Diamond, beryllia, and cubic zirconia are potential optical window materials that feature high strength, hardness, and high melting temperatures. Diamond, in particular, is receiving considerable attention concerning the fabrication of polycrystalline films and windows. To fully appreciate the potential of these materials as infrared windows, the optical properties must be accurately known. Optical phonons, both single and multiple, determine the intrinsic absorption properties and infrared-active single-phonon transitions contribute to the index of refraction. Both beryllia and cubic zirconia are composed of ionic bonds. This means that dipole moments will exist for some of the vibrational modes and they will be infrared active. These modes can be observed in reflection spectra. The higher harmonics and combination bands of the one-phonon band form the multiphonon band absorption. The region of the three-phonon band determines the beginning of infrared transparency in these materials. Intrinsic diamond is composed of covalent bonds with a high degree of symmetry and hence has no infrared active one phonon bands. However, lattice defects produce weak one-phonon absorption bands in the region of 1000 cm. Also, multiphonon combination bands of inactive one-phonon and Raman bands produce significant absorption beyond 1800 cm. Experimental reflection spectra of beryllia and cubic zirconia from 200 to 1200 cm, and experimental transmission spectra of intrinsic type ila diamond from 500 to 5000 cm are presented. These experimental data are used to determine the necessary optical parameters for models of the complex index of refraction as a function of frequency and temperature.

Date Published: 1 October 1990
PDF: 7 pages
Proc. SPIE 1326, Window and Dome Technologies and Materials II, (1 October 1990); doi: 10.1117/12.22490

Published in SPIE Proceedings Vol. 1326:
Window and Dome Technologies and Materials II
Paul Klocek, Editor(s)