Trapped phonons in ultrathin metal films: the interpretation of recent femtosecond experiments

The results of recent experimental and theoretical studies of the nonequilibrium dynamics of electrons and phonons excited by femtosecond laser pulses in ultrathin metal films are discussed. Experimental data obtained by the femtosecond pump – probe wave (FPPW) method are analysed using a two-temperature model and non-thermal models. A key role of the size quantisation of a phonon spectrum in the dynamics of phonons and electron – phonon interaction is substantiated. The application of the FPPW method in superconductivity studies is also discussed.