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Cryogenic Fourier transform spectrometer for infrared spectral calibrations from 4 to 20 micrometers

We present initial performance data from a cryogenic Fourier transform spectrometer (Cryo-FTS) designed for lowbackground spectral infrared calibrations. The Cryo-FTS operates at a temperature of approximately 15 K and has been integrated into an infrared transfer radiometer containing a calibrated Si:As blocked impurity band (BIB) detector. Because of its low operating temperature, the spectrometer exhibits negligible thermal background signal and low drift. Data from tests of basic spectrometer function, such as modulation efficiency, scan jitter, spectral range, spectral resolution and sweep speed will be presented. We will also discuss calibration techniques and results pertinent to operation of the Cryo-FTS as part of a calibration instrument, including background, signal offset and gain, and spectral noise equivalent power. The spectrometer is presently limited to wavelengths below 25 micrometers but can be in principle extended to longer wavelengths by replacing its KBr beamsplitter with another beamsplitter engineered for use beyond 25 micrometers.