Development of Cryogenic Far-Infrared Fourier Transform Spectrometer with High Spectral Resolution

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Far-Infrared Fourier transform spectrometer should be operated at cryogenic temperature to avoid the thermal emission from itself. And the best way for far-infrared astronomy is the observation in space where is free from the atmospheric absorptions and emissions. The goal of this research is to develop the Fourier transform spectrometer with high spectral resolution under these unusual conditions.Since Fourier transform spectrometer is based on two beams interferometer, the precise displacement sensor is required to refer optical path difference. The displacement sensor for far-infrared Fourier transform spectrometer should be worked at cryogenic temperature. For example, required specification of a displacement sensor is 40 mm total displacement with a few micrometers accuracy. To achieve this requirement we adopt the optical scale with interferential scanning head. The commercial grade of this type of scale, of course, does not work under cryogenic temperature. We modify the part of the sensor head module and replace the sensor chips with cryogenic parts. Finally, we have developed the cryogenic displacement sensor for 40 mm displacement with 1 micrometer accuracy.We can take interferograms using our Fourier transform spectrometer with this displacement sensor at cryogenic temperature. The fundamental techniques to construct the cryogenic far-infrared Fourier transform spectrometer are established through this research.