COHERENT RELAXATION OF HIGH-FREQUENCY PHONON-POLARITONS

Phonon-polaritons are an extremely important manifestation of the interaction between the electromagnetic field and mechanical vibration in polar crystals. This interaction leads to the formation of a localised quasi-particle which may transport energy over large distances inside the solid. Because of their significant frequency-dispersion, phonon-polariton wave-packets couple to many other states of the crystal introducing new relaxation pathways. These properties also mean that polaritons can be employed as a probe of crystal inhomogeneity, including internal disorder and surfaces.