Impact of laser guide star fratricide on TMT MCAO system

Lianqi Wang; Angel Otarola; Brent Ellerbroek

doi:10.1117/12.857348

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14 July 2010 Impact of laser guide star fratricide on TMT MCAO system

Lianqi Wang, Angel Otarola, Brent Ellerbroek

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Proceedings Volume 7736, Adaptive Optics Systems II; 77360G (2010) https://doi.org/10.1117/12.857348
Event: SPIE Astronomical Telescopes + Instrumentation, 2010, San Diego, California, United States

Abstract

Laser beams projected from the ground to form laser guide stars (LGS) experience scattering and absorption that reduce their intensity as they propagate through the atmosphere. Some fraction of the scattered light will be collected by the other LGS wavefront sensors and causes additional background in parts of the pupil. This cross-talk is referred to as the fratricide effect. In this paper we quantify the magnitude of four different sources of scattering/absorption and back scattering, and evaluate their impact on performance with various zenith angles and turbulence profiles for the Thirty Meter Telescope (TMT) MCAO system, NFIRAOS. The resulting wavefront error is on the order of 5 to 20 nm RMS, provided that the mean background from the fratricide can be calibrated and subtracted with an accuracy of 80%. We have also found that the impact of fratricide is a weak function of LGS asterism radius.

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Lianqi Wang, Angel Otarola, and Brent Ellerbroek "Impact of laser guide star fratricide on TMT MCAO system", Proc. SPIE 7736, Adaptive Optics Systems II, 77360G (14 July 2010); https://doi.org/10.1117/12.857348

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