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Guidestar Laser Requirements for ELTs

Brent Ellerbroek(with thanks to Norbert Hubin and Michael Lloyd-Hart)

2007 CfAO Fall RetreatLake Arrowhead

November 2, 2007

TMT.AOS.PRE.07.xxx.REL01

TMT.AOS.PRE.07.040.REL01The information contained herein is subject to the restrictions contained on the cover page of this document. 2

Early Light Laser Requirements Summary

Project E-ELT GMT TMT

Early light LGS AO modes LTAO, GLAO LTAO, GLAO MCAO

(Follow-on LGS AO modes) MCAO, MOAO

MCAO, MOAO

GLAO, MOAO

RMS WFE, nm ~220 ~200 ~190

Subap. width, cm 50 50 50

Frame rate, Hz 1000 1000 800

# of LGS 6 6 6

CW LGS power estim. , W 40 (baseline) 30 (baseline) 25 (baseline)

Pulsed LGS power estim., W 15-20 10-12? 10-12

Laser Mass/Volume Constraints

? Dedicated room 7x2x2m

3x Gemini-South laser

Changing g vector? yes no yes

TMT.AOS.PRE.07.040.REL01The information contained herein is subject to the restrictions contained on the cover page of this document. 3

Goals and Upgrade Paths

Goals– Pulsed lasers

Dynamic refocusingRayleigh backscatter gatingBoth?

– Compatible with fiber beam transport– As small and as light as possible

Upgrade Paths– Higher powers (e.g., 4-5x) for reduced RMS WFE– Additional guidestars for MOAO and enlarged FoVs