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

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 60m/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. [DOI: 10.1143/JJAP.47.964]