On the theory of relaxation of electrons excited by femtosecond laser pulses in thin metallic films

We develop a theory of electron-phonon interactions in thin metallic films in order to explain the behavior of the carrier relaxation rate with film t hickness. In the theoretical approach presented here we take into account t he quantization of the phonon spectrum which is a result of phonon confinem ent. The main consequences of the quantization of the phonon spectrum are: (1) the existence of a nonzero lower limit of acoustic phonon frequency and wave vector, and (2) kinematic restrictions following from the energy and momentum conservation laws. We conclude that these consequences reduce the available region of phase space of electron-phonon scattering probability.