The history of the subject was traced from the discovery of color centers in alkali halides to current research on the coherent generation and dephasing of vibrations in solids. A series of ever more sophisticated experimental methods had made it possible to understand the temporal, spectral and spatial response of insulators, semiconductors, superconductors and metals to various forms of excitation. Among the observed phenomena were the crystal field splitting of atomic states in ionic materials, localized and extended phonon states in alkaline earth halides, spatial and temporally resolved phonon transport in various materials, the generation of coherent phonon and polariton states in semiconductors, the dephasing of coherent states and observations of a long sought-after long-lived phonon state.

W.E.Bron: Journal of the Physics and Chemistry of Solids, 1994, 55[12], 1381-91