Detection of low lead concentrations by laser-excited atomic fluorescence

An investigation was made of the feasibility of detecting extremely low $Pb$ concentrations by laser-excited atomic fluorescence. Lead was selected as an example of a three-level atomic system with an intermediate metastable level. Accumulation of atoms in the metastable level resulted in a sharp decrease in the number of fluorescence photons emitted by a single atom in a strong resonance field compared with that found in twolevel atomic systems such as $Na$. As a result, the threshold for observation of extremely low concentrations of atomic vapor increased substantially. Lead atoms were excited by the second harmonic of a pulsed dye laser at a wavelength of 283.3 nm and fluorescence was recorded at 405.8 nm. A detection limit in accordance with the $3\sigma$ criterion of 250 atoms/cm${}^3$ or 30 atoms per analytical volume was achieved. Possible methods of improving the sensitivity are discussed.