Thermal regime of laser ablation of metals by ultrashort pulses of low fluence

Thermal ablation of a metal surface by low-energy ultrashort laser pulses is considered theoretically. The temporal dynamics of the surface electron and lattice temperatures is studied within the framework of the two-temperature model and for different temperature dependences of the characteristics of the metal (electron-relaxation time, heat capacity, thermal conductivity). The approximation of evaporation into a vacuum is used to determine the ablation depth. Analytical expressions for the ablation-threshold fluenceFth as well as the threshold values of the lattice temperatureTth (Fth) and the characteristics time of lattice temperature decaytd (Fth) are obtained. This analytical description is in satisfatory agreement with particular numerical calculations.