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Design and development 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 can not be transported to NIST for calibration. When used inside the MDXR, the Cryo-FTS is expected to be able to provide relative spectral measurements with an accuracy of < 0.3 % uncertainty of infrared sources with a spectral range from 4 μm to 15 μm and a spectral resolution of 0.6 cm-1. The Cryo-FTS spectral range is determined by the beamsplitter since all of its other optics use reflective materials. 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 μrad). The interferometer uses flat metal mirrors and KBr flat optics and maintains low wavefront distortion for infrared beams of up to 1.63 cm diameter. 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 based metrology system. The interferometer is expected to provide modulation efficiency of better than 22% with limited power dissipation (< 2.8 W) during continuous operation.