Temporal analysis of laser-induced plasma properties as related to laser-induced breakdown spectroscopy

The evolution of a laser-induced plasma is characterized in terms of its temporally resolved spectral absorptivity, spectral emissivity, and free electron density via Stark broadening during the first few hundreds of nanoseconds. Transmission measurements using 532 and 1064 nm probe laser beams reveal near opacity of the laser-induced plasma at times corresponding with the tail end of the plasma creating laser pulse. This temporal region is coincident with the maximum free electron density greater than 10¹⁸ cm ^-3. At times approaching 500 ns following plasma initiation, the plasma absorptivity diminishes markedly, rendering the plasma essentially transparent to incident radiation. The fundamental change from an absorbing (i.e. optically thick) plasma to a non-absorbing plasma during this period is important with respect to the radiative transfer within and from the plasma. Overall, these phenomena play important roles in the evolution of the laser-induced plasma and the technique of laser-induced breakdown spectroscopy.