Modeling Microsecond Timescale Molecular Formation in Laser Ablated Plasma Plumes*

In recent years, laser ablation has seen increased use as an analytical tool for studying the chemical kinetics of metallic vapor in reactive atmospheric environments, primarily using laser induced breakdown spectroscopy (LIBS). However, interpretation of LIBS experiments is often hampered by the transient and nonuniform nature of the plasma plume expansion, which includes mixing and complex inner plume dynamics. Here, we present a one-way coupled model that connects early timescale (nanosecond) laser deposition and shock expansion physics to longer timescale (microsecond) plume evolution dominated by multispecies diffusion and chemical reactions. The initial expansion is compared to high-resolution optical plume imaging and time of flight measurements, while later molecular formation is compared against various literature studies. Aluminum ablation in air is used as the primary validation target, but other target materials are also discussed.