Temperature Dependence of Multiphonon Absorption in Fluorite Crystals
We report measurements of the absorption coefficients of CaF2, SrF2 and BaF2 in the frequency range ∼700 to ~1600 cm−1, at temperatures ranging from 300 to 800°K. The frequency dependence is found to be nearly exponential-like in the temperature range investigated, in agreement with existing multiphonon theories. A detailed analysis of the measured temperature dependence, utilizing the theories of Bendow, and of Namjoshi and Mitra, shows that the observed behavior conforms overall to that predicted for intrinsic multiphonon processes. The role of the temperature dependence of the phonon spectrum in suppressing the temperature dependence of the multiphonon absorption is also investigated.
KeywordsPhonon Frequency Longitudinal Optical Optical Phonon Frequency Room Temperature Absorption Fluorite Crystal
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