The microscopic nonequilibrium process in solids under transient heating

A brief review of studies on the dynamic process of thermal expansion since the eighties is given. A magnitude of difference of one to two orders between the results of theoretical calculations and experimental observations of the characteristic time is discussed. The nonequilibrium localized phonon gas in a "hot spot" is studied using the Boltzmann equation, leading to a soliton-like solution. It gives the way to fill the gap of the above-mentioned difference between theory and experiment. The lattice relaxation of a laser rod is developed theoretically and verified experimentally. Different expansion processes of a high-T_c super-conductor below and above T_c imply the existence of some new features of excitons in the high-T_c state.