Dynamics of spallation during femtosecond laser ablation studied by time-resolved reflectivity with double pump pulses

作者：Kumada Takayuki^*; Otobe Tomohito; Nishikino Masaharu; Hasegawa Noboru; Hayashi Terutake

来源：Applied Physics Letters, 2016, 108(1): 011102.

DOI：10.1063/1.4939231

The dynamics of photomechanical spallation during femtosecond laser ablation of fused silica was studied by time-resolved reflectivity with double pump pulses. Oscillation of reflectivity was caused by interference between the probe pulses reflected at the sample surface and the spallation layer, and was enhanced when the surface was irradiated with the second pump pulse within a time interval, Delta tau, of several picoseconds after the first pump pulse. However, as Delta tau was increased, the oscillation amplitude decreased with an exponential decay time of 10 ps. The oscillation disappeared when Delta tau exceeded 20 ps. This result suggests that the formation time of the spallation layer is approximately 10 ps. A second pump pulse with Delta tau shorter than 10 ps excites the bulk sample. The spallation layer that is photo-excited by the first and second pump pulses is separated afterward. In contrast, a pulse with Delta tau longer than the formation time excites and breaks up the spallation layer that has already been separated from the bulk. The formation time of the spallation layer, as determined in this experiment, is attributed to the characteristic time of the mechanical equilibration corresponding to the thickness divided by the sound velocity of the photo-excited layer.

• 出版日期2016-1-4