Plasma arising during the interaction of laser radiation with solids

The physical phenomena which result in the appearance of plasma near the surface of a solid heated by laser radiation are described. They include: the dynamics of heating and vaporization of the solid surface as a whole; separate defects of the surface, and aerosol particles; the hydrodynamics of the expansion of the vaporized material into the gas surrounding the target; and, the kinetics of ionization in the vapors or in their mixture with the surrounding gas. Plasma formation is linked, first, to the necessity of having sufficiently high vapor density in the interaction zone or to heating of the target up to a definite temperature, which imposes definite requirements on the energy parameters of the laser pulse. It is also linked to the possibility of development of ionization in the vapors or their mixtures with the surrounding gas; this dictates a definite laser-pulse intensity. Starting from these requirements, the boundary of the plasma region is found in the energy-intensity plane. The moment at which plasma appears is determined as the point of intersection of this boundary by the laser pulse in the same plane. Different cases of plasma formation in diffusion and hydrodynamic regimes of vapor efflux, associated with heating and vaporization of the target as a whole and its microdefects or aerosol particles, are described on the basis of this approach for different materials, pressures, and composition of the gas surrounding the target, size of the focusing spot, and durations, shapes, and wavelengths of the laser pulses.