1Princeton Univ. (United States) 2Univ. of San Francisco (United States) 3Massachusetts Institute of Technology (United States) 4Space Telescope Science Institute (United States) 5DOTA, ONERA, Univ. Paris Saclay (France) 6Aix Marseille Univ., CNRS, LAM (France) 7Univ. of Rochester (United States) 8Univ. of California, Santa Cruz (United States)
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Due to the limited number of photons, directly imaging planets requires long integration times. The wavefront must be stable on the same time scale which is often difficult in space due to thermal variations and vibrations. In this paper, we discuss the results of implementing a dark hole maintenance (DHM) algorithm (Pogorelyuk et. al. 2019)1 on the High-contrast imager for Complex Aperture Telescopes (HiCAT) at the Space Telescope Science Institute (STScI). The testbed contains a pair of deformable mirrors (DMs) and a lyot coronagraph. The algorithm uses an Extended Kalman Filter (EKF) and DM dithering to predict the drifting electric field in the dark hole along with Electric Field Conjugation to cancel out the drift. The DM dither introduces phase diversity which ensures the EKF converges to the correct value. The DHM algorithm maintains an initial contrast of 8.5 x 10-8 for 6 hrs in the presence of the DM actuator random walk drift with a standard deviation of 1:7 x 10-3 nm/s..
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Susan M. Redmond, N. Jeremy Kasdin, Leonid Pogorelyuk, Remi Soummer, Laurent Pueyo, Marshall D. Perrin, Matthew Maclay, James Noss, Iva Laginja, Scott D. Will, Julia Fowler, "Implementation of a dark hole maintenance algorithm for speckle drift in a high contrast space coronagraph," Proc. SPIE 11443, Space Telescopes and Instrumentation 2020: Optical, Infrared, and Millimeter Wave, 114432K (15 December 2020); https://doi.org/10.1117/12.2561488