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

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 dependencies 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 fluence Fth as well as the threshold values of the lattice temperature Tth(Fth) and the characteristic time of lattice temperature decay td(Fth) are obtained. This analytical description is in satisfactory agreement with particular numerical calculations.