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Development of high-power and stable laser for gravitational wave detection

Development of high-power and stable laser for gravitational wave detection. Mio Laboratory Kohei Takeno. Aims of My Work. Current Status. Final Goal. Nd:YAG （ 1.064 m m ） Output Power ＞ 100W Single Transverse Mode Single Longitudinal Mode Low Intensity Noise Low Frequency Noise

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Development of high-power and stable laser for gravitational wave detection

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  1. Development of high-power and stable laser for gravitational wave detection Mio Laboratory Kohei Takeno

  2. Aims of My Work Current Status Final Goal • Nd:YAG （1.064mm） • Output Power＞100W • Single Transverse Mode • Single Longitudinal Mode • Low Intensity Noise • Low Frequency Noise • Linearly Polarized • Nd:YAG • 30W • TEM00 • Injection lock • ？ • ？ • × The 3rd TAMA symposium

  3. Laser Cavity • Mode / Thermal Effects • Optimum Coupling HR Rd OC Pump Output Laser Medium The 3rd TAMA symposium

  4. Mode • Transverse Mode : Spatial Distribution • Multi-mode oscillation depends on the mode of the laser cavity • Longitudinal Mode : Frequency Difference • The spatial hole burning causes multi-mode oscillation Succeeded in controlling! In progress now The 3rd TAMA symposium

  5. Transverse Mode • Lowest Order TEM00 • Higher Order TEM10 Higher order modes spread compared to the lowest The 3rd TAMA symposium

  6. Beam Quality：M2 • M2 =1 : Diffraction-Limited (TEM00) • M2 = D0Q / d0q The 3rd TAMA symposium

  7. Thermal Effects • Energy which is stored in the laser medium causes… • Thermal Lens • Thermal Birefringence Thermal lens affects stability of the laser cavity The 3rd TAMA symposium

  8. Strategy forHigh Power Laser • Two points: • Give gain to the lowest-order mode • Give loss to higher-order modes • How to design the laser cavity? • Clip higher-order modes with rod hard aperture → Long cavity • Stable cavity by use of thermal lens → Flat mirrors The 3rd TAMA symposium

  9. Laser Medium HR Rd OC Cavity Modes • Strong thermal lens/Too long cavity • Flat mirrors + Thermal lens • Long cavity unstable Laser Medium HR Rd OC The 3rd TAMA symposium

  10. My Experiment • Design of Optimum Laser Cavity • Transverse mode control • Make use of thermal lens • Laser module • Specification：35W Output @ 25A LD Current （Short cavity / Multi transverse mode oscillation） The 3rd TAMA symposium

  11. Laser Module • Cutting Edge Optronics • Nd:YAG Rod (2mm diameter, 63mm length) • 0.6% Nd3+ doped • LD pumped • Water-cooled The 3rd TAMA symposium

  12. Thermal Lens • Measurement of the Focal Length The 3rd TAMA symposium

  13. Linear Cavity • (L１,L２ ) Cavity and Mode Simulation The 3rd TAMA symposium

  14. Power vsOC Transmittance • Laser Output→“Loss” of the cavity • Optimum coupling The 3rd TAMA symposium

  15. Power vsOC Transmittance The 3rd TAMA symposium

  16. Power vs Cavity Length • Short cavity→Multi transverse mode • Long cavity→Causes loss for TEM00 The 3rd TAMA symposium

  17. Power vs Cavity Length The 3rd TAMA symposium

  18. Optimum Laser Cavity • M2＝1.1 (Horizontal) • M2＝1.2 (Vertical) • Flat mirrors • Long cavity（71cm） • Output Power 30W TEM00 The 3rd TAMA symposium

  19. TEM00 ・30WLaser The 3rd TAMA symposium

  20. Ring Cavity • Traveling-wave cavity • Bi-directional output（３W / path） The 3rd TAMA symposium

  21. Summary • Measure the thermal effects • Succeeded in controlling transverse modes • TEM0030W laser output with linear cavity • Bi-directional lasing with ring cavity The 3rd TAMA symposium

  22. Further Work • Thermal birefringence compensation • Insert a QWP in the laser cavity • Injection locking • Control the laser cavity • Measure the noise characteristics • New laser head has arrived!! The 3rd TAMA symposium

  23. CIDER • Close-coupled Internal Diffusive Exciting Reflector • 60W・TEM00 (M2 = 1.07) The 3rd TAMA symposium

  24. Thermal Birefringence • Image of the thermal birefringence Image Pumping Power 20.3A 25.4A The 3rd TAMA symposium

  25. Further Work II • Cascade Laser Cavity • MOPA • Coherent Addition • Injection-locking Chain The 3rd TAMA symposium

  26. Laser Development My Work M2<1.1 100W + Stable, High Quality The 3rd TAMA symposium

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