Extreme Wave Front Sensing Accuracy for the Eclipse Coronagraphic Space Telescope

摘要

The Eclipse coronagraphic telescope will allow for high contrast imaging near a target star to facilitate planet finding. One key element will be its high accuracy, high authority deformable mirror (DM) that controls the wave front error (WFE) down to an acceptable level. In fact, to achieve the desired contrast ratio of nine orders of magnitude (in intensity) to within 0.35 arcseconds of the target star, the WFE in the telescope must be controlled to level below 1A rms within the controllable bandwidth of the DM. To achieve this extreme wave front sensing (WFS) accuracy, we employ a focus-diverse phase retrieval method extended from the Next Generation Space Telescope baseline approach. This method processes a collection defocused point-spread functions, measured at the occulting position in the Eclipse optical system, into a high accuracy estimate of the exit-pupil WFE. Through both simulation and hardware experiments, we examine and establish the key data requirements, such as the defocus levels and imaging signal-to noise level, that are necessary to obtain the desired WFS accuracy and bandwidth.