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Proceedings Paper

Development of an ELT XAO testbed using a Mach-Zehnder wavefront sensor: calibration of the deformable mirror
Author(s): Christian Delacroix; Maud P. Langlois; Magali Loupias; Eric Thiébaut; Louisa Adjali; Jonathan Leger; Michel Tallon
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Paper Abstract

Extreme adaptive optics (XAO) encounters severe difficulties to cope with the high speed (<1kHz), high accuracy and high order requirements for future extremely large telescopes. An innovative high order adaptive optics system using a self-referenced Mach-Zehnder wavefront sensor (MZWFS) allows counteracting these limitations. This sensor estimates very accurately the wavefront phase at small spatial scale by measuring intensity differences between two outputs, with a λ/4 path length difference between its two legs, but is limited in dynamic range due to phase ambiguity. During the past few years, such an XAO system has been studied by our team in the framework of 8-meter class telescopes. In this work, we report on our latest results with the XAO testbed recently installed in our lab, and dedicated to high contrast imaging with 30m-class telescopes (such as the E-ELT or the TMT). After reminding the principle of a MZWFS and describing the optical layout of our experiment, we will show the results of the assessment of the woofer-tweeter phase correctors, i.e., a Boston Micromachine continuous membrane deformable mirror (DM) and a Boulder Nonlinear Systems liquid crystal spatial light modulator (SLM). In particular, we will detail the calibration of the DM using Zygo interferometer metrology. Our method consists in the precise measurement of the membrane deformation while applying a constant deformation to 9 out of 140 actuators at the same time. By varying the poke voltage across the DM operating range, we propose a simple but efficient way of modeling the DM influence function using a Gaussian model. Finally, we show the DM flattening on the MZWFS allowing to compensate for low order aberrations. This work is carried out in synergy with the validation of fast iterative wavefront reconstruction algorithms, and the optimal treatment of phase ambiguities in order to mitigate the dynamical range limitation of such an MZWFS.

Paper Details

Date Published: 14 September 2015
PDF: 9 pages
Proc. SPIE 9617, Unconventional Imaging and Wavefront Sensing 2015, 96170G (14 September 2015); doi: 10.1117/12.2189094
Show Author Affiliations
Christian Delacroix, Ctr. de Recherche Astrophysique de Lyon, CNRS (France)
Maud P. Langlois, Ctr. de Recherche Astrophysique de Lyon, CNRS (France)
Magali Loupias, Ctr. de Recherche Astrophysique de Lyon, CNRS (France)
Eric Thiébaut, Ctr. de Recherche Astrophysique de Lyon, CNRS (France)
Louisa Adjali, Ctr. de Recherche Astrophysique de Lyon, CNRS (France)
Jonathan Leger, Ctr. de Recherche Astrophysique de Lyon, CNRS (France)
Michel Tallon, Ctr. de Recherche Astrophysique de Lyon, CNRS (France)

Published in SPIE Proceedings Vol. 9617:
Unconventional Imaging and Wavefront Sensing 2015
Jean J. Dolne; Thomas J. Karr; Victor L. Gamiz, Editor(s)

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