Status of high power laser development for LIGO at Stanford

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

*[email protected]

LSC2003 Hannover, Germany

August 18-21, 2003 LIGO-G030434-00-Z


Outline

• Stanford approach to power scaling.

• Experimental setup.

• 100W demonstration results.

• Scaling to 200W.

• Future work.


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


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


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.


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


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


Double pass setup for MOPA experiment

*** 104 W demonstrated at M2 < 1.2 ***


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


Solutions towards improved pump confinement

UD

UD

ROUGHEN


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.


Measurements on fully polished slab.

POLISH

UD

UD

POLISH


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.


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


D

POLISH

89 85cross section

POLISH

3. POLISH AND BEVEL THE TWO SIDES OF THE SLAB TO KICK OUT THE PARASITIC.


Slab with cladding

33UD

UD

POLISH


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


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.


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


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


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


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.

Status of high power laser development for LIGO at Stanford

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