PHOTON-PHONON INTERACTION IN THIN FILMS
Scientific rept. no. 2
PARIS-6 UNIV (FRANCE) LAB DE PHYSIQUE DES SOLIDES
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The normal modes of vibrations in a perfect crystal lattice resulting into net electric dipole moment with electric vector perpendicular to the propagation vector are strongly coupled with the radiation field. The resulting optical absorption is very strong at the frequencies of the transverse optical modes. Direct absorption studies can therefore be conducted only on thin films. We examine here the particular case of thin films where the photon-phonon interaction can be treated in the frame of the collision theory for two types of particles, as a two-step process first the strong coupling of the radiation field with the phonon field in terms of polaritons and the consequent polariton decay as a second step. The optical absorption at the normal mode frequencies is calculated in terms of band width related respectively to the polariton life time, to the phonon life time and to the elastic diffusion of photons.
- Solid State Physics