Influence of evaporation on the melt behavior during laser interaction with metals

A theoretical investigation is made of the behavior of a melt on whose surface laser radiation with a homogeneous intensity distribution is absorbed. A dispersion equation is obtained for the hydrodynamic perturbations, taking into account the vaporization pressure, thermocapillary forces, and melt viscosity. The vaporization pressure is shown to lead to an instability of the melt surface. This effect differs qualitatively from an instability of a plane sublimation front which arises only for bulk absorption of laser radiation. The time needed for the hydrodynamic instability to develop decreases rapidly with increasing temperature of the illuminated surface and become less than a millisecond when the vaporization pressure reaches 0.1 bar.