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 resolving power of 104 over the wavelength range 45–180 μm, with the highest possible transmission efficiency consistent with this requirement. Metal meshes, custom designed with the aid of a theoretical model of metallic reflection, were used as the reflecting elements. The scanning mechanism featured a spring-suspended plate, which was servocontrolled by moving coil actuators and monitored by capacitance micrometers. The spectroscopic performance of the interferometers was measured in the laboratory and is compared with the model developed for the interferometer design. Although the measured resolving powers were somewhat lower than expected because of the laboratory measurement conditions, the transmission efficiencies were in approximate agreement with the design specification