On a new method of acoustic monitoring of the nanosecond laser ablation of metals

The possibility of acoustic detection of submicron displacement of a metal surface during ablation induced by a nanosecond ($\sim 550$ ns) train of $\sim 70$ short ($\sim 60$ ps) laser pulses has been demonstrated experimentally for the first time. The detection is based on the comparison of time structures of modulation of the laser intensity and recoil pressure in an irradiated target observed by a piezoelectric sensor. The displacement at low intensities of irradiation is due to thermal expansion. With an increase in the intensity, the displacement changes sign because of the development of ablation processes in the irradiated region. The proposed method makes it possible to obtain new information on the behavior of a material, in particular, under the conditions of extreme phase nonequilibrium under intense laser irradiation.