Toward the Use of Surrogate Post-Detonation Gas Mixtures to Study Aluminum Laser-Induced Plasma Chemistry

Metals under high-energy nanosecond laser excitation undergo ablation, phase explosion, entrainment, and subsequent reaction in the extreme environment of a laser-induced plasma where ionization levels, excitation temperatures, and instantaneous pressures are high. In this study, we illustrate the reactions of aluminum (Al) under different detonation-relevant atmospheric conditions. We control the environment within a small-scale vacuum chamber using dynamic gas mixing techniques and use mixtures representing equilibrium state gas compositions predicted by thermochemical code following the detonation of several common explosives. We probe the environmental effects using schlieren imaging to track the laser-induced shock wave and gated, high-resolution mid-to-near ultraviolet and visible spectroscopy at the hundreds of nanosecond to tens of microsecond timescale to track reaction species. Enhancement of plasma properties (e.g., electron density, ionization ratio) and stochastic behavior in the laser-induced shock velocity with the presence of argon is observed. A matrix of comparisons among plate and powder Al, detonation gas mixture content, and temporal evolution behaviors is broadly characterized and cataloged. These experiments help us understand the reactions of Al in anaerobic plasma environments generated from detonations in a microscale high-throughput way.