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Two recently developed optical coatings, ion-beam-deposited silicon carbide and ion-beam-deposited boron carbide, are very attractive as coatings on optical components for instruments for space astronomy and earth sciences operating in the extreme-UV spectral region because of their high reflectivity, significantly higher than any conventional coating below 105 nm. To take full advantage of these coatings in space applications, it is important to establish their ability to withstand exposure to the residual atomic oxygen and other environmental effects at low-earth-orbit altitudes. The first two flights of the Surface Effects Sample Monitor experiments flown on the ORFEUS-SPAS and the CRISTA-SPAS Shuttle missions provided the opportunity to study the effects of space exposure on these materials. The results indicate a need to protect ion-beam-deposited silicon-carbide-coated optical components from environmental effects in a low-earth orbit. The boron-carbide thin-film coating is a more robust coating able to withstand short-term exposure to atomic oxygen in a low-earth-orbit environment.

We flew specimens of eight different optical coating materials in low earth orbit as part of the Long Duration Exposure Facility manifest to determine their ability to withstand exposure to the residual atomic O and other environmental effects at those altitudes. We included samples of Al, Au, Ir, Os, Pt, Al + MgF2, Al + SiOx, and chemical-vapor-deposited SiC, representing reflective optical applications from the vacuum ultraviolet through the visible portions of the spectrum. We found that the majority of the materials suffered sufficient reflectance degradation to warrant careful consideration in the design of future space-flight instrumentation

The normal-incidence reflectance of high-density cast silicon carbide (SIC) is evaluated in the extreme ultraviolet (EUV) spectral region. High reflectivity in the EUV is achieved. High reflectivity and the relatively low-cost manufacturing process make high-density cast SiC a promising mirror material for EUV applications. Key words: Silicon carbide, extreme ultraviolet, optical materials, reflectivity.

Evaluates the normal-incidence reflectance of high-density cast silicon carbide (SiC), in the extreme ultraviolet (EUV) spectral region. Spectral region range in which high-density cast SiG was evaluated; How the reflectance measurements were made; Characteristics which make high-density SiC promising mirror material for EUV applications.