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Proceedings Paper

A "Fast and Furious'" solution to the low-wind effect for SPHERE at the VLT
Author(s): M. J. Wilby; C. U. Keller; J.-F. Sauvage; T. Fusco; D. Mouillet; J.-L. Beuzit; K. Dohlen
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Paper Abstract

We present a potential non-invasive solution to sensing the so-called low-wind effect (LWE) seen in the SPHERE instrument at the VLT, based on the "Fast and Furious (F&F) sequential phase diversity wavefront reconstruction algorithm. This uses non-coronagraphic focal-plane images available from the near-infra-red Differential Tip-Tilt Sensor (DTTS), with the closed-loop correction cycle itself providing the necessary phase diversity between frames required to reconstruct the full wavefront phase. Crucially, this means F&F does not need to apply large artificial phase probes as required by standard phase diversity algorithms, allowing it to operate in a real-time (∼10 Hz) correction mode without impacting science observations. In this paper we present the results of realistic closed-loop AO simulations designed to emulate SPHERE/DTTS observations of the LWE. With this we demonstrate that the F&F algorithm is capable of effective removal of the characteristic point-spread function (PSF) aberrations of strongly LWE-affected images within a few closed-loop iterations, with the final wavefront quality limited only by the corrective order of the deformable mirror. The ultimate goal of this project is to provide an independent, real-time and focal-plane wavefront sensor for SPHERE which is capable of detecting and directly compensating the LWE as it arises, thus improving coronagraph performance under the best 15–20 % of observing conditions where the effect is most pronounced.

Paper Details

Date Published: 27 July 2016
PDF: 12 pages
Proc. SPIE 9909, Adaptive Optics Systems V, 99096C (27 July 2016); doi: 10.1117/12.2233462
Show Author Affiliations
M. J. Wilby, Leiden Univ. (Netherlands)
C. U. Keller, Leiden Univ. (Netherlands)
J.-F. Sauvage, ONERA (France)
T. Fusco, ONERA (France)
D. Mouillet, Institut de Planétologie et d’Astrophysique de Grenoble (France)
J.-L. Beuzit, Institut de Planétologie et d’Astrophysique de Grenoble (France)
K. Dohlen, Lab. d'Astrophysique de Marseille (France)

Published in SPIE Proceedings Vol. 9909:
Adaptive Optics Systems V
Enrico Marchetti; Laird M. Close; Jean-Pierre Véran, Editor(s)

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