Cryogenic Michelson Interferometer Spectrometer For Space Shuttle Application

A Michelson interferometer spectrometer using a flexural pivot suspension for the moving mirror was fabricated for use at 20° K as part of the CIRRIS 1A experiment. The spectral range 2.5 to 25 μm is achieved using a potassium bromide beamsplitter. The softness of the beamsplitter material required special mounting care to preserve beamsplitter flatness while undergoing the strain of being cooled and the shock and vibration of the shuttle launch. Five various sized elements in the arsenic-doped-silicon focal plane provide for tradeoff of sensitivity, spatial and spectral resolution capabilities. A redundant position reference system uses optical fibers to couple optical power from HeNe lasers through the vacuum/cryogenic interface into the interferometer optics where it travels antiparallel to the infrared signal. An alignment system using geared stepper motors provides capability of realignment in space. An eight-position filter wheel is used to enhance the out-of-band signal rejection to enhance high sensitivity in the presence of strong infrared emitters. The interferometer is mounted inside of a high-off-axis rejection telescope to enable measurement of the earth limb emissions. The telescope is cooled to 20° K using supercritical liquid helium.