Drilling of steel and HgCdTe with the femtosecond pulses produced by a commercial laser system

The results of interaction of single and multiple 200 fs laser pulses with thick stainless steel and HgCdTe samples are reported. The threshold laser energy density required to produce surface melting is measured. The melt dynamics and evolution of surface morphology are observed for different pulse energies and number of laser pulses. It is observed that, as with a long laser pulse interaction, a layer of melt can be produced at the sample surface. Melt ejection in the radial direction towards the periphery of the interaction zone is observed when the pulse energy is increased. The observed melt dynamics resembles the evaporation recoil melt removal typical of the laser interactions in the range from nanoseconds to continuous wave (CW). The observed melt ejection is attributed to a nanosecond component of the laser pulse with an estimated energy of approximately 25% of the total laser pulse energy. The measured melting threshold energy density for stainless steel is comparable with the published theoretically predicted threshold for nickel computed using a two-temperature model.