Mathematical Simulation of Plasma Expansion in Laser Shock Processing of Materials

摘要

Based on mathematical simulation, investigation of the special features of the expansion and transmission coefficients of an air plasma initiated by an Nd:YAG laser at either λ = 1.06|μm (IR action) or λ = 0.355 μm (UV action) in the wavelength range 1-20 GW/cm{sup}2 with a pulse length of 25-30 nsec has been made. The simulation allows one to conclude that the plasma expansion for the IR and UV action is significantly different. For the IR action the main expansion mechanism is fast propagation of an ionization wave toward the laser source. It is just the ionization wave that absorbs the major part of the laser radiation in this case. For the UV action, the plasma expands as a light-detonation wave, and is mainly influenced by relatively slow gasdynamic processes. The screening effect of the plasma can be characterized by its transmission coefficient. A sharp drop in transmission in 1-2 nsec is observed for the IR action, while for the UV action the decrease is nonmonotonic and takes 10-20 nsec.