Energy loss in the plasma during laser drilling

A plume consisting of vapour and ionized particles from the workpiece is commonly formed during various types of laser materials processing. The process parameters such as the laser power, spot diameter, scanning speed, material properties and shielding gas affect the properties of the vapour-plasma plume. A mathematical model is presented in this paper to predict the plasma 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 condition at the liquid-vapour interface. A new experimental technique named as the pinhole experiment is presented in this paper to measure the partitioning of laser energy between the plasma and the workpiece. Workpiece material: stainless steel foil.