LOW-FREQUENCY PHONON STRUCTURES IN DISORDERED-SYSTEMS PROBED BY FEMTOSECOND NONLINEAR SPECTROSCOPY

The femtosecond optically heterodyne-detected optical Kerr effect and polarization-selective impulsive stimulated light scattering technique s have been applied to probe low-frequency phonon structures in disord ered systems such as liquids, polymers and glasses. This information i s particularly important to understand the various relaxational phenom ena in the optical response of molecules in disordered systems.