Sodium laser guide stars (LGSs) allow, in theory, full sky coverage, but have their own limitations. Variations of sodium layer altitude, thickness and atom density profile induce changing errors on wavefront measurements (LGS aberrations), especially with ELTs for which the LGS spot elongation is larger. In the framework of the Thirty-Meter-Telescope project (TMT), the AO-Lab of the University of Victoria (UVic) built a LGS-simulator test bed in order to assess the performance of new centroiding algorithms for LGS Shack-Hartmann wavefront sensors (SH-WFS). The principle of the LGS-bench is briefly reviewed. The closed-loop performances of the matched filter (MF) algorithm on laboratory 29x29 elongated spot images are presented and compared with the centre of gravity (CoG). The ability of the MF to track the LGS aberrations is successfully demonstrated. The UVic LGS-bench is not limited to SH-WFS and can serve as a LGS-simulator test bed to any other LGS-AO projects for which sodium layer fluctuations are an issue.

Date Published: 16 July 2008
PDF: 12 pages
Proc. SPIE 7015, Adaptive Optics Systems, 70154T (16 July 2008); doi: 10.1117/12.787470

Published in SPIE Proceedings Vol. 7015:
Adaptive Optics Systems
Norbert Hubin; Claire E. Max; Peter L. Wizinowich, Editor(s)