Abstract 313

Submitted by Aurea GARCIA-RISSMANN

Authors

A. Garcia-Rissmann (1) & M. Le Louarn (2)

Affiliations

(1) Gemini Observatory, La Serena; (2) ESO, Garching

Abstract

We show the performances derived from simulations of a SCAO system for an ELT using a pyramid wavefront sensor (hereafter PYRWFS). The main objective of this work is to obtain the parameters that optimize the Strehl and characterize the system. Adopting K as the science band, we verify that the overall performance tends to be poorer as the sensing wavelength becomes shorter (as we probed K, H and R bands), the loop gain optimal range is dependent on the singular-value decomposition (SVD) truncation threshold used to build the command matrix, and that a "natural" modulation for the PYRWFS (i.e. zero modulation) produces in general poorer results when compared to modulated cases, being this especially true for the R-sensing band. Also more modulation is needed as one goes to shorter wavelengths. Comparisons between a scaled-down version of the simulations and those for a 42m telescope are performed. The atmospheric model adopted was always a von Karman with r0=0.13m (0.5um) and outer scale of 25m. The telescope pupil had a central obstruction of 28% and no spiders. The NGS was put on-axis, and diffraction between pyramid sub-pupils taken into account.