Chemical Dynamics of a Laser Microprobe Vapor Plume in a Controlled Atmosphere

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Abstract
The vapor plume produced by the action of a focused laser beam on a solid sample of an aluminum alloy or zirconium was studied in a controlled atmosphere. The formation of binary compounds by chemical reaction between the vapor plume and the atmosphere was followed with the use of emission, absorption, and fluorescence detection methods. Most experiments were performed at 150 Torr in 100% O2, 50% O2/50% Ar, and 100% Ar. Both spatially and temporally resolved profiles of the metal monoxide formed in the plume were recorded. The experimental data are compared to kinetic calculations for the formation of AlO and AlO2. The initial concentration of the atmospheric gas in the region of the plume was found to be less than the average bulk concentration in the sample chamber. A “piston” mechanism of plume expansion is proposed to account for this. Complete mixing of the plume with the atmosphere took at least 100 µs. A significant quantity of metal monoxide was formed in an atmosphere containing only trace amounts of oxygen. The sample is believed to be the source of oxygen.