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Initial alignment of the CGI optics was completed in the reverse direction, using a commercial dynamic Twyman-Green interferometer to measure the wavefront error through each relay as optics were added sequentially from back to front. The end-to-end wavefront error was initially verified using surrogate optics in place of the active optical assemblies, to allow their simultaneous development and test. Throughout alignment, pupil and image planes were referenced and coaligned optically using fiducials, including spherically mounted retroreflectors (SMRs) that were positioned by a laser tracker and measured by the interferometer camera. Upon end-to-end alignment of the pupil-relay optics, the active optical assemblies were integrated and aligned individually, and the entire CGI alignment was then optimized. The CGI optical subsystem was also mapped to SMR fiducials, which will later be used to integrate CGI into the RST observatory and verify its alignment to the Telescope’s line of sight. This paper details the many alignment steps required to successfully achieve the performance criteria of the CGI. |
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