Design and end-to-end validation of a cryogenic far-infrared post-dispersed polarizing Fourier transform spectrometer

Citation

M. Buchan, D. Naylor, B. Gom, A. Christiansen, A. Anderson, A. Cournoyer, É. Carbonneau, H. Bourque, P. Ade, and C. Tucker. "Design and end-to-end validation of a cryogenic far-infrared post-dispersed polarizing Fourier transform spectrometer". Journal of Astronomical Telescopes, Instruments, and Systems, 11(3):031640, 2025. DOI: 10.1117/1.JATIS.11.3.031640.
Journal Article

Abstract

The PRobe far-Infrared Mission for Astrophysics (PRIMA) will feature a large cryogenically cooled telescope that will enable astronomical spectroscopy at both low resolution and high resolution over a broad spectral range. In the absence of telescope self-emission and with access to ultra-sensitive detectors, the point source sensitivity of a broad spectral observation is limited by photon noise. The only meaningful way to reduce photon noise is by restricting the instantaneous spectral bandwidth observed by a single detector, typically to a fraction of one percent. In the case of the Far-IR Enhanced Survey Spectrometer (FIRESS) instrument, low resolution spectroscopy is achieved by using several reflection diffraction gratings to restrict the spectral bandwidth. For high resolution spectroscopy, a Fourier transform spectrometer (FTS) is placed in front of, and in series with the grating spectrometer, which serves as a post-dispersing element to achieve the same goal. The polarization encoding properties of a Martin-Puplett interferometer can exploit the strong polarization dependence of the low resolution diffraction grating, by ensuring the interferometer output presents the transverse magnetic (TM) polarization mode to the grating. We term this hybrid instrument the post-dispersed polarizing Fourier transform spectrometer (PDPFTS). A fully cryogenic far-infrared PDPFTS has been developed in our laboratory to gain a better understanding of the challenges presented by this novel instrument. The results presented in this paper will help to guide the development of FIRESS.