Status of High-Power Laser Development at Stanford Shally Saraf*, Supriyo Sinha, Arun Kumar...

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

*saraf@stanford.edu

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.