Optical alignment of the Roman Space Telescope’s Coronagraph Instrument

Optical alignment of the Coronagraph Instrument (CGI) was completed in time to begin its full-functional and environmental testing and its integration into the Roman Space Telescope (RST). CGI optics relay the optical pupil of the RST five times so that science operations can be conducted at internal pupil and image planes. The CGI has multiple active optical assemblies, including a fast-steering mirror, a focus-control mirror, two deformable mirrors, and six precision alignment mechanisms that articulate masks and apertures into the beam. Initial alignment of CGI optics was accomplished using an interferometer to measure the wavefront error as optics were added sequentially from back to front. The end-to-end wavefront error was initially verified using surrogate optics in place of active optical assemblies, to allow their simultaneous development. Throughout alignment, pupil and image planes were referenced and coaligned optically using fiducials. Upon alignment of the pupil-relay optics, the active optical assemblies were integrated and aligned, and the entire CGI alignment was then optimized. The CGI optical subsystem was mapped to fiducials, which will later be used to integrate CGI into the RST observatory. This manuscript details the many alignment steps required to successfully achieve the performance criteria of the CGI.