EXPERIMENTAL STUDY OF THE LASER INDUCED PLASMA IN WELDING CONDITIONS WITH CONTINUOUS HIGH POWER CO2 LASERS

It is well known that the metallic plasmas observed in laser welding play an important role in energy transfert during laser materials processing. They are critical to understanding energy transport to the workpiece. This paper reports an experimental investigation characterizing the plasma using visible emission -spectroscopy. These experiments provided the electron density and temperature distributions (~1017 cm-3 and 6000-7000 °K). The experimental data are then used to determine laser attenuation and refraction as the beam propagate through the plasma column. These results are compared with direct absorption measurements where an integrating spere has been used, and with a numerical simulation. It was observed that the absorption coefficient is closely correlated to the spatial and temporal behaviour of the plasma and the effect of refraction is of primary importance for laser processing when using other gases than helium at high laser intensity