We report on experimental stabilization of low-order aberrations on a high-contrast testbed for exoplanet imaging, in up to 10% broadband light under natural and artificial drifts. The measurements are performed with a Zernike wavefront sensor using the light rejected by the focal plane mask of an apodized Lyot coronagraph. We conduct the experiments on the High-contrast imager for Complex Aperture Telescopes testbed, with a segmented aperture and two continuous deformable mirrors. We study several use cases, from the stabilization of a pre-established dark hole to the concurrent combination with focal-plane wavefront sensing in the form of sequential pairwise sensing over several wavelengths.
We present recent laboratory results demonstrating high-contrast coronagraphy for the future space-based large IR/Optical/Ultraviolet telescope recommended by the Decadal Survey. The High-contrast Imager for Complex Aperture Telescopes (HiCAT) testbed aims to implement a system-level hardware demonstration for segmented aperture coronagraphs with wavefront control. The telescope hardware simulator employs a segmented deformable mirror with 37 hexagonal segments that can be controlled in piston, tip, and tilt. In addition, two continuous deformable mirrors are used for high-order wavefront sensing and control. The low-order sensing subsystem includes a dedicated tip-tilt stage, a coronagraphic target acquisition camera, and a Zernike wavefront sensor that is used to measure and correct low-order aberration drifts. We explore the performance of a segmented aperture coronagraph both in “static” operations (limited by natural drifts and instabilities) and in “dynamic” operations (in the presence of artificial wavefront drifts added to the deformable mirrors), and discuss the estimation and control strategies used to reach and maintain the dark-zone contrast using our low-order wavefront sensing and control. We summarize experimental results that quantify the performance of the testbed in terms of contrast, inner/outer working angle and bandpass, and analyze limiting factors.
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