Spatial heterodyne spectroscopy: Interferometric performance at any wavelength without scanning.

摘要

In Spatial Heterodyne Spectroscopy (SHS), the wavenumber dependent Fizeau fringe pattern produced by a dispersive two-beam interferometer provides the Fourier transform of a selected spectral interval centered on the wavenumber for which the exiting wavefronts are perpendicular to the optical axis. This displacement of the zero spatial frequency to correspond to a favorable optical wavelength is analogous to the familiar time or frequency heterodyne technique. When the Fizeau fringe pattern is recorded on a position sensitive detector of suitable sensitivity, the spectrum may be recovered from a spatial Fourier transform of the recorded image. A conventional Michelson Interferometer with its return mirrors replaced with diffraction gratings is an example of a two-beam dispersive interferometer. Since a diffraction grating may be used as a beam splitter, the concept is not restricted to spectral regions where suitable transmitting materials are available.; In a series of experimental and analytical studies, it has been shown that spectrometers operating on the SHS principal achieve the theoretical resolution limit of the gratings without scanning, but retain the large angular input tolerance of conventional scanning Fourier transform spectrometers. Field widening without moving elements can be achieved for transmitting and all-reflecting SHS configurations. The expected performance of specific SHS systems has been compared with conventional techniques for measurements of geocoronal Balmer-alpha radiation from the ground and far-ultraviolet emission lines in the interstellar medium from space.