ECE 631 (Photonics and Devices)
Gas Laser (He-Ne)
Presentation: Muhsin Caner GÖKÇE
Instructor: Prof. Dr. Celal Zaim ÇİL
Çankaya University Graduate School of Natural and Applied Sciences
Department of Electronic and Communication Engineering
Table Of Contents
Background Information
How it works
Applications
Technical Properties
Pulse Mode (recent Improvements)
Background information
Inventions:
• 1954 Gordon, Zeiger, Townes: Maser
• 1960 Maiman: Ruby-Laser (Al2O3, Solid)
• 1961 Helium-Neon Laser (Gas) by Ali Javan in
Bell Telephone Laboratories, USA
• 1962 Semiconductor-Laser
• 1985 Rontgen(X-ray)-Laser
Background information
• It is a four level atom laser with a mixture of
helium and neon(helium to neon (typically
around 7:1 to 10:1) at a pressure of between 2
and 5 Torr (atmospheric pressure is about 760
Torr )).
• It operates in Continuous Working (CW)
mode(the Helium-Neon laser was the first
continuous laser).
• Superior beam quality(Gaussian irradiance
profile, long coherence length, low divergence
angle).
 How It Works
 How It Works
Excited levels of
Helium at 20.61
eV is very close to
a level in Neon at
20.66 eV
Collision of a
helium with neon
atom, the energy
can be
transferred from
the Helium to the
Neon atom.
 How It Works
Neon is the lasing gas
Visible light and IR
Fast radiative transition
(spontaneous)
Relevant energy levels of the He-Ne laser.
(Ref: Principles of Lasers Orazio Svelto 5. edition)
The lifetime of s-states
is order longer than p
states
 Applications
Red (6328 Å) (Most Common)
Yellow (594 nm) (Not efficient)
Orange (604.6 and 611.9 nm) (Not Efficient)
Green (543.5 nm) (Not efficient)
Infrared (1,523.1 nm) (Fiber optic testing)
Types of wavelengths
 Applications
Some of the important applications of He-Ne lasers:
• Free-space optical communications
• Bar-code scanners
• Hologram generation
• Fiber Optic Experimentation
• Construction of laser light show
• Surveillance (ie. audio surveillence)
• Tachometer (measuring the rotation speed of a shaft or
disk)
• Burglar alarm
• Gyroscope
• Alignment
• Interferometry (extracting information about the waves)
• Laser printers
 Technical Properties
Cavity Length (L)
2-5 Torr
Totally reflective mirror
Rb =75 kΩ
Partially reflective mirror
1.2 to3 kV DC
Since the discharge has a negative resistance, a ballast resistance is to
be used in series with the laser to make the overall impedance positive
 Technical Properties
FWHM: Gain is at least half of the peak value
 Technical Properties
Maximum output is 100mw
Low divergence angle
Long Life (More than 10,000 hours)
Rugged, compact and less expensive
CVI Melles Griot Company TEM00
 Technical Properties
CVI Melles Griot Company(TEM00)
 Technical Properties
CVI Melles Griot Company TEM00
 Technical Properties
CVI Melles Griot Company TEM00
Pulse Modes
Mode Locking:
is a technique which converts CW beam to a
periodic series of very short pulses from
picoseconds to a nanosecond.
Advantages:
 High power pulse
 All the cavity modes are forced to be in phase
Disadvantages:
Implementation is diffucult
Pulse Modes (Recent Improvements)
Applications:
• Photon excitation microscopy
• Nuclear fusion
• 3D optical data storage
• Metal Forming Nano structure
References
• (Ref: Principles of Lasers 2010, Orazio Svelto 5. edition
page: 444-460)
• http://www.cvimellesgriot.com/
• http://www.repairfaq.org/sam/laserhen.htm#henhlc0
• http://www.worldoflasers.com/lasertypes2.htm
• ECE 631 lecture notes: http://ece631.cankaya.edu.tr
• http://hyperphysics.phyastr.gsu.edu/hbase/optmod/lasgas.html#c1
• http://www.fou.uib.no/fd/1996/h/404001/kap04.htm
Thanks for Your Attention