Diode and Dye Laser Developments

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Prof. Chang and Mr. Lee of KAIST and Prof. Choi
(not shown) of Cheju National University visited
Irvine lab in Feb 98.
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Physics and Chemistry Departments at the
University of California, Irvine
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Outside High Bay Laboratory
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Magnet Cooling Heat Exchanger Equipment
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Mirror and Torus plasma devices inside high bay
laboratory
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How does thetool work?

• Fluoresce ion

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Argon and krypton ion pump lasers powering 2 dye
lasers
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Argon plasma viewed through quartz vacuum window.
Background plasma light emission must be
subtracted to get LIF signal
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Tunable Dye Laser
Pump Laser
Acousto-Optic Modulator
Square Wave Generator
Optical Fiber
Lock-In Amplifier
Lens
Digitizer
PMT
Boxcar Averager
Filter
Plasma
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Ion Distributions
Scan laser across Doppler-broadened ion
distribution function. LIF output gives
1-dimensional distribution function.
These scans used a dye laser
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Example of convection measurement with dye laser.
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Laser Configurations
Pump Laser
Dye Laser
Optical Fiber
AOM
A)
Optical Isolator
B)
MOPA
AOM
Polarization Rotator
Optical Isolator
Seed Laser
Optical Isolator
C)
AOM
MOPA
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5 mW diode laser set up as seed to 0.5W diode
laser used as amplifier.
New Focus Velocity Model Seed Laser
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1/2 W laser set up as Master Oscillator Power
Amplifier (MOPA) by removing laser cavity
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New Focus Vortex model laser (in blue case)
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Diode lasers may be operated manually via
controllers on optical table.
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Once optical assembly and alignment is completed,
all lasers and data processing are controlled
remotely by personal computers using LabView and
GPIB.
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Seed Laser Manufacturers
New Focus, Inc. (Santa Clara, California) http//w
ww.newfocus.com Telephone [phone] Model Po
wer Scan Range Price (US) 6009 Vortex 6 mW 80
GHz 7900 6308 Velocity4.5 mW 70 GHz, 12
nm 17000 EOSI, Inc. (Boulder, Colorado) http//ww
w.eosi.com Telephone [phone] Model Power
Scan Range Price (US) ECU-2010 5 mW 100 GHz,
15 nm 8500-13000 Above data for 668 nm. Other
wavelengths available.
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MOPA Laser Manufacturer
SDL, Inc. (San Jose, California) http//www.sdli.c
om Telephone [phone] Model Power Scan
Range Price (US) TC30 500 mW 10 nm 19000
Diode Controllers for MOPA
Manufacturers Model Price (US) SDL, Inc. (San
Jose, California) 824 4250 Newport Corp.
(Irvine, California) 8000 5405 http//www.newpor
t.com Telephone [phone]
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Optical Isolator Manufacturers
Isowave (Dover, New Jersey) TEL [phone]
1995 New Focus, Inc. (Santa Clara,
California) 2950 Optics For Research (Caldwell,
New Jersey) TEL [phone]
Acousto-Optic Modulator Manufacturers
Isomet (Springfield, Virginia)
http//www.isomet.com TEL [phone] AOM
720 Driver 380 Crystal Technology Inc. (Palo
Alto, California) TEL [phone] AOM 690
Driver 420
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SDL laser (with cavity in place) does not provide
good mode structure for Doppler LIF. SDL major
mode spacing 25.56 GHz, minor modes 1.79 GHz
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Argon distribution taken using 0.5 W SDL laser
without seed, after tuning carefully to get
single mode. Laser diode temperature changed by
0.14 degrees Kelvin to get entire scan.
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Argon ion distributions with diode laser
Low power seed lasers have stable single-mode
operation, excellent for Doppler LIF
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How to get 2- and 3-dimensional ion velocity
distribution functions? Optical Tomography is
answer. Tomography is used in medicine to
determine shapes of objects in space. Examples
CT scans (CAT scans), MRI (NMR technique), and
Ultrasound. Optical Tomography determines shapes
of distribution functions in velocity space.
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Optical Tomography To get2- and 3-dimensional
distributions
Take many pictures from many angles
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Reconstruct image via algorithms
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Optical Tomograph
Drifting ion distribution heated perpendicularly
in straight magnetic field by electromagnetic
waves.
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What happens to ions as they are heated and flow
along diverging magnetic fields?
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Optical Tomograph
Ion Conic Distribution, triangle shape in vy-vz
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Broadband and Single-Mode Operations Dye lasers
May be run with inter-cavity assembly etalons in
(single-mode) or etalons out (broadband,
multi-mode). Single-mode allows scanning for
distribution function, tagging in velocity space
(for Dv v , Cv ). Broadband allows spatial
density profile scans, tagging in real space (for
Dperpendicular , Dparallel ) Diode lasers May
run essentially in single-mode only.
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Scan laser beam across plasma to get density
profile
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Ions may be tagged to follow their paths in time
and space. Here plasma flows from left to right
past the tag beam (T) and is observed later with
a detection beam (D).
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The tagging laser beam creates a column of tagged
ions with a spatial profile, typically Gaussian.
In time, the tagged ion column will spread in
space (due to diffusion) and move its center (due
to convection).
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Quiet plasma (?n/n0 lt0.002) diffusion across
magnetic fields is classical with small turbulent
contribution.
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Ion Transport in Velocity Space
For velocity-space transport, we examine
Fokker-Planck theories by Rostoker.
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Velocity-space convection of ions. Think about
the distribution function and various points in
it.
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Velocity-Space Diffusion of Ions
Test magnitude and dependence of diffusion on ion
velocity through the plasma.
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Dye and Diode Lasers

• Dye Lasers work for LIF
• Many lines can be fluoresced
• Single mode/broadband
• Full system cost gt 130 k
• Time to first data gt 5 hours
• Reliability multi-year
• 1m3,20kW,H2O

• Diodes work for LIF
• Few lines can be fluoresced
• Single mode
• Full system cost 35 k
• Time to first data 30 sec
• Reliability multi-year
• 10-2 m3, 50 W