22 December 2003 Helium cryo testing of an SLMS (silicon lightweight mirrors) athermal optical assembly
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Abstract
SLMS athermal technology has been demonstrated in the small 4-foot helium cryogenic test chamber located at the NASA/MSFC X-Ray Calibration Facility (XRCF). A SLMS Ultraviolet Demonstrator Mirror (UVDM) produced by Schafer under a NASA/MSFC Phase I SBIR was helium cryo tested both free standing and bonded to a Schafer designed prototype carbon fiber reinforced silicon carbide (Cesic) mount. Surface figure data was obtained with a test measurement system that featured an Instantaneous Phase Interferometer (IPI) by ADE Phase Shift. The test measurement system's minimum resolvable differential figure deformation and possible contributions from test chamber ambient to cryo window deformation are under investigation. The free standing results showed differential figure deformation of 10.4 nm rms from 295K to 27K and 3.9 nm rms after one cryo cycle. The surface figure of the UVDM degraded by lambda/70 rms HeNe once it was bonded to the prototype Cesic mount. The change was due to a small astigmatic aberration in the prototype Cesic mount due to lack of finish machining and not the bonding technique. This effect was seen in SLMS optical assembly results, which showed differential figure deformation of 46.5 nm rms from 294K to 27K, 42.9 nm rms from 294K to 77K, 28.0 nm rms from 294K to 193K and 6.2 nm rms after one cryo cycle.
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Marc T. Jacoby, William A. Goodman, H. Philip Stahl, Andrew S. Keys, Jack C. Reily, Ron Eng, James B. Hadaway, William D. Hogue, Jeffrey R. Kegley, Richard D. Siler, Harlan J. Haight, John Tucker, Ernest R. Wright, James R. Carpenter, Jeff E. McCracken, "Helium cryo testing of an SLMS (silicon lightweight mirrors) athermal optical assembly", Proc. SPIE 5180, Optical Manufacturing and Testing V, (22 December 2003); doi: 10.1117/12.508378; https://doi.org/10.1117/12.508378
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