A high-finesse broadband optical cavity using calcium fluoride prism retroreflectors

A high-finesse broadband optical cavity has been developed for use in the ultraviolet and visible region using Brewster-angle calcium fluoride (CaF₂) prism retroreflectors. Prior to prism construction, optical loss measurements of CaF₂ windows were performed using cavity ring-down spectroscopy at 250 nm. Total optical loss showed high spatial correlation with crystal birefringence, which was partially mitigated by orienting the <111> crystal axis with the laser beam. Prism reflectivity was measured using cavity ring-down spectroscopy and found to be 99.77% at 250 nm and 99.96% at 500 nm, allowing for relatively high-finesse operation over hundreds of nm bandwidth with a single cavity.