CCAT: characterizing the Fabry-Pérot interferometer mirrors and mount for the epoch of reionization spectrometer

The Epoch of Reionization Spectrometer (EoR-Spec) is an instrument module with unique spectroscopic capabilities within the Prime-Cam receiver on the Fred Young Submillimeter Telescope (FYST), a forthcoming six-meter aperture telescope to be situated on Cerro Chajnantor in the Atacama Desert, Chile. Engineered to investigate the processes of reionization and galaxy formation in the early universe, EoR-Spec employs line intensity mapping techniques to measure the [CII] fine-structure lines for the redshift range spanning from z=3.5 to 8. The module integrates a cryogenic scanning Fabry-Perot interferometer (FPI) to meet the spectral resolution criterion of approximately R=100. At the core of the FPI lie two parallel, identical highly reflective silicon-based mirrors, with a 14 cm aperture that form a resonating cavity, referred to as an etalon. These mirrors feature double-layer metamaterial anti-reflection coatings (ARC) on one side, complemented by metal mesh reflectors on the other. The double-layer ARC ensures minimal reflectance on the substrate surface and facilitates tailoring of the reflectance profile across the FPI bandwidth. The characterization of silicon mirrors and prototype testing are crucial steps in ensuring the optimal performance and functionality of the EoR-Spec instrument. Here we present an updated account of the ongoing efforts involved in the characterization of silicon mirrors and the mounting test conducted for the EoR-Spec instrument.