Observation of Calcium Atomic Fluorescence in Laser-Induced Plasma with High Spatial Resolution

Optimum experimental parameters for studying distribution of calcium atoms in laser-induced plasma at low pressure (16 Torr) by means of atomic fluorescence are determined. The scheme of nonresonant fluorescence based on transitions between 4 s 4 p ( 3 P °)–4 p 2 ( 3 P ) states at 428.30 and 430.25 nm is proposed and implemented for excitation and observation of fluorescence for the first time. Based on analysis of the influence of crater deepening on intensity of fluorescence signal and comparison of fluorescence saturation curves, we demonstrate that a pure calcium carbonate is preferable as a target for observation of fluorescence. Substantial (by a factor of 62) enhancement of the fluorescence signal under optimum conditions allows neglecting the contribution of spontaneous emission to line intensities. We also demonstrate that temperature has low impact on population of the level used for excitation of fluorescence in the temperature range observed in the laser-induced plasma. These circumstances allowed spatially measurements to establish the lateral distribution of calcium atoms in plasma after optimization of parameters.