Focal plane complex wavefront sensing with coronagraphic phase diversity on the THD2 bench

Abstract : The final performance of current and future instruments dedicated to exoplanet detection and characterization is limited by intensity residuals in the scientific image plane, which mainly originate in uncorrected optical aberrations. In order to reach high contrasts, these aberrations needs to be compensated for. We have proposed a focal-plane wave-font sensor called COFFEE (for COronagraphic Focal-plane wave-Front Estimation for Exoplanet detection), which consists in an extension of conventional phase diversity to a coronagraphic system. We have recently shown that COFFEE could be extended to jointly estimate both phase and amplitude of the complex field in a pupil plane, which is mandatory in the context of very high contrast space-based coronagraphic instruments, e.g. for exo-Earth imaging. In this communication, we perform the first experimental validation of the estimation of the complex field with COFFEE, on a high-contrast imaging bench representative of a coronagraphic space instrument, namely the THD2 bench of LESIA/Observatoire de Paris. We first calibrate precisely the diversity that is effectively introduced by the pupil-plane deformable mirror (DM) by using classical (i.e., non coronagraphic) phase diversity, which is actually relatively far from a pure defocus due to the DM nonlinearities. Then, we introduce either phase aberrations using the pupil-plane DM or amplitude aberrations using the out-of-pupil-plane DM, we measure several coronagraphic images with varying diversity, and we reconstruct the complex wavefront from these images. We show that COFFEE is able to distinguish between amplitude and phase aberrations and we assess the measurement precision. A short-term perspective is to close the loop using these measurements in order to perform a dark-hole in the focal plane.
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Olivier Herscovici-Schiller, Laurent M. Mugnier, Pierre Baudoz, Raphaël Galicher, Jean-Francois Sauvage, et al.. Focal plane complex wavefront sensing with coronagraphic phase diversity on the THD2 bench. AO4ELT, Jun 2017, Puerto de la Cruz, Spain. ⟨hal-01994363⟩



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