Dec. 7, 1999 Laser Development Meeting 1

Laser Requirements and Laser Requirements and ProspectsProspects

for Gemini AO Programfor Gemini AO Program

Céline d’OrgevilleGemini Laser Systems Engineer

Dec. 7, 1999 Laser Development Meeting 2

Gemini AO programGemini AO program

NORTH

SOUTH

1999

2000

2001

2002

2003

2004

Altair w/ NGSAltair w/ NGSAltair w/ LGSAltair w/ LGS

Hokupa’aHokupa’a 3636 8585

2W LGS2W LGSCP Hokupa’aCP Hokupa’a 8585

CP Multi-LGS MCAOCP Multi-LGS MCAO

Dec. 7, 1999 Laser Development Meeting 3

CP LGS AO System CP LGS AO System parametersparameters

• 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, 1999 Laser Development Meeting 4

MK LGS AO System MK LGS AO System parametersparameters

• 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, 1999 Laser Development Meeting 5

CP multi-LGS MCAO System CP multi-LGS MCAO System parametersparameters

• 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, 1999 Laser Development Meeting 6

Laser systems requirementsLaser systems requirements

Laser requirements CP LGS AO MK LGS AO CP multi-LGS MCAO

Average power2 W CW laserGoal: 3W CW laser

12 W equiv. CW laserGoal: 18 W equiv. CW laser

< 5x 12 W equiv. CW laser

Beam quality < 1.5 DL1

ReliabilityMTBF (critical) > 900 h of operationMTBF (minor) > 100 h of operation

Staffing 1 laser specialist + 2 laser technicians for both MK and CP

Laser delivery Oct. 2000 Jan. 2001 June 2003

System operation Aug. 2001 Jan. 2002 March 2004

Observation use Once every other night (12 hours)

1 DL = Diffraction Limited2 MTBF = Mean Time Between Failure

Dec. 7, 1999 Laser Development Meeting 7

Laser systems power & Laser systems power & beam quality requirementsbeam 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, 1999 Laser Development Meeting 8

Laser systems power & Laser systems power & beam quality requirementsbeam 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, 1999 Laser Development Meeting 9

Laser systems power & Laser systems power & beam quality requirementsbeam 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, 1999 Laser Development Meeting 10

Promising laser design Promising laser design approachesapproaches

• 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, 1999 Laser Development Meeting 11

Key physics and Key physics and engineering issuesengineering 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, 1999 Laser Development Meeting 12

Gemini prospects for laser Gemini prospects for laser R&DR&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.