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Pyramid wave front sensor and laser guide stars for ELT

Abstract 149

Submitted by Brice LE ROUX


B. Le Roux




Adaptive optics for ELTs has to deal with several critical points. One of those is the wave front sensing and the nature of the reference stars. The use of laser guide stars appears today necessary and is planned for the E-ELT AO systems. If the Shack Hartmann behaviour with laser guide stars is relatively well known, and even optimized, it is not the case with other wave front sensors, as the pyramid WFS. A rational choice of WFS for AO on an ELT can therefore only be done after a benchmark of wave front sensors and their behaviour with a laser guide star. The wave front sensing measurement given by a pyramid WFS looking to a laser is still partially unknown. The behaviour of the pyramid when sensing the wave front on an extended object, its ability to deal with the laser elongation problem (which is, on the pyramid case, a z-axis oriented elongation) are still open questions. As an answer to those questions, which are critical for the choice of wave front sensors for AO on ELTs, we present simulation results made in the context and in the configuration of the EAGLE instrument (Multi-object adaptive optics system).