Analysis of on-sky sodium profile data and implications for LGS AO wavefront sensing

Sandrine J. Thomas; Donald Gavel; Sean Adkins; Bob Kibrick

doi:10.1117/12.789661

15 July 2008 Analysis of on-sky sodium profile data and implications for LGS AO wavefront sensing

Sandrine J. Thomas, Donald Gavel, Sean Adkins, Bob Kibrick

Proceedings Volume 7015, Adaptive Optics Systems; 70155L (2008) https://doi.org/10.1117/12.789661
Event: SPIE Astronomical Telescopes + Instrumentation, 2008, Marseille, France

Abstract

Astronomical adaptive optics (AO) systems are beginning to make extensive use of ~598 nm lasers projected onto the mesospheric sodium layer in order create artificial guide stars. This technique allows increased sky coverage with improved AO system performance. This approach is also dependent on the abundance and distribution of sodium atoms in the mesosphere and as a result present a unique set of difficulties not seen with natural stars. The sodium layer exhibits time dependent variations in density and altitude, and has a variable structure. The non-zero thickness and finite range of the sodium layer results in elongation of the LGS image due to perspective effects that are particularly significant for AO systems using Shack-Hartmann wavefront sensors (SHFWS) on extremely large telescopes (ELTs) such as the Thirty Meter Telescope (TMT). Both sodium layer variations and elongation will increase the error in the wavefront measurement. In order to understand these effects we have collected profiles of the sodium layer using off axis observations of a laser guide star at the Lick Observatory. In this paper, we will describe the analysis of these profiles and the implications of this analysis for the design of improved wavefront sensors (especially sampling, field of view) and SHWFS centroiding methods.

Citation Download Citation

Sandrine J. Thomas, Donald Gavel, Sean Adkins, and Bob Kibrick "Analysis of on-sky sodium profile data and implications for LGS AO wavefront sensing", Proc. SPIE 7015, Adaptive Optics Systems, 70155L (15 July 2008); https://doi.org/10.1117/12.789661

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