8 December 1998 Low-temperature figure stability of a COI all-composite mirror M4
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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.
© (1998) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
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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