Experimental and computational investigation into the hydrodynamics and chemical dynamics of laser ablation aluminum plasmas

Laser ablation plasma chemistry is governed by a complex interplay between hydrodynamic plasma-gas mixing processes, thermodynamics, and rapid high-temperature chemical reactions. In this work, we investigate the gas-phase oxidation chemistry of ns-laser ablation aluminum plasmas in air using optical spectroscopy combined with advanced multi-physics modeling. Experimental measurements demonstrate the formation of AlO in the plasma plume as early as 1 mu s while computational results reveal that several AlxOy species are distributed in the periphery of the plume at even earlier times (<20 ns) in the presence of large temperature gradients and strong shockwaves. Interactions with the ablation crater during rapid plume expansion are shown to initiate vortex formation, followed by mixing dynamics that work to pull AlO into the vortices to react with gas-phase Al to form Al2O. Oxygen and several aluminum oxides are simultaneously pulled up through the stem of the fireball, encouraging further intermixing between reacting species and enhanced molecular formation. This work concludes that chemical dynamics in laser ablation plasmas is driven by diffusion processes, concentration gradients, and plume hydrodynamics while strong shockwaves generated during laser ablation do not impede chemical reactions.

Automated summary

Laser ablation plasma chemistry in aluminum plasmas is investigated using optical spectroscopy and multi-physics modeling. It is found that aluminum oxides are formed in the plasma plume due to temperature gradients and strong shockwaves. The interaction between the ablation crater and the plume leads to vortex formation and enhanced molecular formation. This study concludes that diffusion processes, concentration gradients, and plume hydrodynamics drive the chemical dynamics in laser ablation plasmas, and strong shockwaves do not impede chemical reactions.