Cryogenic tunable near-infrared Fabry Perot interferometer for Next Generation Space Telescope

An engineering test unit Fabry-Perot interferometer has been designed and built to operate in the 1.5-1.7 um regime from room temperature to 30 K°. The Fabry-Perot interferometer is tuned by controlling the gap spacing between the two highly reflecting mirrors. Capacitance sensors are used to control the gap spacing and maintain parallelism of the mirrors. An overview of the optical, mechanical, electrical, and control designs of the instrument are described. Some early results at cryogenic temperature indicative of the performance of the instruments are presented.