On the wave treatment of the conduction of heat in photothermal experimentswith solids

Abstract

In this paper we discuss the conduction of heat in solids excited by a periodicallytime-dependent source, commonly encountered in photothermal experiments. Inthe analysis, we take into account the relaxation time necessary for the onset ofthe heat flux which leads to a second time derivative in the heat diffusionequation. It is shown that there exists a critical modulation frequency at whichthe heat flux changes its diffusive character to a wave propagation processwith the velocity of sound. Evidence is provided for the possibility ofdetecting second sound in solids by means of a photothermal experiment.