Non-thermal lattice dynamics in α-quartz induced by femtosecond laser pulses: An ab initio study

Laser-patterning techniques are typically based on local-heating phenomena, whereas recently developed short-pulse lasers operating on the order of femtoseconds may also induce non-thermal processes in materials. As it is difficult to study non-thermal processes experimentally, ab initio simulations are crucial for understanding laser-patterning phenomena under these conditions. In this study, real-time time-dependent density functional simulations were performed to examine the kinetic energies of the atoms in a slab of α-quartz under a laser fluence per pulse of 10 J/cm2, a wavelength of 800 nm, and full width at half-maximum (FWHM) values ranging from 10 fs to 100 fs. The simulation results suggested the occurrence of thermal/non-thermal crossover at an FWHM value of approximately 50 fs. Smaller FWHM values resulted in non-thermal lattice dynamics. Even under a lower laser fluence per pulse, a shorter pulse initiated non-thermal dynamics with a duration of several tens of femtoseconds.