Residual Wave Front Phase Estimation in the Reimaged Lyot Plane for the Eclipse Coronagraphic Telescope

摘要

Coronagraphs for extra-solar planet detection remove diffracted stellar light through the combination of a coronagraphic mask and a Lyot stop. When the entrance pupil contains a nearly perfect wave front, most of the stellar light is absorbed at the mask. Light scattered around the spot due to mid- and high-spatial frequency phase errors in the pupil appears at the Lyot plane as speckles whose amplitudes are proportional to the local wave front phase residuals. The speckles scale with optical wavelength but are not radially smeared. The Eclipse deformable mirror (DM) can be used to modify the Lyot amplitude distribution, providing a simple means of estimating the residual phase content and controlling the wave front. To reduce the detrimental noise carried by uncontrollable high-spatial frequency wave front components, the Lyot plane signal is filtered at the science plane to pass only the controllable spatial frequencies that contribute to the dark hole. The Lyot stop is then reimaged onto a detector. We demonstrate through simulations that this approach significantly improves the signal-to-noise ratio of the planet measurement.