Dec. 7, 1999Laser Development Meeting1 Laser Requirements and Prospects for Gemini AO Program Céline d’Orgeville Gemini Laser Systems Engineer

Dec. 7, 1999Laser Development Meeting2 Gemini AO program NORTH SOUTH Altair w/ NGS Altair w/ LGS Hokupa’a W LGS CP Hokupa’a 85 CP Multi-LGS MCAO CP Multi-LGS MCAO

Dec. 7, 1999Laser Development Meeting3 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

Dec. 7, 1999Laser Development Meeting4 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  m rms WF through servo LGS –1 Laser Guide Star –High power laser (Spec. is 12 W equivalent CW laser)

Dec. 7, 1999Laser Development Meeting5 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  m rms WF through servo LGS –4 to 5 Laser Guide Stars –High power lasers (Spec. similar to MK or somewhat lower)

Dec. 7, 1999Laser Development Meeting6 Laser systems requirements

Dec. 7, 1999Laser Development Meeting7 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

Dec. 7, 1999Laser Development Meeting8 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

Dec. 7, 1999Laser Development Meeting9 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

Dec. 7, 1999Laser Development Meeting10 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…

Dec. 7, 1999Laser Development Meeting11 Key physics and engineering issues Sum frequency lasers: –heat management in the laser crystals (power limitation) and 1.32  m laser (difficult to build) Fiber lasers: –too wide a spectral bandwidth due to Brillouin scattering General: –insufficient level of automation

Dec. 7, 1999Laser Development Meeting12 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  m laser, sum-frequency mixing in non- linear crystals at high power levels, narrow-band fiber lasers, etc.

Dec. 7, 1999Laser Development Meeting13 MCAO Strehl vs. LGS signal

Dec. 7, 1999Laser Development Meeting14 MCAO Strehl vs. off-axis angle