Phase correction of segment diffraction for high-contrast imaging
Laurent Puyeo, Bruce Macintosh, Remi Soummer, Mitchell Troy
The exquisite angular resolution of segmented extremely large telescopes will provide astronomers with unique science opportunities in exoplanet imaging, from the ability to characterize the birth of exoplanets in star-forming regions to the direct detection of mature exoplanets in reflected light. However segmented apertures complicate the design of coronagraphic solutions for these instruments. While fill factor is a crucial figure of merit, e.g. many small segments with small gaps greatly simplify coronagraphic designs compared to a few large segments with large gaps, the static contrast is ultimately limited by optical artifacts due to the image of the segments gaps leaking through the starlight suppression system. Recent developments have shown how to accommodate segmented geometries using tailored coronagraphic designs (such as the generalized APLC and double stage Optical Vector Vortex Coronagraph). The successful implementation of such solutions at the very high contrast level can potentially degrade throughput and render the whole starlight suppression system more sensitive to both manufacturing and segments phasing errors. In this paper we propose an alternative solution that treats segment gaps can as a special case in reflectivity errors, with favorable spatial frequency properties but very high amplitude. Such reflectivity errors will have to be controlled in even a monolithic high-contrast system. We present the results of a numerical study which includes two sequential deformable mirrors as an extra degree of freedom in the design of the coronagraphic solution.