Physics – Optics
Scientific paper
Jul 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008spie.7015e.174r&link_type=abstract
Adaptive Optics Systems. Edited by Hubin, Norbert; Max, Claire E.; Wizinowich, Peter L. Proceedings of the SPIE, Volume 7015
Physics
Optics
Scientific paper
Exoplanet direct imaging with a ground-based telescope needs a very high performance adaptive optics (AO) system, so-called eXtreme AO (XAO), a coronagraph device, and a smart imaging process. One limitation of AO system in operation remains the Non Common Path Aberrations (NCPA). To achieve the ultimate XAO performance, these aberrations have to be measured with a dedicated wavefront sensor placed in the imaging camera focal plane, and then pre-compensated using the AO closed loop process. In any events, the pre-compensation should minimize the aberrations at the coronagraph focal plane mask. An efficient way for the NCPA measurement is the phase diversity technique. A pixel-wise approach is well-suited to estimate NCPA on large pupils and subsequent projection on the deformable mirror with Cartesian geometry. However it calls for a careful regularization for optimal results. The weight of the regularization is written in close-form for un-supervised tuning. The accuracy of NCPA pre-compensation is below 8 nm for a wide range of conditions. Point-by-point phase estimation improves the accuracy of the Phase Diversity method. The algorithm is validated in simulation and experimentally. It will be implemented in SAXO, the XAO system of the second generation VLT instrument: SPHERE.
Fusco Thierry
Mugnier Laurent
Robert Clélia
Sauvage Jean François
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