Level populations in a laser-induced plasma on a lead target

Time-resolved measurements of the intensity variation of five lead atomic lines at 357.275, 363.958, 367.151, 368.348 and 373.994 nm along the height of a laser-induced breakdown spectroscopy (LIBS) plasma on a solid target at standard atmospheric conditions were made. After background correction, peak stripping of the 367 and 368 nm lines and integration over the line profiles, the temporal and spatial development of the populations of the levels from which the five lines originate were calculated. The spatial and temporal population distributions indicated that these levels were not under equilibrium conditions with respect to one another for the majority of measurements. Spatial and temporal excitation temperatures of the order of 14 000 K were obtained from Boltzmann plots, but the validity of these values should be treated with skepticism in light of nonequilibrium thermodynamic conditions.