Coronagraph verification stimulus and its application to validate the Roman Space Telescope Coronagraph Instrument

The coronagraph instrument (CGI) for NASA's Nancy Grace Roman Space Telescope is capable of detecting visible light from planets orbiting nearby stars and measuring its spectrum. To verify that the coronagraph met all of its functionality and performance requirements, we needed an optical source that mimics the collimated starlight beam from Roman's Optical Telescope Assembly (OTA), with sufficient stability to test the coronagraph's performance requirements and flight-like operations in a flight-like environment. The coronagraph verification stimulus (CVS) is the instrument designed for this purpose. It consists of an optical bench mounted rigidly on a support structure, perching over the top of the coronagraph, and mounted to the same posts that hold the coronagraph. The light source is an NKT Super-K supercontinuum laser delivering light to the backside of a high-precision pinhole via a photonic crystal fiber output. The CVS optics collimate the pinhole output, and a transmitting mask sets the beam size and obscuration profile to match the predicted dimensions of the beam from the flight OTA. The pupil mask is imaged on a PI tip-tilt "jitter mirror," and the beam is then relayed through a two-mirror periscope to deliver the beam on the CGI's entrance pupil. CVS met its design requirements, it was installed and aligned on top of CGI and provided light to successfully perform the in-air and vacuum test sequences used to validate CGI.