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Corresponding Author
Name
Francois Rigaut
Authors
NameAffiliation
Damien Gratadour Gemini Observatory
Matthieu Bec Gemini Observatory
Abstract
Session2 (Adaptive optics, interferometry, and other approaches to mitigate atmospheric optical turbulence.)
Title'Real-time sodium layer thickness monitoring with the Altair Laser Guide Star System'
AbstractWhile quad-cell photon counting wavefront sensors used in many astronomical adaptive optics (AO) systems allow to detect weaker sources thanks to a lower or non-existent read-out noise, the limited field of view as well as the undersampling of the spot lead to severe non-linearity issues. A quad-cell usually requires the use of the so-called centroid gains, factors that translate the intensity ratio into a physical value for the spot displacement. The value of these gains is related to the spot extent, i.e. the natural seeing and the spot elongation in the case of Laser Guide Star (LGS AO). We present a novel method for optimizing these centroid gains during the observations that allows us to estimate the best gains to apply in real-time and offers an estimate of the local sodium layer thickness as a by-product. To assess the validity of the method, we present a series of measurements acquired during few nights of Altair LGS commissioning that shows that the estimated centroid gain values are correlated to the seeing values while they are not correlated to the estimated sodium layer thickness.

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Updated on: Wed, Dec 17 2014 - 1849 UTC
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