Frequency and temperature dependence of the refractive index of sapphire

摘要: Because the index of refraction is temperature dependent, a gradient across window causes image blur and bore sight error. Prior to this paper, there have been no direct temperature-dependent measurements reported on mid-infrared refractive for sapphire, popular infrared material high durability. Measurements dn/dT are ordinary ray sapphire in 4 μm region first time. Accurate frequency dependent models can now be constructed from visible index, far-infrared reflectance measurements, thermo-optic coefficient absorption coefficient. Visible determine contribution electronic transitions. Far-infrared contributions fundamental lattice vibrations (phonons). Infrared data used parameters multiphonon sum band model. By applying Hilbert transform model, model refractivity obtained. Two- three-phonon important an accurate that includes dependence. Results ordinary- extraordinary-rays