High-contrast imager for Complex Aperture Telescopes (HiCAT): 1. Testbed design

摘要

Searching for nearby habitable worlds with direct imaging and spectroscopywill require a telescope large enough to provide angular resolution andsensitivity to planets around a significant sample of stars. Segmentedtelescopes are a compelling option to obtain such large apertures. However,these telescope designs have a complex geometry (central obstruction, supportstructures, segmentation) that makes high-contrast imaging more challenging. Weare developing a new high-contrast imaging testbed at STScI to provide anintegrated solution for wavefront control and starlight suppression on complexaperture geometries. We present our approach for the testbed optical design,which defines the surface requirements for each mirror to minimize theamplitude-induced errors from the propagation of out-of-pupil surfaces. Ourapproach guarantees that the testbed will not be limited by these Fresnelpropagation effects, but only by the aperture geometry. This approach involvesiterations between classical ray-tracing optical design optimization, andend-to-end Fresnel propagation with wavefront control (e.g. Electric FieldConjugation / Stroke Minimization). The construction of the testbed is plannedto start in late Fall 2013.