26 July 1999 Emissivity of a uniaxial crystalline slab
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Abstract
Sapphire is a commonly used dome material. It is uniaxial and features different propagation properties depending on propagation direction and crystallographic orientation to the window boundary. These differences are particularly important for a hemispherical dome geometry. Prior work examined a semi-infinite medium. However, to be practical, a medium of finite thickness must be considered. The purpose of this paper is to present the results of a detailed calculation of the direcitonal emissivity of a finite sheet of uniaxial crystal located in an isotropic environment when the parallel plane surface so the crystal sample have an arbitrary orientation with respect to the crystallographic axes. Furthermore, the permittivities of the uniaxial crystal are allowed to have a complex part. Transmission measurements between 1400 cm-1 and 2500 cm-1 using a Fourier transform spectrometer are used in conjunction with the present theoretical result to determine the room temperature multiphonon absorption coefficient for the extraordinary-ray of sapphire. Application of the theory to a dome geometry is described.
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Richard I. Joseph, Patrick S. Wayland, Michael E. Thomas, "Emissivity of a uniaxial crystalline slab", Proc. SPIE 3705, Window and Dome Technologies and Materials VI, (26 July 1999); doi: 10.1117/12.354637; https://doi.org/10.1117/12.354637
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