groups was compared. Correlation between concentrations of elements
(Na, Ca, K, Mg) in hairs and nails was obtained. It is shown that femtosecond
LIBS can be a promising technique for the analysis of essential and toxic elements in hair and nails and allows to diagnose disorders of mineral metabolism in the human body.
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Conference 9740: Frontiers in Ultrafast Optics:
Biomedical, Scientific, and Industrial Applications XVI
9740-55, Session PTue
Kazumasa Ariyasu, Mitsuhiro Terakawa, Keio Univ . (Japan)
In this study, rupture of biodegradable polymer capsules containing fluorescent molecules after femtosecond laser irradiation was investigated.
Biodegradable polymer capsules containing FITC-dextran were fabricated with emulsification method using coaxial dual-nozzle. The average diameter of the fabricated capsules was 22.5±0.8 ?m. The capsules were suspended into distilled water in a glass-bottom dish followed by the irradiation of near-infrared femtosecond laser pulses from the top side.
After laser irradiation, residual capsules were observed by using phasecontrast microscope to evaluate the residual ratio of capsules. The ratio decreased with increasing laser fluence. These results suggest the rupture of biodegradable polymer capsules triggered by the laser irradiation.
Surface morphologies of the residual capsules were observed with scanning electron microscope. Melted-like structures were found on the surface of the capsules. These results indicate the possibility of changing degradation speed which affects the drug releasing properties by femtosecond laser irradiation.
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9741-1, Session 1
Anna Möhl, Sven Wickenhagen, Ulrike Fuchs, asphericon
GmbH (Germany)
Many laser applications, especially in the field of material processing, lithography or optical data storage, require a uniform intensity distribution, rather than the well known Gaussian beam profile of the working beam to guarantee an optimum performance. To generate such a top-hat beam profile several approaches are already known. One of the most promising strategies is to use refractive optical elements because they are very efficient, have a simple structure, are easier to manufacture compared to diffractive solutions and are more flexible with respect to wavelength changes. Several theoretical designs for refractive beam shaping systems have already been developed and published. But for the practical application of these systems it is of major interest to know the desired manufacturing specifications to fabricate the particular elements so that an appropriate quality of the top-hat beam profile can be achieved.
In the scope of this paper two different systems consisting of aspheric lenses are described, which efficiently transform a collimated Gaussian beam to a collimated top-hat beam. Both systems are of the Galilean telescope type. The design principles are discussed and the as-built performance is analyzed and compared quantitatively with the theoretical design. For this different criteria to evaluate the quality of the top-hat beam profile are defined. Additionally the effects of deviations from the actual optical design conditions such as wavelength, input beam profile, working distance etc. are considered for the as-built system. Consequently valuable statements on the manufacturing requirements of the aspheric lenses can be made.
9741-2, Session 2
Max C . Funck, Björn Wedel, Sebastian Eilzer, PT Photonic
Tools GmbH (Germany)
We present a modular fiber beam delivery system for micromachining applications with industrial pico- and femtosecond lasers. Comprising beam launching unit, laser light cable as well as collimation and focusing units, the system is flexibly integrated into existing applications. Micro-structured hollow core fibers inside the sealed laser light cable efficiently guide highpower laser pulses over distances of several meters with excellent beam quality, while power, pulse duration and polarization are maintained. We report on robust and stable beam transport during dynamic operation as in robot or gantry systems and will discuss application to different laser sources together with optional pulse compression.
9741-4, Session 2
Carlo Holly, RWTH Aachen Univ . (Germany); Martin
Traub, Hans-Dieter Hoffmann, Fraunhofer-Institut für
Lasertechnik (Germany); Claudia Widmann, Dietmar Brink,
Christoph Nebel, Fraunhofer-Institut für Angewandte
Festkörperphysik (Germany); Titus Gotthardt, Muharrem
Ceyhun Sözbir, Christian Wenzel, Fraunhofer-Institut für
Produktionstechnologie (Germany)
The potential of diamond as an optical material for high-power laser applications in the wavelength regime from VIS to NIR is investigated.
Monocrystalline diamonds with lateral dimensions up to 7 x 7 mm? are grown with microwave-plasma assisted chemical vapor deposition
(CVD) in parallel with up to 60 substrates and are further processed to spherical optics for beam guidance and shaping. The synthetic diamonds offer superior thermal, mechanical and optical properties, including low birefringence, scattering and absorption, also around 1 µ m wavelength.
We present dielectric (AR and HR) coated monocrystalline diamond optics which are tested under high laser power in the multi-kW regime. The thermally induced focal shift of the diamond substrates is compared to the focal shift of a standard collimating and focusing unit for laser cutting made of fused silica optics. Due to the high thermal conductivity and low absorption of the diamond substrates compared to the fused silica optics no additional focal shift caused by a thermally induced refractive index change in the diamond is observed in our experiments. We present experimental results regarding the performance of the diamond substrates with and without dielectric coatings under high power and the influences of growth induced birefringence on the optical quality. Finally, we discuss the potential of the presented diamond lenses for high-power applications in the field of laser materials processing.
9741-5, Session 2
Annika Völl, RWTH Aachen Univ . (Germany); Jochen
Stollenwerk, RWTH Aachen Univ . (Germany) and
Fraunhofer-Institut für Lasertechnik (Germany); Peter
Loosen, Fraunhofer-Institut für Lasertechnik (Germany) and RWTH Aachen Univ (Germany)
Laser beam intensity distribution profiles for material processing techniques are most of the time restricted to be either of Gaussian or tophat shape.
This often leads to different kind of problems especially at the edges of the laser-heated tracks, examples are energy losses or unnecessary overlaps.
Thus, machining quality and process efficiency could be much improved by using application specific intensity profiles to generate optimal temperature distributions in the processed material. In this work, we present a numerical method to derive a specific intensity profile for a given temperature distribution. As this problem belongs to the set of inverse heat conduction problems, which are ill-posed, special regularization algorithms are needed.
The only method to solve this inverse problem in reasonable time is the conjugate gradient method which we extend to the given problem of laser material processing applications. This method is an iterative approach where in each step the actual temperature distribution is calculated by using the finite element method. In general, the proposed method is applicable for materials with constant or temperature dependent coefficients, for static and dynamic distributions as well as for plane or complex geometries.
However, restricting ourselves to plane geometries, intensity distributions that create tophat- or stepped temperature distributions on the plane surface of the processed material are derived and will be presented. In future work, we intend to verify these results using freeform optics as well as singly addressable V(E)CSEL arrays.
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Conference 9741: High-Power Laser Materials Processing:
Lasers, Beam Delivery, Diagnostics, and Applications V
9741-28, Session PTue
Benjamin Lempe, Tobias Baselt, Peter Hartmann,
Westsächsische Hochschule Zwickau (Germany) and
Fraunhofer IWS Dresden (Germany) for improvement.
In this paper, we report on the latest developments in multi-pulse drilling using an IPG QCW fibre laser. The latter delivers at a tuneable repetition rate (from single shot up to 2 kHz), laser pulses whose width is adjustable in between 0.20-10 ms with peak power up to 12 kW. We have focused our work on drilling of thick sheets of steel alloys with different geometries
(diameter, angular orientation) and different processing strategies (static, on the fly, pulse trains). We will show that using such laser system it is possible to decrease the processing time while limiting the heat affected zones and collateral effects. Finally, the impact on the geometry of the holes of the different physical processes in play during the drilling will be discussed.
Online process control systems often only detect the temperature at a local area of the machining point and determine an integrated value. In order to determine the proper welding quality and the absence of defects such as temperature-induced stress cracks it is necessary to do time- and spaceresolved measurements before, during and after the production process.
The system under development consists of a beam splitting unit which divides the electromagnetic radiation of the heated component on two different sensor types. For high temperatures, a sensor is used which is sensitive in the visible spectrum and has a dynamic range of 120dB. Thus, very high intensity differences can be displayed and a direct analysis of the temperature profile of the weld spots is possible. A second sensor is operating in the wavelength range from 1 micron to 5 microns and allows the determination of temperatures from approximately 200°C. At the beginning of a welding process, the heat-up phase of the metal is critical to the resultant weld quality. If a defined temperature range exceeded too fast, the risk of cracking is significantly increased. During the welding process the thermal supervision of the central processing location is decisive for a high secure weld. In the border areas as well as in connection of the welding process especially cooling processes are crucial for the homogeneity of the results. In order to obtain sufficiently accurate resolution of the dynamic heating- and cooling-processes, the system can carry out up to 500 frames per second.
9741-8, Session 3
Markus Bohrer, Dr . Bohrer Lasertec GmbH (Austria)
Laser engraving is used since decades as a well-established process e.g. for the production of print and embossing forms for many goods in daily life as e.g. decorating cans and printing bank notes. Yet it is a more or less socalled fire and forget process.
From the original artists plan to the digitization and then especially from the laser source itself with electronic signals, the RF, the plasma discharge regarding CO2 lasers to the behavior of the optical beam delivery - especially if an AOM is used - to the interaction of the laser beam with the material itself - it is long process chain.
The most resent results using CO2 lasers with AOMs and the research with a scanning electron microscope (SEM) and a confocal laser scanning microscope (CLSM) as a set of correlative microscopy to evaluate the high speed engraving characteristics is presented in this paper.
9741-6, Session 3
(Invited
Paper)
Arnold Gillner, Fraunhofer-Institut für Lasertechnik
(Germany)
No Abstract Available
9741-7, Session 3
Minh NGuyen, LOMA, UMR 5798 (France); Charlie loumena, Rainer Kling, ALPhANOV (France); Cyrille
Delor, Turbomeca (France); Eric Freysz, LOMA, UMR 5798
(France)
Processing of helicopter engines faster, better and more reliably is the triptych which binds LOMA, ALPHANOV and TURBOMECA. In current production machines, flash lamp pumped lasers are employed to drill thousands of cooling holes with specific geometries and diameters to ensure a homogeneous air flow over the surface. However the repeatability of the process does not satisfy the criteria of quality inspection. Therefore, the three partners started an initiative to identify and overcome the shortcomings of the current process, where the laser source is a key element
9741-9, Session 3
Sebastian Pricking, Petra Welp, Raphael Gebs, Robert
Fleischhaker, Jochen Kleinbauer, Aleksander Budnicki, Dirk
H . Sutter, Alexander Killi, TRUMPF Laser GmbH (Germany);
Michael Mielke, TRUMPF Inc . (United States)
We report on an industrial fiber-based laser system delivering ultrashort pulses in the range of a few picoseconds down to a few hundred femtoseconds with high average power suitable for high-precision micromachining. The used hollow-core photonic crystal fibers exhibit a Kagomé lattice and a hypocycloid core wall enabling the delivery of the laser radiation over several meters with exceptionally low losses and preservation of the high beam quality of M2 better than 1.3. The modematching and coupling optics are integrated into the laser head providing a compact footprint without the need for external boxes. The laser head is carefully designed regarding its thermo-mechanical properties to allow a highly reliable coupling stability. The exchangeable delivery fiber is packaged using our well established LLK-D connectors which offer a very high mechanical precision, the possibility to add water cooling, as well as full featured safety functions. The fiber is hermetically sealed and protected by a robust but flexible hose providing bend protection and break detection.
We show the optical linear and nonlinear properties of the transported laser radiation and discuss its feasibility for pulse compression. The measurements are supported by the simulation of the pulse propagation by solving the nonlinear Schrödinger equation implementing the splitstep Fourier method. In addition, the mode properties are measured and
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Conference 9741: High-Power Laser Materials Processing:
Lasers, Beam Delivery, Diagnostics, and Applications V confirmed by finite element method simulations. The presented industrial laser system therefore expands the known advantages of ultra-short pulses with the flexibility of fiber delivery yielding a versatile tool perfectly suitable for all kinds of micromachining applications.
significantly. Therefore, the simulation model is used to analyse the effect of laser beam direction, beam profile and beam oscillations on the energy input, the process temperatures and the seam formation..
9741-29, Session 3
Kazeem O Sanusi, Stephen Akinlabi, Esther T Akinlabi,
Univ . of Johannesburg (South Africa)
Laser Beam Forming (LBF) process is an emerging and new forming method that generally requires brute force to forge the steel into the desired shape instead of using conventional methods. This study investigates the changes that occur in low carbon steel through the laser beam forming process. The parameters under investigation include variable scanning speed and number of scans at fixed laser intensity. The effect of these laser parameters on the chemical composition and microstructure of low carbon steel is assessed through characterisation of both the as received and LBF specimens. Characterization of the laser formed steels were studied using microstructural analysis, micro hardness profiling and tensile test measurements. The effects of the laser parameters on the material properties of the laser beam formed steels were then determined. Dry sliding tests were also conducted to compare the wear behavior of the
LBF samples. The results show that there is a significant increase in the mechanical and wear properties of the Laser Beam Formed materials. The results obtained will contribute towards the further optimization of laser forming methods for steel for the optimization of the mechanical properties of steel.
9741-10, Session 4
Michael Dobler, Lehrstuhl für Photonische Technologien
(Germany) and Erlangen Graduate School in Advanced
Optical Technologies (Germany); Philipp Wiethop, Daniel
Schmid, AUDI AG (Germany); Michael Schmidt, Lehrstuhl für Photonische Technologien (Germany) and Erlangen
Graduate School in Advanced Optical Technologies
(Germany)
Laser beam brazing is a well-established joining technology in car body manufacturing with main applications in the joining of divided tail gates and the joining of roof and side panels. A key advantage of laser brazed joints is that the seams satisfy highest visual quality requirements. However, the laser beam brazing process is very complex and process dynamics is only partially understood.
In order to gain deeper knowledge of the laser beam brazing process and to determine optimal process parameters, a transient three-dimensional simulation model of laser beam brazing is developed. Recently, the fluid dynamics sub-model has been extended by taking into account marangoni convection, buoyancy effects and dynamic wetting phenomena.
The Verification of the individual sub-models for heat transfer and fluid flow demonstrates the capabilities of the implemented numerical models.
A Validation of the simulation model is performed by metallographic analysis and thermo couple measurements for different parameter sets of the brazing process. These results show that the multi-physical simulation model not only can be used to gain insight into the dynamics of the laser brazing process but also offers the possibility for process optimization in industrial applications.
Small deviations in the energy input can affect the brazing results
9741-11, Session 4
Christian Hennigs, Rabi Lahdo, André Springer, Stefan
Kaierle, Michael Hustedt, Laser Zentrum Hannover e .V .
(Germany); Helmut Brand, Richard Wloka, Frank Zobel,
Peter Dültgen, Institut für Werkzeugforschung und
Werkstoffe (Germany)
To process natural stone such as marble or granite, saw blades equipped with wear-resistant diamond cutting segments are used, typically joined to the blade by brazing. In case of damage or wear, they must be exchanged.
Due to the large energy input during thermal loosening and subsequent brazing, the repair causes extended heat-affected zones with serious microstructure changes, resulting in shape distortions and disadvantageous stress distributions. Consequently, axial run-out deviations and cutting losses increase.
In this work, a new near-infrared laser-based process chain is presented to overcome the deficits of conventional brazing-based repair. Ideally, additional tensioning and straightening steps can be avoided. The process chain starts with roughening and activation of the relevant joining surfaces, using short-pulsed laser radiation. Afterwards, the cutting segments are glued onto the blade using continuous-wave laser radiation. Here, the onecomponent epoxy resin is heated to its curing temperature by irradiating the respective cutting segment, ensuring minimal thermal influence on the blade. The third step is the thermal loosening of worn segments, using a continuous-wave laser to heat the segment gently and to exceed the resin’s decomposition temperature. Finally, short-pulsed laser radiation removes remaining resin from the blade in order to achieve clean joining surfaces.
For demonstration, a prototype unit was constructed to perform the different steps of the process chain on-site at the saw-blade user’s facilities.
This unit was used to re-equip a saw blade with a complete set of cutting segments. This saw blade was used successfully to cut different materials, amongst others granite.
9741-12, Session 4
Nathalie F . Timpe, Julia Stuch, Marcus Scholl, Ulrich A .
Russek, Rheinische Fachhochschule Köln (Germany)
This contribution presents a phenomenological, analytical model for laser welding of polymers which is suited for a quick process quality estimation for the practitioner. Besides material properties of the polymer and processing parameters like welding pressure, feed rate and laser power the model is based on a simple few parameter description of the size and shape of the laser power density distribution (PDD) in the processing zone. The model allows an estimation of the weld seam tensile strength. It is based on energy balance considerations within a thin sheet with the thickness of the optical penetration depth on the surface of the absorbing welding partner.
The joining process itself is modelled by a phenomenological approach.
The model reproduces the experimentally known process windows for the main process parameters correctly. Using the parameters describing the shape of the laser PDD the critical dependence of the process windows
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on the PDD shape will be demonstrated. The tensile strength of weldings performed with different PDD shapes will be predicted and compared with experiments. The adaption of the model to other laser manufacturing processes where the PDD influence can be modelled comparably will be discussed.
9741-13, Session 4
Conference 9741: High-Power Laser Materials Processing:
Lasers, Beam Delivery, Diagnostics, and Applications V
Mutiu F . Erinosho, Esther T . Akinlabi, Univ . of Johannesburg
(South Africa)
Titanium alloys (Ti6Al4V) Grade 5 have been regarded as the most useful alloys for the aerospace applications, due to their light weight properties.
Today, laser technology is an energetic process in which the beam ejected can travel a longer distance and spot on the focused surface.
The combination of metallic powder and laser beam has been used concurrently to form a solid figure. However, this combination has generated a permanently solidified adhesive bonding between the laser-deposited metallic powders. Several research works have been conducted to improve the mechanical properties of the primary alloy. This article conversely highlights the series of work that have been conducted on improving the mechanical properties and microstructures of the primary alloy with the addition of titanium carbide (TiC). The Ti-6Al-4V alloy has been widely selected in most critical part of a component. Their reinforcement with TiC composite particle has been achieved successfully through the optimal usage of laser technology. The characteristics of the reinforced component have vehemently improved the mechanical properties such as the tensile strength, wear resistance, fracture toughness and hardness; as well as the morphologies and phases of the microstructures.
9741-14, Session 5
Peter Stritt, Daniel Weller, Rudolf Weber, Thomas Graf,
Univ . Stuttgart (Germany) power in the few-millisecond range at a wavelength of 515 nm with a duty cycle of 10%. Careful shaping and stabilization of the polarization and spectral properties lead to an optical-to-optical efficiency higher than 55%.
The beam parameter product is designed and measured to be below 5 mm mrad which allows the transport by a fiber with a 100 µ m core diameter.
The fiber and beam guidance optics are adapted to the green wavelength, enabling low transmission losses and stable operation. Application tests show that this laser is perfectly suited for copper welding due to the superior absorption of the green wavelength compared to IR, which allows us to produce weld spots with an unprecedented reproducibility in diameter and welding depth. With an optimized set of parameters we could achieve a splatter-free welding process of copper, which is crucial for welding electronic components. Furthermore, the surface condition does not influence the welding process when the green wavelength is used, which allows to skip any expensive preprocessing steps like tin-coating.
With minor changes we could operate the laser in cw mode and achieved up to 1.7 kW of cw power at 515 nm with a beam parameter product of 2.5 mm mrad. These parameters make the laser perfectly suitable for additional applications such as selective laser melting of copper.
9741-16, Session 5
Philipp von Witzendorff, Stefan Kaierle, Oliver Suttmann,
Laser Zentrum Hannover e .V . (Germany); Ludger
Overmeyer, Leibniz Univ . Hannover (Germany)
Pulsed laser sources with pulse durations in the millisecond regime can be used for spot welding and seam welding of aluminum. Seam welds are generally produced with several overlapping spot welds. Hot cracking has its origin in the solidification process of individual spot welds which determines the cracking morphology along the seam welding. This study used a monitoring unit to capture the crack geometry within individual spot welds during seam welding to investigate the conditions for initiation, propagation and healing (re-melting) of solidification cracking within overlapping pulsed laser welds. The results suggest that small crack radii and high crack angles with respect to welding direction are favorable conditions for crack healing.
Optimized pulse shapes were used to produce butt welds of 0.5 mm thick
6082 aluminum alloys. Tensile tests were performed to investigate the mechanical strength in the as-welded condition.
Close edge laser welding of high strength 6000series aluminum alloy is known to cause centerline hot cracks. Those cracks result from the thermomechanical strain and stress conditions when welding close to the sheet edge. A numerical finite element model has been developed to quantify the mechanical strain and define a criterion for the hot crack sensitivity. Thus appropriate strategies preventing centerline cracks can be derived. The presented strategies reduce the resultant strain during solidification and will be used for validation of the numerical model.
9741-15, Session 5
Sebastian Pricking, Rudolf Huber, Konrad Klausmann, Elke
Kaiser, Christian Stolzenburg, Alexander Killi, TRUMPF
Laser GmbH (Germany)
We report on industrial high-power lasers in the green wavelength regime.
By means of a thin disk oscillator and a resonator-internal nonlinear crystal for second harmonic generation we are able to extract up to 8 kW pulse
9741-17, Session 5
Stephanie Miller, Erik Pfeif, Andrei Kazakov, Esther
Baumann, Marla Dowell, National Institute of Standards and Technology (United States)
Welding and joining of components is a necessary process for modern manufacturing processes throughout the world. Laser welding has been shown to be effective for joining similar and dissimilar materials including metal to plastic and metal to ceramic bonding. However, due to a lack of understanding of laser-material interactions, laser welding remains an underutilized joining technology. In an effort to augment and elucidate laser-material interactions, NIST has undertaken an integrative initiative between the physical measurements laboratory and the materials measurement laboratory to benefit the advanced laser manufacturing environment.
This study will focus on a small portion of the work conducted at NIST,
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which includes the preliminary results of the characterization of similar and dissimilar fiber laser welding of automotive steel sheet. Preliminary parameter development, hardness profiles, and microstructural characterization for butt and lap joints of dual phase steels joined to austenitic and ferritic steel will be presented. Additionally, a comparison of light optical profilometry and Light Detection And Ranging (LiDAR) for potential in-line profilometry will be presented.
9741-18, Session 5
Conference 9741: High-Power Laser Materials Processing:
Lasers, Beam Delivery, Diagnostics, and Applications V
Andreas Ganser, Stefan Liebl, Patrick Schmitz, Michael F .
Zäh, Technische Univ . München (Germany)
9741-19, Session 6
Paul A . Williams, Brian J . Simonds, Jeffrey Sowards,
Joshua Hadler, National Institute of Standards and
Technology (United States)
The advantages of laser beam welding, such as its high flexibility, its high local en-ergy input, and its fast processing speed, led to a substantial increase of industrial applications of the technology. However, only a portion of the laser energy is ab-sorbed during welding due to reflections.
These reflections can damage the system components and lead to a reduced process efficiency. Especially when welding copper materials with infrared laser beam sources the reflections play an important role, since the reflection coefficient of copper is high at infrared wavelengths. There-fore, a formation of a keyhole is necessary for a stable and efficient welding process.
A theoretical model for the calculation of the reflections on an arbitrary position above the process zone is presented, as well as a radiation analyzer with a modular setup. This device enables a time- and space-resolved measurement of the reflected radiation. Using the experimental results, characteristic positions on the hemisphere could be identified to calibrate the theoretical model. The calibrated model enables to analyze the reflected energy during the welding process and to determine the en-ergy which is absorbed by the work piece.
In laser manufacturing operations, accurate measurement of laser power is important for product quality, operational repeatability, and process validation. Accurate real-time measurement of high-power lasers, however, is difficult. Typical thermal power meters must absorb all the laser power in order to measure it. This forces power meters to be large, slow and exclusive
(that is, the laser cannot be used for its intended purpose during the measurement). To address these limitations, we have developed a different paradigm in laser power measurement where the power is not measured according to its thermal equivalent but rather by measuring its momentum
(radiation pressure). Very simply, light reflecting from a mirror imparts a small force perpendicular to the mirror which is proportional to the optical power. By mounting a high-reflectivity mirror on a high-sensitivity force transducer (scale), we are able to measure laser power in the range of tens of Watts up to ~ 100 kW. The critical parameters for such a device are mirror reflectivity, angle of incidence, and scale sensitivity.
We will describe our experimental characterization of a radiation-pressurebased optical power meter. We have tested it for modulated and CW laser powers up to 92 kW in the laboratory and up to 20 kW in an experimental laser welding booth. We will describe current accuracy, temporal response, sources of measurement uncertainty, and hurdles which must be overcome to have an accurate power meter capable of routine operation as a turning mirror within a laser delivery head.
9741-30, Session 5
Christian Hoff, Kevin Cromwell, Jörg Hermsdorf, Laser
Zentrum Hannover e .V . (Germany); Meriem Akin, Marc
C . Wurz, Leibniz Univ . Hannover (Germany); Stefan
Kaierle, Ludger Overmeyer, Laser Zentrum Hannover e .V .
(Germany)
Polymers with low glass transition temperatures are flexible materials and often serve as an optical waveguide or as substrates for the layer structure in applications such as in humidity- or temperature sensors. The aim of the presented work is to develop a laser-based method to connect conducting paths with suitable electrical and mechanical properties without stressing the substrate thermo-mechanically. By the use of the transmission laser bonding of low melting eutectic alloys the necessary energy can be introduced very precisely and processing times can be reduced. In this work,
52In48Sn and 66In34Bi 3D dummy components are successfully joined on rigid substrates. Experimental results will be presented which illustrate the mechanical stability of these compounds.
9741-20, Session 6
Julia Stuch, Nathalie F . Timpe, Marcus Scholl, Ulrich A .
Russek, Rheinische Fachhochschule Köln (Germany)
This work is motivated by the observation that the shape of a laser power density distribution (PDD) significantly influences the manufacturing quality in numerous laser processes. Lacking appropriate PDD shape parameters these influence, however, is not described quantitatively by few characteristic figures of the PDD. The paper presents a new quantitative, application adapted few parameter characterisation of the PDD shape. For nearly circular PDDs the localisation as just one additional parameter on top of the common characteristics beam power and PDD radius is introduced and proven as meaningful. The localisation is based on the fourth moment of the PDD. This ensures simple optical transformation properties and thus easy adjustability of the localisation of the laser beam as manufacturing tool. Together with beam power and radius the localisation allows to determine the power fractions in the central and a ringlike outer region of the PDD as well as the fraction outside the PDD radius. This will be shown by application of rating functions which assess the spatial regions of the PDD with different weights. Applications to real beams used for laser manufacturing will be demonstrated. For the examples of surface dominated laser processes it will be shown briefly that this approximate shape description with one additional parameter allows an estimate of
PDD influence on manufacturing quality. An outlook on further shape characterising parameters is given.
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Conference 9741: High-Power Laser Materials Processing:
Lasers, Beam Delivery, Diagnostics, and Applications V
9741-21, Session 6
Jed A . Simmons, Jeffrey L . Guttman, John McCauley,
Ophir-Spiricon, LLC (United States)
High power lasers in excess of 1 kW generate enough Rayleigh scatter, even in the NIR, to be detected by silicon based sensor arrays. A lens and camera system in an off-axis position can therefore be used as a non-contact diagnostic tool for high power lasers. Despite the simplicity of the concept, technical challenges have been encountered in the development of an instrument referred to as BeamWatch. These technical challenges include reducing background radiation, achieving high signal to noise ratio, reducing saturation events caused by particulates crossing the beam, correcting images to achieve accurate beam width measurements, creating algorithms for the removal of non-uniformities, and creating two simultaneous views of the beam from orthogonal directions. Background radiation in the image was reduced by the proper positioning of the back plane and the placement of absorbing materials on the internal surfaces of BeamWatch. Maximizing signal to noise ratio, important to the real-time monitoring of focus position, was aided by increasing lens throughput. The number of particulates crossing the beam path was reduced by creating a positive pressure inside
BeamWatch. Image correction was performed on each row using a line spread function deconvolution. Algorithms in the software removed nonuniformities in the data prior to generating waist width, divergence, BPP, and M2 results. A dual axis version of BeamWatch was developed by the use of mirrors. By its nature BeamWatch produced results similar to scanning slit measurements. Scanning slit data was therefore taken and compared favorably with BeamWatch results.
9741-23, Session 6
Nicholas J . Harrop, Reinhard Kramer, Otto Maerten, Stefan
Wolf, PRIMES GmbH (Germany)
Modern high brilliance near infrared lasers have seen a tremendous growth in applications throughout the world. Increased productivity has been achieved by higher laser power and increased brilliance of lasers. Positive impacts on the performance and costs of parts are opposed to threats on process stability and quality, namely shift of focus position over time. A high initial process quality will be reduced by contamination of optics, eventually leading to a focus shift or even destruction of the optics.
Focus analysis at full power of multikilowatt high brilliance lasers is a very demanding task because of high power densities in the spot and the high power load on optical elements. With the newly developed high power projection optics, the HighPower-MicroSpotMonitor-HighBrilliance (HP-
MSM-HB) is able to measure focus diameter as low as 20 µ m at power levels up to 10 kW at very low internal focus shift.
A main driving factor behind thermally induced focus shift is the absorption level of the optical element. A newly developed measuring system is designed to determine the relative absorption level in reference to a gold standard. Test results presented show a direct correlation between absorption levels and focus shift.
The ability to determine the absorption level of optical elements as well as their performance at full processing power before they are put to use, enables a high level of quality assurance for optics manufacturers and processing head manufacturers alike.
9741-22, Session 6
Jie Qiao, Rochester Institute of Technology (United States) and Aktiwave LLC (United States); Aaron Schweinsberg,
Univ . of Rochester (United States); Zachary Mulhollan,
Mathieu Chalifour, Rochester Institute of Technology
(United States); Christophe Dorrer, Aktiwave LLC (United
States)
Wavefront sensing is important to many fields such as astronomy for atmospheric turbulence, and characterization of aberrations present in optical systems and the human eye. The optical differentiation wavefront sensor (ODWS) uses a gradient transmission filter in the far field of the wave under test to measure the wavefront slopes from intensity measurements made at the observation plane. This sensor has the potential to achieve higher spatial resolution, higher wavefront slope dynamic range, and lower cost when compared to the conventional Shack-Hartmann wavefront sensor.
An ODWS system allows for the detection of finer features in a wavefront’s curvature, which could prove to be invaluable for freeform optics metrology.
In this work we describe the setup and testing of an ODWS, made using a binary pixelated mask. We also construct a numerical model of the ODWS to measure the signal to noise ratio of the system, as well as examine the robustness of wavefront reconstruction in regards to tolerancing of key system components and focal spot size incident on the transmission filter.
We demonstrate the accuracy and consistency of the ODWS by performing several self-consistency checks, comparing its measurements to the output of the numerical model and those of a commercial Shack-Hartmann sensor.
By introducing a deformable mirror into the input plane, we are able to generate custom wavefronts that enable us to measure the sensitivity and spatial resolution of the ODWS and compare its performance to the Shack-
Hartmann. We also test the performance of the ODWS under broadband illumination.
9741-24, Session 7
(Invited
Paper)
Peter Stritt, Meiko Boley, Andreas Heider, Institut für
Strahlwerkzeuge (Germany); Florian Fetzer, Michael
Jarwitz, Daniel Weller, Institut für Strahlwerkzeuge
(Germany); Rudolf Weber, Institut für Strahlwerkzeuge
(Germany); Peter Berger, Institut für Strahlwerkzeuge
(Germany); Thomas Graf, Institut für Strahlwerkzeuge
(Germany)
Fundamental process monitoring is very helpful to understand the complex interactions during the capillary welding process to prevent weld defects.
Various studies on monitoring of laser welding processes of aluminum, copper and steel were performed. Coaxial analyses in real-time with inline coherent imaging and photodiode based measurements have been applied as well as off-axis thermography, spectroscopy, online X-Ray observation and high-speed imaging with 808?nm illumination wavelength. The presented diagnostic and monitoring methods were appropriate to study typical weld defects like pores, spatters and cracks. Using these diagnostics allowed understanding the formation of such defects and developing strategies to prevent them.
9741-25, Session 7
Markus Kogel-Hollacher, Martin Schoenleber, Precitec
Optronik GmbH (Germany)
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+1 360 676 3290 · help@spie.org 201

With respect to in-process measurements in laser materials processing there still are unsolved tasks, e.g. the on-line measurement of the depth of a keyhole generated by a high power laser beam or the topography measurement of laser structured parts structured. Since the first time a keyhole was generated with lasers there is a need to quantify this value
“penetration depth” while processing. With the IDM system (In-Process
Depth Meter) it is now possible to bring a system to market, which can measure the depth of the keyhole in industrial laser welding applications.
Besides the measurement of the depth of the vapor capillary for laser welding applications, now allowing to keep the welding depth with an accuracy of micrometers and a sub millisecond temporal resolution or even closed-loop control it, further use of the technology includes the acquisition of 3D images around the laser process itself, allowing for coaxial integration of pre- and post-process sensors.
Besides all the effort in mechanical and optical integration of the sensor components, the real innovation with the adapted technology is as follows; the accuracy of the interferometric measurement is not affected by electromagnetic emissions from the vapor capillary or their adjacent areas, neither in deep penetration welding nor during laser surface modification.
Only the “own” light emitted from low coherent light sources leads to interference between the reference and the measurement path. Thus with accurate positioning of the measuring point, a measurement of the depth of the keyhole is possible coaxially to the processing laser regardless of weld geometry and material. The only limitation is the dimension of the measurement point relative to the spot size of the laser processing and the size of the measurement range in the axial direction
9741-26, Session 7
Conference 9741: High-Power Laser Materials Processing:
Lasers, Beam Delivery, Diagnostics, and Applications V
Ulrich Thombansen, Peter Abels, Fraunhofer-Institut für
Lasertechnik (Germany)
9741-27, Session 7
Biswajit Pathak, Bosanta R . Boruah, Indian Institute of
Technology Guwahati (India)
Reduced estimation time in zonal wavefront sensing can play a very important role in many application areas such as adaptive optics, in the characterization of a quickly varying wavefront phase profile and so on. In a Shack-Hartmann wavefront sensor (SHWS) the detector or the recording medium of a SHWS is the sole constraint of temporal resolution. This is because the required number of rows of the detector array is an integral multiple of the number of rows of the lenslet array, thus putting a limit on the faster detector array frame rate achievable. Using computer generated holography technique, the array of lenslets in the SHWS can be substituted by an array of binary diffraction grating pattern followed by a focusing lens. The transmittance functions of each of the grating element can be configured to produce a 1D array of focal spots of a desired order whose positions can be used to estimate the local slope information in a way similar to the SHWS. On the other hand, to capture 1D array the number of effective rows required in the digital camera is less which leads to a very high frame rate of wavefront sensing. In this paper, we show that the formation of 1D array of focal spots further facilitates in the process of single indexed wavefront estimation that considerably reduces the wavefront estimation time compared to a two index addressing of the slope information. Here, we will present preliminary experimental results to make a comparison of the wavefront estimation time required between the usual double indexing and single indexing, associated with the 2D and 1D array of focal spots respectively.
Melting of metal powder by laser radiation is moving to a broad variety of manufacturing businesses. This move is accompanied by several providers of machines that offer a professional handling of materials and a sound design of the process. However, the path from the planned course of the process towards the achieved material properties is still not fully described.
The report discusses the different approaches of time resolved pyrometric detection of thermal emission, acquisition of spatially resolved images of the melt pool as well as spectrally resolved monitoring of the process’ emission.
It does so by acquiring data with a system that provides a technical solution that enables the acquisition of all information synchronously. Pyrometric signals are acquired at 100 kHz, thermal imaging with 500Hz and spectral monitoring in the kilohertz range. In addition, this system provides a full alignment of all that data to the position of origin. The analyses identify correlations between the signal sources to enable the analysis of simplified systems based on knowledge about the process behaviour. This increases the understanding and interpretation of events that occur at the same time in multiple sources. The findings will provide an orientation for future implementation of monitoring systems.
202 SPIE Photonics West 2016 · www.spie.org/pw
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