Laser Requirements and Prospects for Gemini AO Program

1. Laser Requirements and Prospectsfor Gemini AO Program Céline d’Orgeville Gemini Laser Systems Engineer Laser Development Meeting

2. 36 CP Multi-LGS MCAO 85 Gemini AO program 1999 2000 2001 2002 2003 2004 NORTH Altair w/ NGS Altair w/ LGS Hokupa’a SOUTH CP Hokupa’a 85 2W LGS Laser Development Meeting

3. CP LGS AO System parameters • AO = Hokupa’a 85 elements • curvature WFS • 85 subapertures • 1 kHz frame rate • 70 to 80 photodetection events/subap./frame • 8-1 SNR • LGS • 1 Laser Guide Star • 2W dye laser Laser Development Meeting

4. MK LGS AO System parameters • AO = ALTAIR • Shack-Hartmann WFS • 12x12 subapertures • 500 Hz to 1 kHz frame rate • 310 to 800 photodetection events/subap./frame • 15-1 to 25-1 SNR • 0.04 to 0.08 arcsec tilt measurement accuracy • 0.05 to 0.1 mm rms WF through servo • LGS • 1 Laser Guide Star • High power laser (Spec. is 12 W equivalent CW laser) Laser Development Meeting

5. CP multi-LGS MCAO System parameters • MCAO • 2 to 3 DMs, 4 to 5 WFSs • 12x12 to 16x16 subapertures • 500 Hz to 1 kHz frame rate • 200 to 500 photodetection events/subap.(16x16)/frame • 10-1 to 20-1 SNR • 0.05 to 0.10 arcsec tilt measurement accuracy • 0.05 to 0.1 mm rms WF through servo • LGS • 4 to 5 Laser Guide Stars • High power lasers (Spec. similar to MK or somewhat lower) Laser Development Meeting

6. Laser systems requirements Laser Development Meeting

7. Laser systems power & beam quality requirements • CP LGS AO system (1) Simulation of 85 actuator curvature sensor performances with LGS (F. Rigaut’s AO modeling code) (2) Derive CW laser power requirement using J. Telle’s “slope efficiency” number (3) Compared the power requirement with Imperial College theoretical calculations & achieved experimental photon returns Laser Development Meeting

8. Laser systems power & beam quality requirements • MK LGS AO system (1) Simulation of 12x12 subap. Shack Hartmann WFS performances with LGS (F. Rigaut’s AO modeling code) for an ideal gaussian beam at zenith (2) Derive power requirements for different laser formats using J. Telle’s “slope efficiency” numbers (3) Multiply by coeff. 2 (resp. 3) to set the power requirements (resp. goal) while taking real laser beam and 45 degree elevation angle specification into account Laser Development Meeting

9. Laser systems power & beam quality requirements • CP multi-LGS MCAO system (1) Optimal estimator calculations with Brent Ellerbroek’s AO modeling code, using MTF-based approach to model LGS shape and WFS measurement accuracy (0 and 45 degree calculations, beam quality, lenslet and CCD degradations included) (2) Derive power requirements for different laser formats using J. Telle’s “slope efficiency” numbers Laser Development Meeting

10. Promising laser design approaches • Compact and potentially reliable sources like diode-pumped solid-state lasers and fiber lasers • Among them: • Sum-frequency solid state lasers • Thin disk laser (Nanolase, France – John Telle, SOR) • “Standard” Nd:YAG zig-zag slabs (Lincoln Lab, Tom Jeys – UoChicago, Ed. Kibblewhite & Lite Cycles, LLNL …) • Raman laser (UoArizona, Tom Roberts -…) • Raman fiber laser (Lite Cycles - IRE-POLUS Group, Germany) • And very likely others than we might not be aware of… Laser Development Meeting

11. Key physics and engineering issues • Sum frequency lasers: • heat management in the laser crystals (power limitation) and 1.32 mm laser (difficult to build) • Fiber lasers: • too wide a spectral bandwidth due to Brillouin scattering • General: • insufficient level of automation Laser Development Meeting

12. Gemini prospects for laser R&D • No R&D currently supported • Required development schedule • related to the MCAO laser systems delivery dates (June 2003) • R&D activities should start by the end of 2000 • R&D activities should focus on key components for operational high power lasers • Examples: 1.32 mm laser, sum-frequency mixing in non-linear crystals at high power levels, narrow-band fiber lasers, etc. Laser Development Meeting