Temperature dependence of the infrared refractive index of sapphire

Michael E. Thomas; Raymond M. Sova; Richard I. Joseph

doi:10.1117/12.187374

28 September 1994 Temperature dependence of the infrared refractive index of sapphire

Michael E. Thomas, Raymond M. Sova, Richard I. Joseph

Proceedings Volume 2286, Window and Dome Technologies and Materials IV; (1994) https://doi.org/10.1117/12.187374
Event: SPIE's 1994 International Symposium on Optics, Imaging, and Instrumentation, 1994, San Diego, CA, United States

Abstract

Infrared domes on guided missiles are aerodynamically heated nonuniformly. Because the index of refraction is temperature dependent, the temperature gradient can cause image blur and bore-sight error. The temperature dependence of the infrared refractive index has not been directly measured in sapphire, a popular dome material. However, an accurate model of the temperature-dependent infrared refractive index can be obtained from visible measurements of the refractive index, far-infrared reflectance measurements, and infrared measurements of the absorption coefficient. Visible measurements determine the contribution to the refractive index from electronic transitions. Far-infrared measurements determine the contributions from fundamental lattice vibrations (phonons). Infrared absorption data are used to determine parameters in a multiphonon sum band model. By applying the Hilbert transform to this multiphonon absorption model, a model for the multiphonon refractivity is obtained. Two- and three-phonon contributions to the refractive index are important for an accurate model that includes temperature dependence. Results for the ordinary ray and extraordinary ray are obtained.

Citation Download Citation

Michael E. Thomas, Raymond M. Sova, and Richard I. Joseph "Temperature dependence of the infrared refractive index of sapphire", Proc. SPIE 2286, Window and Dome Technologies and Materials IV, (28 September 1994); https://doi.org/10.1117/12.187374

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