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The feasibility of a compact Fourier-Transform-Imaging-Spectrometer (FTIS) for small satellite remote sensing missions is currently being studied under ESA contract. Compared to classical hyperspectral imagers using dispersive spectrometers the major advantages of the FTIS is the compact optics module and the tolerable higher detector temperature, thus easing the instrument thermal design. The feasibility of this instrument concept will be demonstrated by breadboarding.

A Michelson interferometer with plane mirrors and dynamic alignment has been built for use in emission and dispersive Fourier-transform spectroscopy. The spectral range is 0.2–1.5 urn with a resolving limit of 0.03 cm-1 In spite of automatic adjustment control, some disturbances in the interferogram always remain and lead to distortions in the spectra. There are deviations from linearity in the mirror drive, linear phase errors, tilt of the moving mirror, and vibrations of the mechanical set-up. To identify and quantify these errors, the phase and amplitude of a laser interferogram are analysed by means of a special algorithm. Results are presented.

We present a Fourier Transform spectrometer where as an interferogram, fringes of equal thickness (Fizeau fringes) are recorded instead of the usual fringes of equal inclination (Haidinger rings). An image of the Fizeau fringes being formed on the diode array of a CCD camera allows us to scan the interferogram without moving a mirror or any other element. As the entire interferogram is registered at the same time, AC and even pulsed light sources can be analyzed. The disadvantage is low spectral resolution because the maximum path difference is limited by the size of the diode array.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present an UV-VIS Fourier Transform spectrometer with dynamic alignment and, in addition, automatic adjustment of the moving mirror before start and at each change of translation direction. In dynamic alignment the phase difference of laser interferograms from three points of the field of view is used to activate transducers holding the moving mirror. Whenever a run of the mirror is finished there is no interferogram for a few moments till the next run starts. The direction of translation is now opposite and due to the discontinuity of frictional forces in the drive there can be a misalignment of the moving mirror. If the misalignment leads to a phase difference greater than (pi) between the laser interferograms, correct alignment cannot be refound. To overcome this difficulty one can generate many laser interferograms instead of only three. Unless the interferograms from neighbor spots are out of phase by more than (pi) , the mirror can be realigned. Another solution of the problem which we present here is to modify the tilt of the moving mirror by means of piezo translators until the visibility of the interferogram of an expanded laser beam is at maximum.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A method is described to measure electron densities in plasmas with a sufficiently strong magnetic field superposed. The profiles of the spectral lines emitted by such a plasma are shaped by the Stark and Zeeman effect (Lorentz-triplet). Eliminating the central Zeeman component by a polarizer or observing in field direction, one gets a doublet, in which for a given spectral line and magnetic field strength the ratioI0/Iz of minimum to maximum intensities is only a function of the electron density. Measuring this ratio one finds the corresponding densities by means of calibration curves given below for the He I lineλ=5876 a. This calibration is independent of the spectral arrangement, when utilizing a polarizer for the spectral observation.