Effects of cryogenic contaminants on optical surfaces: calculations of reflectance and transmittance (CALCRT) thin-film reflectance/transmittance model

William T. Bertrand; Bob E. Wood; Kent F. Palmer

doi:10.1117/12.190134

19 October 1994 Effects of cryogenic contaminants on optical surfaces: calculations of reflectance and transmittance (CALCRT) thin-film reflectance/transmittance model

William T. Bertrand, Bob E. Wood, Kent F. Palmer

Author Affiliations +

Proceedings Volume 2261, Optical System Contamination: Effects, Measurements, and Control IV; (1994) https://doi.org/10.1117/12.190134
Event: SPIE's 1994 International Symposium on Optics, Imaging, and Instrumentation, 1994, San Diego, CA, United States

Abstract

Contamination of infrared sensor systems is an area of concern to spacecraft operators and designers. This paper describes the CALCRT mathematical model which can be used for calculating the reflectance and transmittance effects of thin contaminant films on optical surfaces. It uses an optical property data base that contains the cryogenic optical properties (refractive and absorptive indices) for satellite material outgassing products, atmospheric gases, propellants, and bipropellant plume products. The bipropellant plume data were obtained during firings of a 5 lb. thrust monomethylhydrazine/nitrogen tetroxide engine. Contaminant effects can be calculated as a function of substrate refractive index, incidence angle, film thickness, film materials, wavelength, and wavenumber. The model has been modified to treat the case when the condensate contains a mixture of molecular species or when a deposit on a surface consists of a `stack' of uniform layers, each of which has a distinct material composition. Computed transmittance spectra of selected films of mixtures are compared with transmittance spectra calculated with measured optical constants of the mixture.

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William T. Bertrand, Bob E. Wood, and Kent F. Palmer "Effects of cryogenic contaminants on optical surfaces: calculations of reflectance and transmittance (CALCRT) thin-film reflectance/transmittance model", Proc. SPIE 2261, Optical System Contamination: Effects, Measurements, and Control IV, (19 October 1994); https://doi.org/10.1117/12.190134

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