All-reflection Michelson interferometer: analysis and test for far ir Fourier spectroscopy

The beam splitter of the all-reflection Michelson interferometer consists of a combination of three parallel diffraction gratings. This paper extends the analysis of the instrument to include the effects of lateral errors in the grating adjustment (i.e., displacements parallel to the grating faces and perpendicular to the grooves). Such errors are shown to introduce a phase shift independent of wavenumber and proportional to grating order number. Tests of an instrument designed for Fourier transform spectroscopy in the 500-1000-micron spectral range are reported and shown to be in agreement with the analysis. For wavenumbers which pass through the instrument in 2 or more orders, cross-order interference effects are expected to occur which cause rapid variations in the efficiency vs. wavenumber curve. This possibility should be eliminated in the design of a practical instrument. The resolution of the test instrument (1.6/cm) was insufficient to reveal this effect.