Photon Physics
with Jefferson Lab’s Free-Electron Laser
Michelle Shinn
May 30, 2013
Jefferson Lab User’s Group Meeting
Newport News, VA
This work was supported by U.S. DOE Contract No. DE-AC05-84-ER40150, the
Commonwealth of Virginia, Air Force Office of Scientific Research, DOE Basic Energy
Sciences, the Office of Naval Research, and the Joint Technology Office.
Outline
• An introduction to Free-Electron Lasers (FELs)
– What makes the JLab FELs unique?
• Exploring the nature of matter with the FEL
– Applications in the THz, IR, UV, & VUV
• Conclusions
The Jefferson Lab Site & Free Electron Laser Facility
The Free-electron laser (FEL)
History of the FELs at JLab
• 1989 Two JLab scientists propose using SRF linac technology to drive an
FEL.
• 1991 Hermann Grunder the first Director, recruits hires two scientists to,
among other things, build the case for an FEL at JLab.
• 1994 A team is assembled to create and submit a PDR to the DOE to
build an FEL that would operate in the UV for industry and science.
• 1995 May - the PDR “Free Electron Lasers for Industry”, for $27M, was
submitted to DOE.
• Proposed demonstration of energy recovery at high currents
• Identified applications included: antimicrobial nylon
– Micro-machined metals, ceramics,…
– Processing electronics materials
Energy recovery enables high average power FELs
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Since the amount of power removed from the beam is small the majority of the
beam power is available after the lasing interaction.
Most facilities dump that beam.
– Creates a lot of induced radioactivity
We set the pathlength such that the electrons re-entering the cryomodule are
180°in phase with the accelerated bunches.
The used electrons decelerate and their energy is given back to the RF field in
the cavities.
– Electrons are dumped at their original injected energy (< 10 MeV)
– No induced radioactivity
This raises the overall efficiency of FELs, e.g.,
– We only have enough RF power to accelerate 1 mA of beam.
• But operationally, our current limit is that from the photogun’s DC
power supply (10 mA in our case).
– Efficiency improves as the ratio of the beam energy to injection energy.
Existing JLab IR/UV Light Source
E = 135 MeV present limit
Up to135 pC pulses @ 75 MHz
20 μJ/pulse in (250)–700 nm UV-VIS
120 μJ/pulse in 1-10 μm IR
1 μJ/pulse in THz
VUV Light to
Lab 1
The first high current ERL
14 kW average power
Ultra-fast (150 fs)
Ultra-bright
CW Performance
wavelength (µm)
cw (kW)
1.1 1.6
2.2 14.6
2.8
6.7
6.0
8.5
JLab FEL Facility Performance
ULS
NSLS-2
NSLS-1
Courtesy G. Williams - JLab
The JLab Free Electron Laser User Facility
Current User Facility has 7 Labs
• Lab1
General set-ups and prototypes
• Lab 2 Materials studies
• Lab 3 THz dynamics and imaging
• Lab 3a NASA nanofab
• Lab 4 Aerospace LMES
• Lab 5 PLD
• Lab 6 FEL + lasers for dynamics studies
Dyna- PLD MicroNano/ THz Optics/
mics
fab NASA Lab Materials
General
Purpose
Jefferson Lab – THz Source Physics
Considering Short
e- Bunches
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electron(s)
E/N
incoherent synchrotron
radiation from N e-’s
N
N
time
super-radiant
enhancement
freq. (1/time)
Thomas Jefferson National Accelerator Facility
Courtesy G. Williams - JLab
JLab THz source spectrum
Courtesy M. Klopf - JLab
Thomas Jefferson National Accelerator Facility
THz Imaging Schematic
Beamline
Camera 1
Mirror 1
Mirror 2
THz filter/lens
THz Camera
Mirror 3
2 Watts of broadband light into 3” x 3” field.
~104 camera elements, so 200 microWatts per pixel.
Scattering ~ 0.1%, so 0.2 microWatts per pixel.
Noise level, 1 nanoWatt, so S/N is 200 in real time.
Courtesy G. Williams - JLab
Test of Imaging Resolution
Raw Data
Processed Data
• Raw THz images are processed to reduce the background and
improve contrast
• Current configuration resolved down to the 1mm wide contact pads
• Polyethylene lens filtered the thermal IR, but does not image well
Courtesy G. Williams & M. Klopf - JLab
Real-time Imaging - Jefferson Lab & U. of Delaware Team
Mike Klopf, Matthew Coppinger, GPW, James Kolodzey, Nathan Sustersic
THz/MIR Double Resonance Experiments (w/ H. Rutt U. Southampton
fast MCT detector
(TEC cooled)
MIR beam
from FTIR
water lines
gas cell
Courtesy G. Williams & M. Klopf - JLab
THz beam
from accelerator
gas delivery and
pressure relief
We have plans for a 2 Photon Setup in the THz lab
sample chamber
IR/UV photons
THz photons
IR HeNe (1.52 mm)
THz Spectroscopy of surface plasmons
THz Beam from FTIR
HeNe sensor
THz sensor
VO2 sample
heater stage
A. Lukaszew – W&M & G. Scarel – JMU
Thomas Jefferson National Accelerator Facility
Courtesy M. Klopf - JLab
Applications in the IR
• Since the beginning of our science program in 1998 we had a mixture
of basic and applied science users.
– Material processing
• Metal nitriding/amorphization
– carbon & boron nitride nanotubes
– Medical/biophysics
• Differential heating of fatty tissue
• Treatments on the eye
• As with many of our basic science experiments, when doing applied
science, the best use for a high average power FEL is to sweep the
parameter space in order to optimize a process.
– Then build a table top device to commercialize the process.
The benefits of high power and tunability - differential
heating of fatty tissue to treat acne
Log
scale
Lin
scale
Subcutaneous fat /
dermis
Ratio of the temperature rises
5
Rox Anderson, Harvard Medical School - MGH
4
3
2
1
0
850 1000 1150 1300 1450 1600 1750 1900 2050 2200 2350
Wavelength, nm
Fat and Water have different spectra in the NIR
Applications for UV photons
• Determination of the “action spectrum” of human skin to UV
radiation.
– This will help in understanding how melanoma develops.
• Microfabrication of nano satellites
• Combustion dynamics
• Coherent and collective effects in materials
– Inorganic and organic
Laser MicroFabrication
&
Engineering
System
UV FEL application - the COSA propulsion module
• Added to rest of package – has flown in space
We can generate coherent harmonics at useful levels
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Harmonics are produced through the electron bunching process that creates gain at
the fundamental.
This bunching has Fourier components at harmonics of the fundamental frequency
and in our case extends into the ultraviolet.
First few harmonics can be many 10’s of watts.
Odd harmonics are peaked on-axis and can be degrade coating performance.
Can also be used to do science.
We performed measurements in the IR Demo
– “Coherent Harmonics in the Super-Radiant Regime from an FEL”, S.V. Benson,
J.F. Gubeli, and M.D. Shinn, Proc. PAC 2001
Harmonics on OC Mirror
while lasing at 1.6 micron
4th harmonic
3rd harmonic
We can transmit the odd harmonics through a hole in the
outcoupler
• Since the odd harmonics are peaked on-axis, we can transmit them
through an appropriately sized hole in the downstream mirror’s center.
• The even harmonics have no power on axis and the majority of the
power is in two lobes some distance away from center.
• The harmonics source is the electron beam size, so if one knows that,
one can calculate the mode size on the mirror, and hence, the size the
hole should be.
Initial Science with JLab VUV FEL
1. Atom Trap Trace Analysis (ATTA).
Lu Zheng-Tian (ANL) & Charles Sukenik (ODU)
- nuclear physics funded
2. Combustion dynamics.
David Osborn (Sandia)
- recommended by Eric Rohlfing, BES
3. Electronic structure of correlated materials.
Peter Johnson (BNL), Z.-X. Shen (Stanford)
- co-recipients of 2011 Buckley prize
Courtesy G. Williams - JLab
Atom Trap Trace Analysis (ATTA)
PIs -
Lu Zheng-Tian – Argonne National Lab
Charles Sukenik – Old Dominion University
Science – develop Kr dating.
81Kr
clock is 229,000 yrs compared to C, which is 5730 yrs
Qualifications – experiment running at Argonne.
Critical application – dating the polar ice-caps.
Why FEL? – high average power can study small volumes of water.
Advantage of the experiment is that it uses FEL direct beam, without
need of monochromator. The sample automatically selects the
bandwidth it needs.
Implementation - Idea is to bring equipment from Argonne, and
collaborate with local university user.
Courtesy G. Williams - JLab
Jefferson Lab FEL and THz Source – envisioned upgrades
proposed narrowband
THz source
proposed additional
broadband CSR THz source
Thomas Jefferson National Accelerator Facility
Conclusions
• The Jefferson Lab FEL Facility is a unique in it’s high average
brightness in the THz, and IR – VUV spectral regions.
– Sub ps-pulses at MHz repetition rates
• With an installation of a rebuilt “F100” cryomodule the linac energy
will increase to > 150MeV.
– Will permit lasing further into the UV and extend VUV.
• With the swap of our CEBAF-style cryounit for an improved
booster, we could lase in the VUV.
• Addition of a wiggler and optical cavity slightly canted from
the UV beamline would allow simultaneous lasing of UV and
THz for high E-field 2 color experiments.
A comment from Mr. Jefferson
• “I have always thought that if in the experiments to
introduce or communicate new plants, one species in a
hundred is found useful and succeeds, the ninety-nine
found otherwise are more than paid for.”
Thomas Jefferson
The Jefferson Lab FEL Team
April 24, 2009
This work supported by the Office of Naval Research, the Joint Technology Office, the
Commonwealth of Virginia, the DOE Air Force Research Laboratory, The US Army Night
Vision Lab, and by DOE under contract DE-AC05-060R23177.
FEL Performance
IR FEL
UV FEL
3rd
Projected
UV FEL
Harmonic
5th
UV FEL
Harmonic
Photon energy range of
fundamental
0.1 – 1.4 eV,
(12 -0.8 microns)
1 – 3.4 eV
(1200-360 nm)
3-10.2 eV
(410-120 nm)
5-17 eV
(250-73 nm)
Photon energy per
pulse
100 microJoules
20 microJoules
20 nanoJoules
0.2 nanoJoules
Repetition rate
4.678 – 74.85 MHz
4.678 MHz
4.68 MHz
4.68 MHz
Photon Pulse length
(FWHM)
100 fs – 2 ps
100 fs – 2 ps
100 fs – 2 ps
100 fs – 2 ps
Nominal pulse
bandwidth
1%
.2%
.2%
.2%
Electron Beam Energy
80 – 140 MeV
80 – 140 MeV
80 – 140 MeV
80 – 140 MeV
Charge per electron
bunch
135 picoCoulombs
60 picoCoulombs
60 picoCoulombs
60 picoCoulombs
Ultrashort light sources enable new thinking about material research
reductionist approach
- electrons
- nuclei
emergence approach, collective excitations
- phonons,, magnons
- polarons, plasmons
(called quasiparticles)
from Marvin Cohen, Physics Today, June 2006, page 48.
Application: Laser nitriding automobile cylinder liners
(grey cast iron)
J. Lindner, AUDI AG
After honing
Treatment: mirror inside cylinder; rotating engine block
in series production, 5 simultaneous excimer lasers
After laser treatment
Slide courtesy of P. Schaaf - U. Göttingen
Reduction of oil consumption (30x)
Uses for carbon and boron nitride nanotubes
• Carbon nanotubes are hollow rods (like a soda straw) of pure
carbon.
• They have very small diameters – less than a micron across.
– A human hair is 25-180microns across.
• They can be used to build light and strong structures.
• Boron nitride nanotubes are nontoxic to people – lots of uses.
Future Dark Matter experiments at Jefferson Lab
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Based on the null results of the laser-based experiments done around the
world, research is turning to other processes.
One involves a weak coupling of a particle dubbed the A’ (known as a vector
boson, or more colloquially, as a dark photon) that combines with a photon to
create an electron/positron pair.
• A positron is the antimatter twin to the electron.
These combine to form two gamma ray photons with an energy of 0.511MeV.
Our satellites measure copious 0.511MeV photons emanating from the center
of the Milky Way.
Two JLab experiments are being proposed.
• One uses the main accelerator working in the 1-4 GeV range (APEX)
• The other uses the FEL operating in the ~ 0.1 GeV range. (DarkLight)
Both are exciting because, while it is new research, it is still within the realm
of the Standard Model.
JLab research on Dark Matter
• Astronomical observations during the last century produced overwhelming
evidence that there is more matter in the Universe than we can detect.
– Observations from microwaves to X-rays, not just in the visible.
• The current value of the matter density of the Universe is 27.2%
• The other 72.8% is something we call Dark Energy
– Responsible for the accelerating expansion of the Universe.
• Of the 27.3%, only about 5% are the baryons that make up you and me.
– The remaining ~ 22% we call Dark Matter.
• Currently, we only detect its presence through gravity.
• We feel pretty certain some subatomic particle is responsible for this
matter, and thousands of researchers worldwide are searching for it.
• JLab has conducted two searches and has two more in the planning stages.
Candidate subatomic particles to explain the observations
• Possibilities
• There are as yet undetected subatomic particles which are predicted from theory
(The Standard model, or SM)
• Axions
• Variants of the neutrino
• Subatomic particles that are not predicted by the SM (Extensions to the
Standard Model)
• Weakly-interacting massive particles (WIMPS)
• Massive compared to the mass of the proton, 938 million electron volts
(MeV)
• Weakly-interacting sub-eV particles (WISPS)
• All of these families of particles have the following properties:
• Do not interact with the electromagnetic force
• Just gravity and the weak nuclear force
We used the FEL to do a WISP search
O.K. Baker 3rd Joint Conf. Patras, Greece
We used the CEBAF to do a WIMPS experiment
• The APEX (A-prime experiment) was run in the Summer of 2010.
• Searched in the range from about 65 to 550 MeV
APEX detectors
Experimental team
THz/MIR Double Resonance Experiments
Collaboration between JLab THz group and Harvey Rutt (U. of Southampton)
Goal – detect and time-resolve the modulation of the vibrational modes from highly excited
rotational modes in small gas phase molecules
Method
• utilize the high energy THz pulses from JLab FEL accelerator to “spin up” rotational states
in gas phase molecules
• high rep. rate of THz pulses (up to 75 MHz) allows for extremely sensitive lock-in
techniques to be employed
• CW MIR beam from globar source is modulated by an FTIR spectrometer to enable
spectral measurements and produce the 2nd modulation for the double-resonance
technique
• detection of side-bands off of the THz modulation frequency indicate energy exchange
between rotational and vibrational modes
• phase of signals contains information about the time constant of the energy exchange
process (in phase = prompt/intramolecular, off phase = scattering/intermolecular)
• real-time analysis software has been coded to achieve a -130 dB noise floor through
software implemented band pass filters centered at the sideband frequencies of interest
• both beam paths are fully under vacuum and a gas cell has been fabricated to
counterpropagate the MIR and THz beam through the gas sample
Thomas Jefferson National Accelerator Facility