Dynamic Structure and Mass Penetration of Shock Wave in Picosecond Laser-Material Interaction

Abstract

This work pioneers the atomistic modeling of the shock wave in background gas in picosecond laser-material interaction. It is found in the shock wave the compressed ambient gas region has a very uniform temperature distribution while the temperature decreases from the front of the plume to its end. The group velocity of atoms in the shock wave front is much smaller than the shock wave propagation speed and experiences a fast decay due to momentum exchange with the ambient gas. Strong decay of the shock wave front temperature and pressure is observed while its density features much slower attenuation. An effective mass penetration length is designed to quantitatively evaluate the mutual mass penetration between the plume and background gas. This effective mixing length grows at a rate of $60 m/s. This fast mixing/mass penetration is largely due to the strong relative movement between the plume and the background gas. The molecular dynamics results agree well with the analytical solution in terms of relating various shock wave strengths.

Secondary shock wave in laser-material interaction

“…15 The shock wave phenomenon has also received much attention and recently has been explored in near-field laser material interaction, 16 as well as its dynamic structure and mass penetration under picosecond laser irradiation. 17 Although extensive experimental and theoretical work has been done on the shock wave in laser ablation, the formation of the secondary shock wave has not been explained satisfactorily. The objective of the present paper is to explicate the process of formation and particularly structure with thermodynamic and physical states of the secondary shock wave in nanoseconds range at molecular level.…”

“…Our current study shares the similar physical model as our established one, and the detailed description of the computational domain was given previously. [12][13][14][15]17 In brief, the physical target is placed in a gas environment and is irradiated by a laser pulse. The material is assumed to be argon crystal with an initial temperature of 50 K, where the background gas shares similar properties as the target, such as the molecular mass, but has a modified interatomic potential, which considers only repulsive force between atoms.…”

“…Computational details along with parameter specifications are provided in other literatures. [12][13][14][15][16][17][18] In our considerations, the spatial uniform single laser pulse irradiates the target top surface, with temporal Gaussian distribution and fluence of 5 J / m 2 . The laser pulse has 11.5 ps full width at half maximum and is peaked at 10 ps.…”

Molecular dynamics simulation of shock waves in laser-material interaction

“…N is the number of molecules/atoms confined by the affected region. Wang's previous simulations (Zhang and Wang, 2008) proved that the above stress boundary treatment works well in terms of eliminating stress wave reflection and avoiding undesired material damage in the boundary region.…”

“…In recent years, more emphases have been placed on the exploration of kinetic and physical properties of nanodomain shock wave in near-field laser material interaction (Feng and Wang, 2007) and its dynamic structure with mass penetration under picosecond laser irradiation (Zhang and Wang, 2008).…”