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![Page 1: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/1.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
Status of high power laser development for LIGO at Stanford
Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharanand Robert L. Byer
E. L. Ginzton Laboratory, Stanford University
LSC2003 Hannover, Germany
August 18-21, 2003 LIGO-G030434-00-Z
![Page 2: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/2.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
Outline
• Stanford approach to power scaling.
• Experimental setup.
• 100W demonstration results.
• Scaling to 200W.
• Future work.
![Page 3: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/3.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
MOPA vs OSCILLATOR
LOW POWER,
ULTRA STABLE
MASTER OSCILLATOR
PRE-AMP PRE-AMP PRE-AMP POWER-AMP• Rugged
• Scalable
• Single frequency
• Power available despite element failure.
• Less efficient.
• Difficult to control
• Single frequency operation involves injection locking.
• Element failure usually means zero power.
• More efficient.
MOPA
OSCILLATOR
![Page 4: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/4.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
Ppump = 180 W
ISOLA
TOR
Mode-matching optics
20 W
Amplifier
Lightwave
electronics
edge pumped slab
10W LIGO
MOPA
System
Experimental setup presented at LSC Livingston
end pumped slab
Ppump = 430 W
P
M
C
OCPMTEM00 power
![Page 5: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/5.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
808nm Pump
0.6% Nd:YAG
undoped end
undoped end
808nm Pump
signal IN
signal OUT
1.5 cm
3.33 cm1.5 cm
End pumped slab geometry*
Motivation -> Higher efficiency
• Near total absorption of pump light.
• Confinement of pump radiation leads to better mode overlap
1.1 mm X 0.9 mm
*Similar to TRW
Hagop Injeyan, et. al.
![Page 6: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/6.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
Results of MOPA experiment
• Single Pass Power output ~ 65 W (M2 < 1.1)• Depolarization ~ 1.5%.• P-P intensity fluctuations ~ 7%
COLD SLAB
OUTPUT 30 WPUMPED SLAB
OUTPUT 65 W
![Page 7: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/7.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
Mode content of 65 W beam
-2
-1.5
-1
-0.5
0
0.5
0 0.002 0.004 0.006 0.008 0.01 0.012
frequency (a.u)
Po
we
r (a
.u)
FSR of PMC
TEM00
*** 74 % mode content in TEM00 ***
P-P intensity fluctuations ~ 2% after PMC
![Page 8: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/8.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
Double pass setup for MOPA experiment
*** 104 W demonstrated at M2 < 1.2 ***
![Page 9: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/9.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
Slab Issues for scaling to 200W
Question: Why is the small signal gain of the end pumped slab much lower than expected?
Answer: 30 - 35% pump scattered in undoped region.
Rough surfaces (left & right)
Pump light leakage.
TIR surfaces (top & bottom)
808nm Pump
808nm Pump
![Page 10: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/10.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
Solutions towards improved pump confinement
UD
UD
ROUGHEN
TIR surfaces (top & bottom)
D
POLISH
POLISH
SLAB WITH POLISHED UNDOPED REGION & ROUGHED DOPED REGION
00.20.40.60.8
11.21.41.61.8
2
0 50 100 150 200
Pump Power (W)
go
l (u
ns
atu
rate
d)
++ Small signal gain improved.
- Vendor damaged coating during sand blast procedure for roughening up the doped region.
coating damaged
1. POLISH UNDOPED SIDES AND ROUGH UP THE DOPED REGION.
![Page 11: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/11.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
Measurements on fully polished slab.
POLISH
UD
UD
POLISH
TIR surfaces (top & bottom)
D
POLISH0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 20 40 60 80 100 120
Pump Power (W)
go
l (u
ns
at)
++ Pump light guiding improved to 75-80%.
----- Parasitic kicks in immediately and clamps the gain.
2. POLISH THE TWO PREVIOUSLY ROUGH SIDES OF SLAB.
![Page 12: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/12.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
Measurements on beveled slab
0
0.5
1
1.5
2
2.5
0 50 100 150 200 250
Pump Power (W)
go
l (u
nsa
t)
+ Parasitic threshold increased.
-- Parasitic still kicking in well before reasonable gain achieved.
UD
UD
POLISH
TIR surfaces (top & bottom)
D
POLISH
89 85cross section
POLISH
3. POLISH AND BEVEL THE TWO SIDES OF THE SLAB TO KICK OUT THE PARASITIC.
![Page 13: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/13.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
Slab with cladding
33UD
UD
POLISH
TIR surfaces (top & bottom)
D
POLISH
POLISH + APPLY
CLADDING + ROUGHEN 3360
• CLADDING USED: Norland 61 optical epoxy n = 1.56
• PARASITIC LEAKS INTO CLADDING AND IS SCATTERED OUT
4. APPLY CLADDING ON DOPED REGION OF SLAB TO SPOIL
TIR ANGLE FOR TRANSVERSE PARASITIC.
YAG
AIR YAG
AIR
![Page 14: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/14.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
Measurements on slabs with cladding
0
1
2
3
4
5
6
0 100 200 300 400
PUMP POWER (W)
sm
all s
ign
al g
ain
slab1
slab2
+++ Cladding approach works well for suppressing parasitics.
- Slabs cracked from possible contamination and stresses during polishing.
![Page 15: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/15.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
Parasitic control summary
0
1
2
3
4
5
6
0 100 200 300 400
PUMP POWER (W)
go
l (U
ns
atu
rate
d)
polished sides
polished + 5deg bevel
polished + dopedreoughed
epoxy cladding 1
epoxy cladding 2
![Page 16: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/16.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
Ppump = 120 W
ISOLA
TOR
Mode-matching optics
20 W
Amplifier
Lightwave end pumped slab #1
10W LIGO
MOPA
System
Scaling to 200 W : Experimental Plan
end pumped slab #2
Pslab1 = 60 WPpump = 430 W
Pslab2 = 200 W
P
M
CTEM00 Power ~ 160 W
![Page 17: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/17.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
Saturated amplifier noise experiment tentative setup
+-
Balanced detection RF spectrum analyzer
2 high power
beamdumpdump
dump
High finesse cavity
Low finesse cavity
2 2 2
NPRO
end pumped slab
![Page 18: Stanford High Power Laser Lab Status of high power laser development for LIGO at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar Sridharan and Robert.](https://reader035.fdocuments.net/reader035/viewer/2022070401/56649f1e5503460f94c35a0d/html5/thumbnails/18.jpg)
Stanford High Power Laser LabStanford High Power Laser Lab
Future Work
• Get mode content and noise measurements of 100 W beam.
• Power scale to 200 W using 2 end pumped slabs. - Build 2 new slabs with parasitic control cladding.
- Set up pumping scheme for slab #1 (preamplifier). - Measure mode and noise characteristics of 200 W
beam. • Complete saturated amplifier noise experiment.