Overview of focal plane wavefront sensors to correct for the Low Wind Effect on SUBARU/SCExAO

Sebastien Vievard; Steven Bos; Frederic Cassaing; Alban Ceau; Olivier Guyon; Nemanja Jovanovic; Christoph U. Keller; Julien Lozi; Frantz Martinache; Aurelie Montmerle-Bonnefois; Laurent Mugnier; Mamadou NDiaye; Barnaby Norris; Ananya Sahoo; Jean-Francois Sauvage; Frans Snik; Michael J. Wilby; Alisson Wong

arXiv · 1912.10179

Overview of focal plane wavefront sensors to correct for the Low Wind Effect on SUBARU/SCExAO

Sebastien Vievard·Steven Bos·Frederic Cassaing·Alban Ceau·Olivier Guyon·Nemanja Jovanovic·Christoph U. Keller·Julien Lozi·Frantz Martinache·Aurelie Montmerle-Bonnefois·Laurent Mugnier·Mamadou NDiaye·Barnaby Norris·Ananya Sahoo·Jean-Francois Sauvage·Frans Snik·Michael J. Wilby·Alisson Wong

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Abstract

The Low Wind Effect (LWE) refers to a phenomenon that occurs when the wind speed inside a telescope dome drops below $3$m/s creating a temperature gradient near the telescope spider. This produces phase discontinuities in the pupil plane that are not detected by traditional Adaptive Optics (AO) systems such as the pyramid wavefront sensor or the Shack-Hartmann. Considering the pupil as divided in 4 quadrants by regular spiders, the phase discontinuities correspond to piston, tip and tilt aberrations in each quadrant of the pupil. Uncorrected, it strongly decreases the ability of high contrast imaging instruments utilizing coronagraphy to detect exoplanets at small angular separations. Multiple focal plane wavefront sensors are currently being developed and tested on the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument at Subaru Telescope: Among them, the Zernike Asymmetric Pupil (ZAP) wavefront sensor already showed on-sky that it could measure the LWE induced aberrations in focal plane images. The Fast and Furious algorithm, using previous deformable mirror commands as temporal phase diversity, showed in simulations its efficiency to improve the wavefront quality in the presence of LWE. A Neural Network algorithm trained with SCExAO telemetry showed promising PSF prediction on-sky. The Linearized Analytic Phase Diversity (LAPD) algorithm is a solution for multi-aperture cophasing and is studied to correct for the LWE aberrations by considering the Subaru Telescope as a 4 sub-aperture instrument. We present the different algorithms, show the latest results and compare their implementation on SCExAO/SUBARU as real-time wavefront sensors for the LWE compensation.

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Sebastien Vievard, Steven Bos, Frederic Cassaing, Alban Ceau, Olivier Guyon, Nemanja Jovanovic, Christoph U. Keller, Julien Lozi, Frantz Martinache, Aurelie Montmerle-Bonnefois, Laurent Mugnier, Mamadou NDiaye, Barnaby Norris, Ananya Sahoo, Jean-Francois Sauvage, Frans Snik, Michael J. Wilby, Alisson Wong. 2019-12-21. Overview of focal plane wavefront sensors to correct for the Low Wind Effect on SUBARU/SCExAO. https://arxiv.org/abs/1912.10179

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