Implementation of a dark zone maintenance algorithm for speckle drift correction in a high contrast space coronagraph
Résumé
Due to the limited number of photons, directly imaging planets requires long integration times with a coronagraphic instrument. The wavefront must be stable on the same time scale, which is often difficult in space due to time-varying wavefront errors from thermal gradients and other mechanical instabilities. We discuss a laboratory demonstration of a photon-efficient dark zone maintenance (DZM) algorithm in the presence of representative wavefront error drifts. The DZM algorithm allows for simultaneous estimation and control while obtaining science images and removes the necessity of slewing to a reference star to regenerate the dark zone mid-observation of a target. The experiments are performed on the high-contrast imager for complex aperture telescopes at the Space Telescope Science Institute. The testbed contains an IrisAO segmented primary surrogate, a pair of continuous Boston Micromachine (BMC) kilo deformable mirrors (DMs), and a Lyot coronagraph. Both types of DMs are used to inject synthetic high-order wavefront aberration drifts into the system, possibly similar to those that would occur on telescope optics in a space observatory, which are then corrected by the BMC DMs via the DZM algorithm. In the presence of BMC, IrisAO, and all DM wavefront error drift, we demonstrate maintenance of the dark zone contrast (5.8 − 9.8 λ / Dlyot) at monochromatic levels of 8.5 × 10 − 8, 2.5 × 10 − 8, and 5.9 × 10 − 8, respectively. In addition, we show multiwavelength maintenance at a contrast of 7.0 × 10 − 7 over a 3% band centered at 650 nm (BMC drift). We demonstrate the potential of adaptive wavefront maintenance methods for future exoplanet imaging missions, and our demonstration significantly advances their readiness.