Two-dimensional axisymmetric radiation hydrodynamics model of moderate-intensity nanosecond laser-produced plasmas

A two-dimensional axisymmetric radiation hydrodynamics model has been proposed to simulate nanosecond laser ablation of a solid target in ambient argon, air and helium at different pressures. The heat conduction equation used to simulate the conduction of laser deposition energy in the target and gas dynamic equations to describe the interaction between laser and vapor plasma and the evolution of plasma are coupled through the Knudsen layer relations at the target-vapor interface. A collisional-radiative model including 12 atomic processes is used to calculate the population of atomic energy levels and fractional ion abundance. The internal energy and pressure of the plasma are expressed by the equations of state based on a real gas approximation, which divides the internal energy into the ionization energy, thermal energy, and excitation energy of atoms and ions. The distributions of the temperature, pressure, density and velocity of the target and plasma are calculated by using this model, and the results are analyzed. Experimental results of multiple diagnostic tools including fast photography, shadowgraphy images, spatio-temporally resolved optical emission spectroscopy and laser interferometry, are used to benchmark the simulation results, and satisfactory consistencies are obtained. The model provides a numerical tool to interpret experimental data of a moderate-intensity nanosecond laser ablated solid target when the temperature of the target surface does not reach the critical value.