Plasma formation threshold in a vapor–gas mixture on the surface of a laser-heated metal

An analysis is made of the interaction of laser radiation with metals in the absence of intense vaporization and surface damage when the surface temperature does not exceed the boiling point of the target material at given pressure of the surrounding gas and a diffusion-formed mixture of the target vapor and the surrounding gas appears near the target. Simple formulas are obtained for the threshold values of the intensity and energy of a laser pulse at which breakdown occurs first in the vapor of the target material and then in the surrounding gas. Dimensionless coordinates are proposed for the laser radiation intensity and the energy per unit area, and the regions of plasma formation are constructed. In these coordinates the regions are universal and are weakly dependent on the nature of the surface material and surrounding gas. The threshold values obtained from the formulas are compared with experimental data.