Analysis of laser ablation: contribution of ionization energy to the plasma and shockwave properties

By fitting simulation results with experimentally measured trajectories of the shock wave and the vapor∕background gas contact surface, we found that inclusion of ionizationenergy in the analysis leads to a change in the evolution of the pressure, mass density, electron number density, and temperature of the vapor plume. The contribution of ionizationenergy to both the plasma and shock wave has been neglected in most studies of laser ablation. Compared to previous simulations, the densities, pressures, and temperatures are lower shortly after the laser pulse (< 5 ns), but become larger (by a factor of 2) as the time after the laser pulse increases (> 50 ns). The predicted laser energy conversion ratio also showed about a 20% increase (from 35% to 45%) when the ionizationenergy is considered. The changes in the evolution of the physical quantities result from the retention of the ionizationenergy in the vapor plume, which is then gradually transformed to kinetic and thermal energies. When ionizationenergy is included in the simulation, the vapor plume attains higher expansion speeds and temperatures for a longer time after the laser pulse. The better determination of the temperature history of the vapor plume not only improves the understanding of the expansion process of the laser induced vapor plume but also is important for chemical analysis. The accurate temperature history provides supplementary information which enhances the accuracy of chemical analysis based on spectral emission measurements (e.g., laser induced breakdown spectroscopy).