Performance of a Cryogenic Michelson Interferometer

A cryogenic Fourier transform infrared spectrometer (Cryo-FTS) was developed for the Low Background Infrared (LBIR) facility at the National Institute of Standards and Technology (NIST). This spectrometer was developed for the Missile Defense Agency Transfer Radiometer (MDXR) that will be used to calibrate infrared sources that cannot be transported to NIST for calibration. When used inside the MDXR, the Cryo-FTS provides relative spectral measurements with a repeatability better than 1% over the spectral range from 3 mu m to 15 mu m and at a spectral resolution of 0.6 cm(-1). This level of performance is enabled by the use of an advancec real-time resampling method. The compact interferometer uses a compensated Michelson configuration and has an operating temperature range between 10 K and 340 K with very low static beam redirection (< 215 mu rad). The interferometer uses flat mirrors and a KBr beamsplitter and compensator. This optics maintains low wavefront distortion for infrared beams of up to 2 cm diameter and 5 mrad divergence. It integrates a digitally servo-controlled porchswing mechanism to provide an accurate and repeatable optical path difference and is supported by a Wavefront Alignment (WA) system to correct for wavefront residual tilt in real time using a fibre optic coupled metrology system. The interferometer provides modulation efficiency of better than 44% with limited power dissipation (< 2.8 W) during operation.