Fabry-Perot Etalons as Prefilters for Astronomical Far Infrared Fourier Transform Spectroscopy

摘要

It is shown that a Fourier Transform Spectrometer (FTS) can be made competitive in sensitivity with Narrow Band Spectrometers (NBS) such as scanning Fabry-Perot spectrometers or grating instruments for work on specific lines in far infrared astronomy by prefiltering the radiation so that the broadband background on the detector(s) of the FTS is reduced. Fabry-Perot etalons made with electroformed metal mesh reflectors are suitable prefilters. A Fabry-Perot prefiltered FTS has a capability for simultaneous observation of lines at substantially different wavelengths in the same beam on the sky. The lines are passed by different orders of the Fabry-Perot, and their separation and resolution is accomplished by the FTS. Sensitivity of a prefiltered FTS and an NBS are compared; suitable pairs of astrophysically interesting lines are identified; technical aspects of building very compact etalons designed for use at LHe temperatures are discussed; measurements of properties of commercially available metal mesh are reported; and performances of etalons built for line pairs near 50 micrometers are indicated.