Thermal effects mediating the flow induced by laser-induced optical breakdown

Abstract

Laser-induced optical breakdown is a nonintrusive, versatile means of depositing energy in a gas, though the laser-generated flow can be complex, and its coupling with the plasma dynamics is not fully understood. By comparing nonequilibrium-plasma, equilibrium-chemistry, and frozen-gas models, our simulations show that rapid heat release by electron recombination enhances the supersonic expansion of the plasma. The resulting shock wave leaves behind a vortical flow whose strength is suppressed by the high thermal conductivity of free electrons. These results indicate that, while thermal nonequilibrium is weak, chemical nonequilibrium is needed to accurately predict post-breakdown flow.