Relaxation and Propagation of High Frequency Phonons in Thin Crystalline Plates After Intense Laser Pumping

Abstract

One of the most interesting and important problems in phonon physics is that of the relaxation of nonequilibrium phonons in the course of the establishment of an equilibrium temperature formation in the crystal. The initial stage of such relaxation in the case of weak excitation of the phonon system, when spontaneous phonon decay dominates, was investigated, in particular, in Refs. 1–2. To describe the whole course of phonon relaxation, including the temperature formation stage, one must take into account the phonon-phonon coalescence processes along with the decay processes(3). At sufficiently high excitation levels, when the temperature increase ΔT = Tf - TO≃ TO, phonon coalescence can be significant from the very beginning or the relaxation process. The latter situation is rather common for intense laser excitation, and can also occur in the case of current pulse excitation of phonons.