Ablation and spallation of gold films irradiated by ultrashort laser pulses

Abstract

By extending molecular dynamics simulation to the experimental micrometer length scale, we observed, for the rst time, the complete dynamics of gold lms subjected to ultrashort (1 ps) laser irradiation, culminating in cavitation then ablation of the melt at the front, and crack nucleation then spallation at the rear side of the sample. For thick lms (> 0.5 µm) ablation and spallation are spatially separated; whereas for thin lms, they merge into a unique damage process, which leads to a dependence of ablation threshold on lm thickness. This work provides new insights into thermomechanical dynamics of irradiated metal lms, including coupling-decoupling of ablation and spallation processes, and opens up a eld of direct comparison between experiment and atomistic simulations.

Generation of subsurface voids and a nanocrystalline surface layer in femtosecond laser irradiation of a single-crystal Ag target

“…The atomistic molecular dynamics (MD) simulation technique has indeed been instrumental in providing valuable information on the microscopic mechanisms of laser melting [19][20][21][22], photomechanical spallation and ablation [19,[23][24][25][26][27][28][29]. Beyond the analysis of the initial dynamic material response to the fast laser energy deposition, however, there has been little progress in extending the simulations to the investigation of processes responsible for the formation of complex surface morphologies and microstructures of the laser-processed targets.…”

Atomistic simulation of laser ablation of gold: The effect of electronic pressure

“…At higher F abs the faster electron-driven tens nm deep ablation is present as well. However in this case it cannot be distin-guished from much deeper hundreds nm deep ablation due to the rarefaction wave formation (like in [12]) which starts to be realized. Therefore the dependence d(F abs ) has the second ablation threshold.…”

“…Therefore the dependence d(F abs ) has the second ablation threshold. Such a peculiarity of the dependence d(F abs ) may be the reason of the overestimation of the ablation threshold and depth in the previous models of subpicosecond pulses [4,12].…”

“…The energy transfer from the ES to the IS is implemented using a Langevin thermostat. This approach can be used to describe many features of laser ablation but it gives significant overestimation of the crater depth d as was shown for Cu [9] and Au [12]. This 2T model does not take into account the effects of electronic pressure build-up [13,14] and the changes of interionic forces as a result of the ES excitation [15,16].…”

Cold ablation driven by localized forces in alkali halides

“…At higher laser peak powers, providing F is in the range of 300-500 mJ cm À 2 , the system is often pushed into a metastable liquid phase as a result of rapid heating and melting. In such a metastable state, homogeneous bubble nucleation leads to the removal of large fragments of the material through processes known as spallation, phase explosion and fragmentation 5,6 . With even higher F (41 J cm À 2 ), the solid surface changes directly into a gaseous plasma via multiphoton ionization.…”