INVESTIGATION OF ELECTRONIC FRINGE DETECTOR FOR STELLAR INTERFEROMETER
TECHNICAL OPERATIONS INC BURLINGTON MA
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A fringe detector was constructed to detect fringes from a Michelson stellar interferometer and to relate these measurements to the characteristics of the source of illumination. This instrument has variable separation apertures adjustable from 0.6 to 6 cm. Aperture height is maintained at 0.1 times the separation. An optical system produces the fringe pattern by superimposing the partially coherent light entering the two apertures. A rotating reflector, single slit, and phototude combine to transform the spatially varying intensity pattern of the fringe field into a time-varying voltage signal displayed on an oscilloscope face. The oscilloscope trace is photographed and analyzed to determine fringe contrast. The maximum sensitivity of the detector was determined to be equivalent to a source providing 10 to the minus 10th power wattssq cm at a fringe contrast of 1 and a signal-to-noise ratio of 1. Improvements in the entrance aperture configuration, phototube sensitivity, and the use of a grating instead of a single slit can provide a factor of 500 to 1000 improvement in detector sensitivity. The interferometer was determined to have potentially better resolution than a single-mirror telescope because it can electrically filter the effects of ambient background illumination and turbulence. The use of an interferometer to measure the angular size of a pie-shaped source was studied and found to be not particularly suited to this purpose.