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Proceedings Paper

Cryogenic Testing Of Mirrors For Infrared Space Telescopes
Author(s): Jacob H. Miller; Fred C. Witteborn; Harold J. Garland
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Paper Abstract

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).

Paper Details

Date Published: 4 November 1982
PDF: 6 pages
Proc. SPIE 0332, Advanced Technology Optical Telescopes I, (4 November 1982); doi: 10.1117/12.933548
Show Author Affiliations
Jacob H. Miller, NASA/Ames Research Center (United States)
Fred C. Witteborn, NASA/Ames Research Center (United States)
Harold J. Garland, INSPEC Applied Optics and Electronics (United States)

Published in SPIE Proceedings Vol. 0332:
Advanced Technology Optical Telescopes I
Lawrence D. Barr; Geoffrey Burbidge, Editor(s)

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