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

A plume consisting of vapour and ionized particles of the workpiece is usua lly formed during various types of laser materials processing. The characte ristics of this plume depend on a large number of parameters such as the la ser 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 temper ature of the melt pool and the vaporization rate are also calculated on the basis of the Stefan condition at the liquid-vapour interface. The absorpti on coefficient of the plasma given by the Kramers-Unsold relation and the i onization fraction given by the Saha-Eggert equation are used to model the laser beam propagation through the plasma. A detailed analysis of the plasm a stability indicates that absorption of the laser beam by the plasma affec ts the melt-pool surface temperature nonlinearly.