Compatibility of a Diffractive Pupil and Coronagraphic Imaging

Abstract

ABSTRACTDetection and characterization of exo-Earths require direct imaging techniques that can deliver contrast ratios of 1010 at 100 mas or smaller angular separation. At the same time, astrometric data is required to measure planet masses and to help detect planets and constrain their orbital parameters. To minimize costs, a single space mission can be designed using a high-efficiency coronagraph to perform direct imaging and a diffractive pupil to calibrate wide field distortions to enable high-precision astrometric measurements. This article reports the testing of a diffractive pupil on the high-contrast test bed at the NASA Ames Research Center to assess the compatibility of using a diffractive pupil with coronagraphic imaging systems. No diffractive contamination was found within our detectability limit of 2 × 10-7 contrast outside a region of 12 λ/D and 2.5 × 10-6 within a region spanning from 2 to 12 λ/D. Morphology of the image features suggests that no contamination exists even beyond the detectability limit specified or at smaller working angles. In the case that diffractive contamination is found beyond these stated levels, active wavefront control would be able to mitigate its intensity to 10-7 or better contrast.