The analysis of nonequilibrium phenomena during laser action on metal vapors

In this paper the laser radiation of moderate intensity $G=10^6\div10^{10}$ Вт/см${}^2$ and wavelength $\lambda=1.06$ $\mu m$ and the metal vapors interaction is investigated by means of mathematical modeling. For modeling the collision – radiational model describing kinetics of nonequilibrium ionization and recombination is used. The modeling has shown, that the laser radiation and metal vapors interaction can go on in the two qualitatively different regimes: without or with the optical breakdown.
If the irradiation is prolonged enough but its intensity is deficient to induce the avalanche ionization, the system come into the steady state, characterized by the thermodynamic equilibrium, and the lack of equilibrium between the vapors and laser radiation.
Optical breakdown for vapors of different metals is the essentially nonequilibrium transition state from partially ionized vapor to the fully ionized plasma, in which coulomb collisions are dominated. The investigations have shown that optical breakdown has explicit threshold on radiation intensity. When using the macroscopic description of breakdown the threshold values of intensity depend on the ionization potential, the structure of electron excitation levels of neutral atoms and the initial temperature of evaporated substance and the irradiation duration as well.