23 June 1994 Silicon carbide mirror cryogenic distortion testing
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A silicon carbide mirror has been holographically tested at cryogenic temperatures in an attempt to determine the level of surface distortion as a function of temperature. The test was conducted using the 1M thermal vacuum holographic test chamber, located at the Hughes El Segundo facility. The mirror was initially tested in February 1993, using full thermal strapping of the mirror blank, this allowed the mirror to reach a temperature of 48 Kelvin (K). Digitization of the holograms showed a distinct parallel pattern on the surface which corresponded to the webs located on the back of the mirror. A second test was conducted in June 1993, using only the thermal shrouds to cool the mirror. Without the thermal straps attached the mirror exhibited significantly different performance. With thermal strapping the mirror figure distortion was 2.15 waves peak-to-valley (P-V), 0.5 waves rms at a temperature of 184 K, when the test was repeated without straps the mirror figure distortion averaged 0.69 waves P-V, 0.15 waves rms at a temperature of 181 K and a measurement wavelength of 0.514 micrometers.
© (1994) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
David G. Michel, David G. Michel, } "Silicon carbide mirror cryogenic distortion testing", Proc. SPIE 2227, Cryogenic Optical Systems and Instruments VI, (23 June 1994); doi: 10.1117/12.178601; https://doi.org/10.1117/12.178601

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