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The refractive optical design of the James Webb Space Telescope (JWST) NearInfrared Camera (NIRCam) uses three infrared materials in its lenses: LiF,BaF2, and ZnSe. In order to provide the instrument's optical designers withaccurate, heretofore unavailable data for absolute refractive index based onactual cryogenic measurements, two prismatic samples of each material weremeasured using the cryogenic, high accuracy, refraction measuring system(CHARMS) at NASA's Goddard Space Flight Center (GSFC), densely covering thetemperature range from 15 to 320 K and wavelength range from 0.4 to 5.6microns. Data reduction methods are discussed and graphical and tabulated datafor absolute refractive index, dispersion, and thermo-optic coefficient forthese three materials are presented for selected wavelengths and temperaturesalong with estimates of index uncertainty. Coefficients fortemperature-dependent Sellmeier fits of measured index are also presented withan example of their usage to predict absolute index at any wavelength ortemperature within the applicable range of those parameters.

High accuracy, absolute, cryogenic refractive index measurements of infrared lens materials for JWST NIRCam using CHARMS