Collisional radiative model in argon for laser-induced fast-ionization wave

Abstract

A laser-induced fast-ionization wave (FIW) is the post laser-breakdown phenomenon observed when laser intensity is 1013 W m−2 in atmospheric pressure. Its propagation velocity exceeds 10 km s−1. The discharge structure has similarity with streamers and sprites. An earlier study demonstrated that the velocity of the FIW is proportional to the laser intensity. The electron temperature and density in the FIW were found using emission spectroscopy. In this study, a collisional–radiative model with 79 levels of atomic population was developed to investigate the dynamics of excitation population density and the neutral particle temperature in a FIW. Using the gas temperature-dependence of the depopulation frequency for energy level p = 5 (4s′[1/2]1), the reasonable neutral particle temperature at the front of FIW is obtained by comparing experimentally observed spectra in the fine structure of 4s–4p.