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Comparison of centroiding algorithms to optimize Shack Hartmann WFS in the context of ELTs

Abstract 141

Submitted by Sandrine THOMAS


S. Thomas, D. Gavel, R. Conan, O. Lardiere, S. Adkins


UCO/Lick Observatory; University of Victoria; Keck Observatory


Along with the expected ELTs comes the diversification of Adaptive Optics (AO) systems. Most of these foreseen AO systems will make extensive use of laser guide stars (LGS) in order to increase the sky coverage. The bright LGS beacon is expected to reduce the wavefront measurement errors and to improve the performance. However, because of the larger diameter of the next generation of telescopes, the LGS elongation seen in a Shack-Hartmann Wavefront Sensor is larger, i.e up to 7" for a 30m telescope. With such an elongation, both photon and read-out noise will increase and the density fluctuations of sodium atoms in the sodium layer start to matter. In this paper, we conduct Shack-Hartmann simulations using real sodium profiles taken at the Lick Observatory. We are comparing two methods of centroiders: the matched filter and the correlation. The results from simulations are then discussed with respect to results obtained at the UVic LGS test bench and in the particular case of the NFIRAOS AO system for TMT. The goal is to better understand the impact of LGS-induced aberrations on the final error budget for Shack- Hartmann WFSs.

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