Energy loss in the plasma during laser drilling

A plume consisting of vapour and ionized particles from the workpiece is co mmonly formed during various types of laser materials processing. The proce ss parameters such as the laser power, spot diameter, scanning speed, mater ial properties and shielding gas affect the properties of the vapour-plasma plume. A mathematical model is presented in this paper to predict the plas ma properties, such as its temperature and absorption coefficient, and the partitioning of laser energy between the plasma and workpiece for different process parameters. The effect of plasma on the surface temperature of the liquid metal and the vaporization rate are modelled using the Stefan condi tion at the liquid-vapour interface. A new experimental technique named as the pinhole experiment is presented in this paper to measure the partitioni ng of laser energy between the plasma and the workpiece.