8 December 1998 Low-temperature figure stability of a COI all-composite mirror M4
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Abstract
Recent developments in the design and fabrication of very light-weight all-composite mirrors have made possible extremely well balanced, thermally stable, structures which distort very little when cooled. One such mirror is the Composite Optics, Incorporated all-composite mirror, M4, which has a 45.7 cm diameter and 3 cm thickness and a spherical surface of radius-of-curvature 2.92 meters. Relative figure measurements of this mirror were made with the Steward Observatory Light Weight Mirror Low Temperature Test Chamber over a temperature range from 20 C to -60 C using a 10.6 μm interferometer. The measurements show a remarkably small increase in the rms figure departure from a spherical surface of fixed radius-of-curvature of 0.27 μm over the 80 C temperature change. The effective coefficient of thermal expansion over this temperature range derived from the focus change is 0.66 x 10-6/C, close to that of fused silica.
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Patrick M. Woida, Patrick M. Woida, William F. Hoffmann, William F. Hoffmann, Steven J. Connell, Steven J. Connell, Eldon P. Kasl, Eldon P. Kasl, } "Low-temperature figure stability of a COI all-composite mirror M4", Proc. SPIE 3430, Novel Optical Systems and Large-Aperture Imaging, (8 December 1998); doi: 10.1117/12.332490; https://doi.org/10.1117/12.332490
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