Diagnostics of high-pressure arc plasmas from laser-induced fluorescence

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Abstract
Laser-induced fluorescence has been studied in high-pressure mercury, mercury-metal halide and sodium-mercury arcs, using a rhodamine 6G CW dye laser for the excitation. The fluorescence was observed at 90 degrees with respect to the laser beam. The fluorescence is interpreted assuming thermal equilibrium in the excited region of the arc. Quantitative evaluation of the fluorescence from the mercury arc indicates the validity of this approach. Laser-induced fluorescence can be used to determine local density ratios of arc plasma components and local emission profiles (line shapes and line shifts). As an application the electron density and the Na-Hg density ratio at the arc axis of a sodium-mercury discharge are determined from Stark shifts in the fluorescence of several transitions in the sodium atom and from fluorescence intensities.