CTE effects of CVD silicon carbide cladding of a silicon carbide optic

David Crompton; Wayne Hambek; Keri Goris; David Klick; Gary Swanson; Hugo Vargas; Mark Wilder

doi:10.1117/12.2626710

3 October 2022 CTE effects of CVD silicon carbide cladding of a silicon carbide optic

David Crompton, Wayne Hambek, Keri Goris, David Klick, Gary Swanson, Hugo Vargas, Mark Wilder

Proceedings Volume 12221, Optical Manufacturing and Testing XIV; 1222113 (2022) https://doi.org/10.1117/12.2626710
Event: SPIE Optical Engineering + Applications, 2022, San Diego, California, United States

Conference Poster

Abstract

Silicon carbide’s material properties make it a desirable choice as a mirror substrate, particularly for space-based optical systems where thermal stability and low mass are critical. Mirror substrates made from silicon carbide (SiC) often have a small amount of porosity or surface features that make optical surfacing of the bare substrate challenging. To achieve the surface figure and roughness required for diffraction-limited performance at visible wavelengths, it is common to apply a thin layer, or cladding, of a similar material that has properties more conducive to optical surfacing. The introduction of another material, however, has the potential to change the surface figure over temperature, even with small differences in thermal expansion between the cladding and the substrate. This paper presents testing to characterize that effect on a SuperSiC®-SP mirror clad with chemical vapor deposited (CVD) silicon carbide produced by Entegris Specialty Materials. This mirror was fabricated for a two-axis gimbal-mounted scan mirror assembly, which has been developed for the QZSS-HP program. The QZSS-HP is a hosted payload (HP) on the Japanese Quasi-Zenith Satellite System (QZSS) and will be used for space domain awareness (SDA). Thermal expansion measurements and optical surface measurements performed at Massachusetts Institute of Technology Lincoln Laboratory (MIT LL) show that the difference in coefficient of thermal expansion (CTE) is on the order of 0.2 parts per million per degree C.

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David Crompton, Wayne Hambek, Keri Goris, David Klick, Gary Swanson, Hugo Vargas, and Mark Wilder "CTE effects of CVD silicon carbide cladding of a silicon carbide optic", Proc. SPIE 12221, Optical Manufacturing and Testing XIV, 1222113 (3 October 2022); https://doi.org/10.1117/12.2626710

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