Laser plume temperature measurements in various gases

Nd-YAG laser plume temperatures of 3000--5400K were measured on 304 stainless steel and 1100 Al in various gases using emission spectroscopy. Temperatures were higher in the reactive gases air, 02, and SF6, compared to inert gases. Ionic spectra were not observed, indicating that the plume primarily consists of hot vapors and does not contain a plasma, in contrast to CO/sub 2/ laser processing in which plasmas have been observed. The plume temperature remained constant with changes in laser power and with time during the duration of the laser pulse. Light emissions from the plume and from the cooling weld pool after the laser pulse was off were measured and correlated with melt depth. 7 refs.