Nonlinear effects of laser-plasma interaction on melt-surface temperature

A plume consisting of vapour and ionized particles of the workpiece is usually formed during various types of laser materials processing. The characteristics of this plume depend on a large number of parameters such as the laser power, spot size, scanning speed, material properties and shielding gas. The height, radius, temperature and absorption coefficient of the plasma are calculated for various values of process parameters. The surface temperature of the melt pool and the vaporization rate are also calculated on the basis of the Stefan condition at the liquid-vapour interface. The absorption coefficient of the plasma given by the Kramers-Unsold relation and the ionization fraction given by the Saha-Eggert equation are used to model the laser beam propagation through the plasma. A detailed analysis of the plasma stability indicates that absorption of the laser beam by the plasma affects the melt-pool surface temperature nonlinearly. (author)