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4 November 1982 Cryogenic Testing Of Mirrors For Infrared Space Telescopes
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An optical test facility has been built for testing candidate mirror materials for the Shuttle Infrared Telescope Facility (SIRTF). Mirrors as large as 66 cm in diameter can be tested at temperatures down to about 10K for changes in optical figure of a fraction of a wave from their room temperature figure. Tests of two fused silica mirrors, 50 cm in diameter, are underway. The test mirror is heat sunk to the helium reservoir with copper straps whose connection to the mirror is accomplished by soldering individual strands of copper to small silver spots diffused into the unfigured side of the mirror. This permits relatively fast, conductive cooling of the mirror. In the first test, cooling from 300 to 80K took 4 days; cooling from 80 to 12.5K took 24 hours. Optical access to the cold mirror is through a small (5 cm diameter) glass port in the vacuum chamber placed a few cm short of the radius of curvature of the mirror. A Shack interferometer is used to examine the mirror figure throughout the cool-down. Interferograms are photographed and the fringe patterns are digitized. Contour plots of mirror figure are then calculated using the University of Arizona's FRINGE program on our CDC 7600 computer. Preliminary analysis of interferograms of one of the mirrors shows very little change in figure between 293K and 10.5K (change in rms OPD=0.027 waves).
© (1982) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Jacob H. Miller, Fred C. Witteborn, and Harold J. Garland "Cryogenic Testing Of Mirrors For Infrared Space Telescopes", Proc. SPIE 0332, Advanced Technology Optical Telescopes I, (4 November 1982);

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