Frequency and temperature dependence of the refractive index of sapphire

被引:63
作者
Thomas, ME
Andersson, SK
Sova, RM
Joseph, RI
机构
[1] Johns Hopkins Univ, Appl Phys Lab, Laurel, MD 20723 USA
[2] Univ Uppsala, Dept Technol, S-75121 Uppsala, Sweden
关键词
refractive index; sapphire; phonon;
D O I
10.1016/S1350-4495(98)00010-3
中图分类号
TH7 [仪器、仪表];
学科分类号
0804 ; 080401 ; 081102 ;
摘要
Because the index of refraction is temperature dependent, a temperature gradient across a window causes image blur and bore sight error. Prior to this paper, there have been no direct temperature-dependent measurements reported on the mid-infrared refractive index for sapphire, a popular infrared window material of high durability. Measurements of dn/dT are reported on the ordinary ray of sapphire in the 4 mu m region for the first time. Accurate temperature and frequency dependent refractive index models can now be constructed from visible measurements of the refractive index, far-infrared reflectance measurements, thermo-optic coefficient 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- and extraordinary-rays are obtained. (C) 1998 Elsevier Science B.V. All rights reserved.
引用
收藏
页码:235 / 249
页数:15
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