Sensing Quasi-Static Aberrations of Adaptive Optics Systems On-Line with Long-Exposure Phase Diversity

¹ Office National d’Etudes et de Recherches Aerospatiales (ONERA), Optics Department, BP 72, F-92322 Chatillon cedex, France
² Groupement d’Interet Scientifique PHASE (Partenariat Haute resolution Angulaire Sol Espace) between ONERA, Observatoire de Paris, CNRS and Universite Paris Diderot
³ LESIA, Observatoire de Paris, 5 place Jules Janssen, 92195 Meudon, France.

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Abstract

We validate by simulations an extension of the phase diversity technique that uses long exposure adaptive optics corrected images for sensing quasi-static aberrations during the scientific observation, in particul ar for high-contrast imaging. The principle of the method is that, for a sufficiently long exposure time, the residual turbulence is averaged into a convolutive component of the image and that phase diversity estimates the sole static aberrations of interest. The advantages of such a pro cedure, compared to the processing of short- exposure image pairs, are that the separation between static aberrat ions and turbulence-induced ones is performed by the long-exposure itself and not numerically, that only one image pair must be processed, that the estimation benefits from the high SNR of long-exposure images, and that only the static aberrations of interest are to be estimated. Long-exposure phase diversity can also be used as a phasing sensor for a segmented aperture telescope. Thus, it may be particularly useful for future planet finder projects such as EPICS on the European ELT.