Saturated laser-induced fluorescence in a high-pressure metal halide discharge

Abstract

Local measurements of the saturated laser-induced fluorescence (LIF) signal from pulsed laser excitation of the 6 3 P1 resonance state of Hg have been obtained in a high-pressure metal halide lamp. Hg atoms were excited at 436 nm (6 3P1 →7 3S1 ) and the laser-induced fluorescence was detected at 546 nm (7 3S1 →63P2 ). The LIF signals were obtained as a function of radial position and the ac phase angle. The LIF signals were corrected for the optical depth of the fluorescence. The LIF measurements were made under saturated conditions to minimize the spatial dependence of the fluorescence quantum efficiency in the discharge. The 6 3P1 density was a maximum at the arc center and monotonically decreased towards the wall. The relative 6 3 P1 profile was broader at the current zero crossing than at the current maximum. The 6 3 P1 density was undermodulated during the ac phase at the arc center compared to predictions based on the Hg 577-nm emission, suggesting a departure from local thermodynamic equilibrium. At a reduced radius of 0.62, the 6 3 P1 density was almost independent of phase angle. Estimates of the 6 3 P2 density were obtained from the optical depth. LIF measurements were also obtained by exciting the 6 3P2 level of Hg at 546 nm and detecting the fluorescence at 436 nm. The spatial and phase angle dependence of the LIF signals from a mercury discharge were very similar to the results from a metal halide lamp.