Mechanical disturbances in Fourier spectrometers

Fourier spectrometers are sensitive to many kinds of disturbance. This focus is mainly on those connected to mechanical vibrations, assessing the relationships between the mechanical inputs and the deriving effects on the spectra. Mechanical vibrations have two main effects on the spectra, the addition of signals due to direct sensitivity to vibrations of the detectors (e.g., through piezoelectric effect) and the changes of the interferogram due to the interferometer optical components motion. The Fourier transform spectrometer considered in this study is based on the constant optical path step sampling achieved by using the interferogram of a reference laser as a trigger so, ideally insensitive to mirrors speed changes, however, the analysis will show how the effects of delays in the sampling chain can compromise the benefits of this configuration. The effects of the vibration of the interferometer optical alignment are considered as well, showing the effect produced on the interferograms and eventually on the spectra. Despite their nonmechanical nature, detector nonlinearity and internal optical reflections are considered as well because their effects, similar to the mechanical ones, could be confused with the latter while in spectra diagnostic it is often important to be able to distinguish between the two. For all the analyzed effects the quantitative relationships between the mechanical disturbances' amplitudes and spectral observed effects are derived.