Melting threshold and melt removal dynamics during laser interaction with steel and HgCdTe in femtosecond regime

The results of a study of a single 200 femtosecond laser pulse interaction with thick stainless steel and HgCdTe samples are reported. The threshold pulse energies required to produce sample surface melting are measured. The melt dynamics, material removal rate and evolution of surface morphology were observed for different pulse energies and number of laser pulses. It was observed that, similarly to long laser pulse interaction, a layer of melt can be produced at the sample surface. Increase of laser pulse energy results in melt ejection in the radial direction toward the periphery of the interaction zone resembling evaporation recoil melt removal typical for laser interaction in range from nanosecond to cw. The removal of material from stainless steel sample was observed to be highly nonuniform. The columnar structures were observed on the surface of stainless steel samples. The period of these structures is dependent on laser pulse energy and number of pulses. The observed melting threshold is compared with the theoretical prediction obtained using two-temperature model.