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Present status of the laser system for KAGRA

Present status of the laser system for KAGRA. Univ. of Tokyo Mio Lab. Photon Science Center SUZUKI, Ken-ichiro. Outline. Laser system Fiber laser amplifier Coherent addition Previous work Present status Summary & Future work. Laser System & Requirements.

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Present status of the laser system for KAGRA

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  1. Present status of the laser system for KAGRA Univ. of Tokyo Mio Lab. Photon Science Center SUZUKI, Ken-ichiro

  2. Outline • Laser system • Fiber laser amplifier • Coherent addition • Previous work • Present status • Summary & Future work

  3. Laser System & Requirements • MOPA (Fiber and Solid-state laser amplifiers) + Coherent Addition 40W Fiber laser amplifiers Solid-state laser amplifiers 180W 40W 80W Nd:YAG NPRO 400mW Coherent addition on the beam splitter Requirements ・Laser power 180W ・Single frequency 1064nm Single transverse mode TEM00 ・Linear polarization ・Low intensity noise ・Low frequency noise

  4. Setup • Widen dynamic range – Fiber stretchers • Same path length – good spatial mode matching • Change water chiller Optical fiber system Free space optical system HWP HWP Isolator EOM Collimator Fiber stretcher output Fiber amplifier Beam splitter Nd:YAG NPRO 400mW 15MHz Photo detector + - Mixer Servo

  5. Previous work 78.9W was observed from two 40-W incident beams

  6. Optical System – fiber system 19 inch rack mounted Fiber amplifiers Seed laser (NPRO 400mW) Fiber components Isolator coupler EOM stretcher Power supply for NPRO

  7. Optical System – addition stage Collimators (Fiber amp. output) Isolators Beam splitter Bright port Dark port Dark port optical system

  8. Experimental Result – long term operation • Operation itself lasted 5 hours (Output power: 77～78W) • The fiber stretchers had enough margin of control • Large power fluctuation was observed for the first one hour • Further brush-up is needed Stable operation applied voltage of the fiber stretchers output power of bright and dark port

  9. Experiment Result – polarization fluctuation • Power fluctuation results from polarization fluctuation • Isolator is polarization dependent • Polarization stability is important for power stability Cut off power Collimator Transmitted power HWP Isolator an example of power fluctuation

  10. Experiment Result – fiber stretcher Setup Fiber stretcher PD NPRO oscillator Signal: 10Vp-p @100Hz Oscillo scope Polarization rotation was seen at fiber stretcher. This may causes power fluctuation.

  11. Next Step – solid amplifier stage • Use three Mitsubishi laser amplifiers • Strong thermal lensing (～50cm/rod) • Amplification of up to 180W is expected. Three solid-state laser amplifiers 180W 80W

  12. Summary & Future work • Coherent addition in new system was done • Operation lasted 5 hours • Longer operational term can be expected • Control system worked well • Noise evaluation of coherent addition • Solid amplifier stage (～180W) • Stabilization of intensity and frequency

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