status of high-power laser development at stanford shally saraf*, supriyo sinha, arun kumar...
TRANSCRIPT
Status of High-Power Laser Development at Stanford
Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan
and Robert L. Byer
E. L. Ginzton Laboratory, Stanford University
LIGO Science Collaboration Meeting
Hanford Site, August 19 – 22, 2002
LIGO-G020356-00-Z
Outline
• Review of slab lasers.
• Progress since Livingston LSC.
• 100W demonstration results.
• 200W amplifier design and status.
• (Near) future work.
Rod vs Slab
• 1st order thermal lens • Spatially dependent
birefringence (depolarization)
• 2nd order thermal distortions
• Slightly reduced mode-fill
zig-zag slabrod
Face-pumping vs Edge-pumping
Pumping
Cooling
zig-zagplane
Pumping
Cooling
zig-zagplaneFace-
pumping
Edge-pumping
zig-zag slab
Nd:YAG Laser Head
3.8 cm
Amplification Goal: 100 W
• Two zig-zag edge-pumped slab amplifiers.– Brewster ends.– 3:1 aspect ratio (width/thickness).
• About 900 W total pump power.• 10W LIGO laser followed by an external
amplifier provides 20W to drive slab amplifiers.
Experimental Setup for 100W demonstration
10W LIGO
LASER ISOL
20W
AMP
DUMP
2 2
2
Power
Meter
PBS
PBS
PBS
Edge Pumped Slab #1
Edge Pumped Slab #2
Beam Waist ~ 300m
Beam Waist ~ 300m
DUMP
DUMP
100W experimental setup
10W Amplifier
• Increased NPRO power from 235mW to 418mW by turning up drive current from 1.89A to 2.4A.
• Realigned optical train.
• Output power increased to 10.4W back to original specs.
• Set diode temperature to 24.1oC and pump current to 23A for the double passed amplifier.
10W Amplifier upgrade
20W Amplifier
• Replaced Faraday Isolator following 10W LIGO Laser.• Replaced faulty power supply for external 20W amplifier.• Mode matched beam into 20W amplifier (waist ~ 245m)
Beam quality after 20 W amplifier
Beam diameter versus Propagation Distance after 20W amplifier
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0 50 100 150 200 250 300 350
Distance (mm)
Bea
m D
iam
eter
(u
m)
Hor. beam diameter
M2X = 1.09
Ver. beam diameter
M2Y = 1.02
Measured output power ~ 24.4W.
Edge pumped slab head assembly
Slab 2 power amplifier set up
Complication ---- Slab #1 cracked
Results for slab amplifier # 1
Extracted Power versus Input PowerSlab 1 single pass
0
2
4
6
8
0 5 10 15 20 25
Input Power (W)
Ext
ract
ed
Pow
er (W
)
180W Pump goL = 0.412150W Pump goL = 0.357120W Pump goL = 0.22790W Pump goL = 0.184
Output Power = Input Power + Extracted Power
Power and M2 measurement after slab #1
Beam diameter vs propagation distance
0
500
1000
1500
390 490 590
Propagation distance (mm)
Beam
dia
met
er
(um
)
Horizontal diameter
M2x = 1.01
Vertical Diameter
M2y = 1.02
Output Power from triple passed slab #1 = 39W
Slab #2 single pass power output
Output Power versus Pump Power for Power Amplifier (single pass)
30
35
40
45
50
55
0 100 200 300 400 500
Pump Power (W)
Ou
tpu
t P
ow
er (
W)
Slab #2 triple pass power output
Triple Pass Output Power versus Pump Power
30
40
50
60
70
80
0 100 200 300 400 500
Pump Power (W)
Ou
tpu
t P
ow
er
(W)
Power out of MOPA ~ 71.8W
Thermal lens measurements
Thermal Lens Power versus Pump
0
2
4
6
8
100 200 300 400 500
Pump Power (W)
Dio
pte
rs (
1/m
)
Pumping
Cooling
zig-zagplane
Future work on 100W MOPA
• Compensate for thermal lens in second slab by using cylindrical lenses in triple pass.
• Faster beam quality measurements using holographic beam sampler to eliminate need for multiple wedges for attenuating power.
• M2 measurement of MOPA output.
• Redo theoretical calculation of thermal lens.
End pumping topology for 200W design
Motivation -> Higher efficiency
• Near total absorption of pump light.
• Confinement of pump radiation leads to better mode overlap
signal IN
Pump
0.6% Nd:YAG
undoped end
undoped endsignal OUT
Pre-amplifier Design : End-pumping
20 W 160 W
2-slab end-pumped double passed
amplifier
Crystal Dimensions Width = 1.11 mm,
Length = 6.6 cm, Thickness = 0.9 mm
Slab Design Issues1. Parasitic suppression2. Pump light coupling and absorption
Courtesy, Hagop Injeyan, TRW
Expected MOPA System Performance
Amplifier Input
Power
Multi-mode
Output
Output TEM00
End-pumped
(Ppump = 130W)16W 60W 48W
End-pumped
(Ppump = 435W)48W 200W 160W
Edge-pumped
(Ppump = 1400W)160W 500W 400W
• Edge pumped design chosen for final stage because of heat extraction requirement and simpler engineering design without sacrificing much pump absorption.
Status of 200W design
• Received 8mm x 8mm Nd:YAG composites with undoped ends from Onyx.
• Diced up one composite in the Stanford Crystal shop. On one plate undoped end broke off cleanly from the doped portion. (possibly defective bonding from Onyx?)
Status of 200W design (contd….)
• Second composite being diced up by Crystal River Optics.
Future Work on 200W MOPA
• Get coated plates from MLD, inspect and dice up into slabs with final dimensions.
• Install Laser Line pump diodes with total pump power of 500W.
• Fabricate laser head with microchannel coolers.
• Integrate and start amplifier experiments.