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Proceedings Paper

Temperature dependence of the infrared refractive index of sapphire
Author(s): Michael E. Thomas; Raymond M. Sova; Richard I. Joseph
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Paper 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.

Paper Details

Date Published: 28 September 1994
PDF: 9 pages
Proc. SPIE 2286, Window and Dome Technologies and Materials IV, (28 September 1994); doi: 10.1117/12.187374
Show Author Affiliations
Michael E. Thomas, Johns Hopkins Univ. (United States)
Raymond M. Sova, Johns Hopkins Univ. (United States)
Richard I. Joseph, Johns Hopkins Univ. (United States)


Published in SPIE Proceedings Vol. 2286:
Window and Dome Technologies and Materials IV
Paul Klocek, Editor(s)

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