PIAA coronagraph design for the Exo-C Mission concept

Abstract

The Exoplanet Coronagraph (Exo-C) mission concept consists of a 1.4m space telescope equipped with a high performance coronagraph to directly image exoplanets and disks around many nearby stars. One of the coronagraphs under consideration to be used for this mission is the highly efficient Phase-Induced Amplitude Apodization (PIAA) coronagraph. This paper presents and describes: (a) the PIAA design for Exo-C; (b) an end-to-end performance analysis including sensitivity to jitter, and (c) the expected science yield of Exo-C with PIAA. The design is a “classic” PIAA, which is made possible by the unobstructed aperture. It consists of a pair of forward and inverse PIAA optics and a simple hard-edge focal plane mask. A mild binary pre-apodizer relaxes the radius of curvature on the PIAA mirrors to be easier than typical PIAA mirrors manufactured to date. This design has been optimized for high performance while being relatively insensitive to low order aberrations. The throughput is 90% relative to telescope PSF, while the inner working angle is 2.1 l/D and the contrast is ~1e-9 in a full 360-degree field of view (after wavefront control with two DMs), all for a 20% spectral band centered around 550nm. The design also has good tolerance to jitter: contrast at 1.6mas jitter is still within a factor of a few of 1e-9.