Dynamics of Interacting Photon-Phonon Fields in Dielectric Crystals

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Abstract
The dynamic interaction between electromagnetic waves and transverse optical phonons in dielectric crystals has been studied by means of the Green's-function method. Emphasis has been given to the line shapes of the absorption bands at finite temperatures. The spectral functions for the photon and phonon fields are found to consist of the superposition of symmetric and asymmetric Lorentzian lines even if the frequency dependence of the energy shift and damping functions is neglected. The source of the asymmetry is the anharmonic coupling between the transverse photons and transverse optical phonons. General expressions for the energy shift and the damping functions are derived. The possible mechanisms that may occur in the physical process of Raman scattering are examined in detail, and expressions for the corresponding scattering amplitudes are developed. In the limiting case of absence of dispersion of the electromagnetic waves in the medium, the bare excitation spectra for both fields are also discussed.