DESIGN AND PERFORMANCE OF CRYOGENIC, SCANNING FABRY-PEROT INTERFEROMETERS FOR THE LONG-WAVELENGTH SPECTROMETER ON THE INFRARED SPACE-OBSERVATORY

The design of cryogenic, scanning Fabry-Perot interferometers for the Long-Wavelength Spectrometer on the ESA Infrared Space Observatory is presented. The interferometers were designed to provide a spectral res olving power of 10(4) over the wavelength range 45-180 mu m, with the highest possible transmission efficiency consistent with this requirem ent. Metal meshes, custom designed with the aid of a theoretical model of metallic reflection, were used as the reflecting elements. The sca nning mechanism featured a spring-suspended plate, which was servocont rolled by moving coil actuators and monitored by capacitance micromete rs. The spectroscopic performance of the interferometers was measured in the laboratory and is compared with the model developed for the int erferometer design. Although the measured resolving powers were somewh at lower than expected because of the laboratory measurement condition s, the transmission efficiencies were in approximate agreement with th e design specification.