10W Injection-Locked CW Nd:YAG laser

David Hosken, Damien Mudge, Peter Veitch, Jesper Munch

Department of PhysicsThe University of Adelaide

Adelaide SA 5005Australia

LSC – LLO March 2004 LIGO-G040069-00-Z

LSC – LLO March 2004 LIGO-G040069-00-Z

Talk Outline

• Overall motivation• ACIGA HPTF • Laser design• Laser performance• Conclusions

LSC – LLO March 2004 LIGO-G040069-00-Z

• Gravitational wave interferometers require high power CW lasers that produce a single frequency TEM00 mode

Overall Motivation

LSC – LLO March 2004 LIGO-G040069-00-Z

Overall Motivation

• Gravitational wave interferometers require high power CW lasers that produce a single frequency TEM00 mode

• Our strategy: injection-locked chain

- injection-locking of 5W prototype previously demonstrated

NPRO0.5W

10W 100W

LSC – LLO March 2004 LIGO-G040069-00-Z

Overall Motivation

• Gravitational wave interferometers require high power CW lasers that produce a single frequency TEM00 mode

• Our strategy: injection-locked chain

- injection-locking of 5W prototype previously demonstratedSpecific project objectives:• Field deployable 10W TEM00 CW Nd:YAG travelling-wave slave

laser• Characterise injection-lock• Meet or exceed the frequency and intensity noise requirements

of ACIGA / TAMA 300

NPRO0.5W

10W 100W

LSC – LLO March 2004 LIGO-G040069-00-Z

ACIGA HPTF

• The lasers we are developing will be delivered to the Australian Consortium for Interferometric Gravitational Astronomy (ACIGA) high power test facility (HPTF) at Gingin, Western Australia.

• We will also provide a laser upgrade for the TAMA300 gravitational wave interferometer in Japan.

The Australian International Gravitational Observatory (AIGO)

LSC – LLO March 2004 LIGO-G040069-00-Z

Gain Medium for 10W Slave Laser

• Coplanar folded zigzag slab (CPFS) *

• Side pumped using fast-axis collimated diode bars*J. Richards and A. McInnes, Opt. Lett. 20, (1995), 371.

(Diode power derated for increased lifetime)

D iode Laser(20W )

D iode Laser(20W )

P um p ligh t re flecto r M ax R

80%

LSC – LLO March 2004 LIGO-G040069-00-Z

• Top and bottom cooled

• Mounted on a single air-cooled base

Compact laser with increased portability and reliability

Gain Medium for 10W Slave Laser

H eats ink

H eats inkN d:YA G S lab

H eats ink

P um p reflector

D ouble d iode bar package

LSC – LLO March 2004 LIGO-G040069-00-Z

Standing-Wave Results

D iode Laser(20W )

D iode Laser(20W )

P um p ligh t re flecto r M ax R

80%

LSC – LLO March 2004 LIGO-G040069-00-Z

With ~20mm mirror to slab arm lengths we achieved:• Multimode power = 15.9W (40W pump power)• Multimode slope efficiency = 45%

Standing-Wave Results

D iode Laser(20W )

D iode Laser(20W )

P um p ligh t re flecto r M ax R

80%

LSC – LLO March 2004 LIGO-G040069-00-Z

Travelling-Wave Resonator

D iode Laser(20W )

M ax R (60 inc idence)0

In jected beam

O utput

P ZT

P ZT

D iode Laser(20W )

P um p ligh t re flecto r

O utput coupler (10 incidence)0

LSC – LLO March 2004 LIGO-G040069-00-Z

Travelling-Wave Resonator

Injection locking servo control system:Low bandwidth, high dynamic range PZT plus high bandwidth, low dynamic range PZT together provide sufficient bandwidth and dynamic range.

D iode Laser(20W )

M ax R (60 inc idence)0

In jected beam

O utput

P ZT

P ZT

D iode Laser(20W )

P um p ligh t re flecto r

O utput coupler (10 incidence)0

LSC – LLO March 2004 LIGO-G040069-00-Z

10W Slave Laser

LSC – LLO March 2004 LIGO-G040069-00-Z

ACIGA HPTF and TAMA Lasers

LSC – LLO March 2004 LIGO-G040069-00-Z

Control and Confinement of Mode

• Astigmatic thermal lensing in the pumped slab: fvertical ~ 6-8cm fhorizontal ~ 2-3m

• Vertical (cooling) plane- mode confinement provided primarily by strong thermal lensing- mode control achieved by matching the laser mode to the

pumped region

• Horizontal plane - mode confinement by residual curvature of the slab sides, very

weak thermal lens and mirror curvature- higher order mode rejection by apertures formed by Brewster

entrance/exit windows

Careful adjustment of cavity length and pump power achieves anexcellent fundamental mode, in both horizontal and vertical planes.

LSC – LLO March 2004 LIGO-G040069-00-Z

Travelling-Wave Results

Using 90% reflective, 5.00mconcave output coupler

• M2horizontal < 1.1

• M2vertical < 1.1

• Output power = 9.2 W (31W pump power)

Measured using Spiricon M2

Beam Analyser

LSC – LLO March 2004 LIGO-G040069-00-Z

Injection-Locking SetupN P R O

H W P

E O M

F araday iso la to r

H W P

10W S lave

M ode m a tch ing

P ow er m e ter

LSC – LLO March 2004 LIGO-G040069-00-Z

Injection-Locking SetupN P R O

H W P

E O M

F araday iso la to r

H W P

10W S lave

M ode m a tch ing

P ow er m e ter

LSC – LLO March 2004 LIGO-G040069-00-Z

Injection-Locking SetupN P R O

H W P

E O M

F araday iso la to r

H W P

10W S lave

M ode m a tch ing

P ow er m e ter~5W

LSC – LLO March 2004 LIGO-G040069-00-Z

Injection-Locking SetupN P R O

H W P

E O M

F araday iso la to r

H W P

10W S lave

M ode m a tch ing

P ow er m e ter~10W

LSC – LLO March 2004 LIGO-G040069-00-Z

Multi- longitudinal mode operation of free-running slave laser (left), and single frequency operation (right) when locked using a stable master laser.• Currently developing and testing a PDH servo control circuit, and have achieved prolonged suppression of reverse-wave with closed servo loop

(Traces measured using a scanning Fabry-Perot cavity (10GHz FSR))

3 ) Ref A : 2 Vo lt 2 .5 m s 4 ) Ref B : 5 0 0 m Vo lt 2 .5 m s

3 ) Re f A : 2 0 0 m Vo lt 2 .5 m s 4 ) Re f B: 5 0 0 m Vo lt 2 .5 m s Passive injection-locking

LSC – LLO March 2004 LIGO-G040069-00-Z

Conclusions

Progress to date:• Efficient robust compact design• Robust thermal control system• M2

x,y < 1.1 with 9.2W output in travelling-wave• Short term injection-locking achieved

Future plans:• Increase output power to over 10W• Long-term injection-locking• Characterisation of noise

Delivery of injection-locked laser to AIGO in May 2004.