development of a high-power and stable laser for large ... · development of a high-power and...

Development of a high-power and stable laser for Large-scale cryogenic

gravitational wave telescope

University of TokyoKohei Takeno

2003/07/105th Edoardo Amaldi ConferenceKohei Takeno

GW Detectors in Japan

TAMA300– RFPMI– 300-m baseline

Large-scale cryogenic gravitational wave telescope(LCGT)

– RFPMI (with RSE) – 3-km baseline– Cooled mirrors Talk by Uchiyama on Friday


LCGT

Target– Coalescence of binary neutron stars– Signal

Noise– Shot noise

×

+××≈ −2

2001102.2

[Hz]24

shotfh P

[W]100

)kHz1Hz100(@Hz/10 22 −≈ −h

Hz/


Requirement

Light source for LCGT– Nd:YAG (λ = 1.064µm)– Output Power: 300W– Single longitudinal mode– Single transverse mode (M2 < 1.1)– Linearly polarized– Frequency noise– Relative intensity noise

Hz/Hz10 7−<Hz/10 8−<


Strategy for a high power laser

Injection Locking Chain + MOPA


The key to a stable and high-power laser

Efficiency– Uniform pumping

Mode– Cavity design

Coupling Efficiency– Output coupler

Compensation of thermal effects– Thermal lens, thermal birefringence


Overview of laser development

Two lasers for injection locking chain– First slave laser

30 W, TEM00　 (Linear cavity)17 W, Linearly polarized (Ring cavity)Thermal birefringence compensation

– Second slave laser60 W, TEM00 , Linearly polarized (Linear cavity)Thermal birefringence compensation~40 W (Ring cavity)


First slave Laser (Ring cavity)

Current Status– Nd:YAG Rod (2-mm diameter, 63-mm length)– Total output power of 17 W– Thermal birefringence compensation– Transverse mode （M2=1.4 ）– Linearly polarized


Laser head

Manufactured by Cutting Edge Optronics– Nd:YAG Rod (2-mm diameter, 63-mm length)– 0.6% Nd3+ doped– LD pumping– Water cooling


Thermal birefringence compensation

Rotate polarization


Prototype of the first slave laser

Laser cavity


Output Power

Maximum output power of 17 W


Second slave Laser (Linear cavity)

Current status– Nd:YAG Rods (4-mm diameter, 70-mm length)– Output power: 60W (with one laser head)– Single transverse mode （M2=1.12 ）– Linearly polarized– Relative intensity noise Hz100@ Hz/10 4−≈


Laser head

Manufactured by Mitsubishi– Two Nd:YAG Rods

and a rotator– LD pumping– Diffusive Reflector– Water cooling


Linear cavity

Convex mirrors （Curvature: 20cm)R=85％ Output couplerThermal birefringence compensation


Relative Intensity noise


Second slave Laser (Ring cavity)

Current status– Total output power: 39 W (Self-injection)


Output Power

Maximum output power of 39 W (Self-injection)


Problems of the current design

AstigmatismIncomplete compensation of thermal effects

– Asymmetric beam mode at the Nd:YAG rods


How to improve?

Two-module cavity– Ring cavity with two laser modules


How to improve?

Two-module cavity– Cavity mode Simulation


Further work

First slave Laser– Injection Locking– Stabilization Experiment

Frequency stabilizationIntensity stabilization

Second slave Laser– Two-module cavity

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