Abstract

The ω–k dispersion law of phonon polaritons is extremely sensitive to the state of the crystal medium: to small variations in composition and crystal lattice symmetry, to low-dimensional effects. Nevertheless, the scope of polariton scattering spectroscopy is not wide. Usually, the polariton scattering spectra are registered via near-forward three-wave Raman scattering |1|. As a rule, the frequency shift between a polariton and a phonon is large in comparison with the phonon dumping constant; hence, the contribution of Raman scattering tensor is negligible. The investigated medium must have second-order optical susceptibility to provide the polariton scattering. The process is reduced to the three-wave spontaneous parametric light scattering (SPS) |2|. As the polariton frequency depends strongly on the wave vector, it is necessary to analyze the frequency-angular distribution of the scattered light with high angular resolution instead of integrating over the angle, as in phonon spectroscopy. Thus, the intensity of signals under registration is usually small and insufficient to study objects with linear dimensions below 100mkm.

© 1996 IEEE