Pulse-by-pulse depth profile measurement of femtosecond laser ablation on copper

Pulse-by-pulse depth profile measurements were performed during femtosecond laser pulse irradiation on copper. The evolution of the ablation depth and the surface roughness during multi-pulse irradiation was investigated using a three-dimensional microscope. We found that a number of pulse irradiation was required to activate constant-rate ablation and the number of pulses depended on the fluence. We conclude that laser-induced embrittlement of a target material plays a decisive role to determine the ablation rate during multiple-pulse irradiation.