Airborne-mercury detection by resonant UV laser pumping

Optical pumping of the Hg0 (6s 1S0 → 6p3P1) transition at 253.7 nm (in air) leads to extremely fast energy transfer and strong laser-induced-fluorescence (LIF) from the Hg0 (7s 3S1 → 6p 3P2) green transition at 546.2 nm, which is not directly populated by the laser. Ionization occurs simultaneously and becomes particularly strong at reduced background pressures. These observations are consistent with the existence of a multiphoton process followed by electron collisional excitation. Preliminary studies are made to evaluate these phenomena for detecting elemental airborne mercury by LIF and point monitoring with an ionization detector. Measured sensitivities of 2 and 10 parts in 109 (ppb), respectively, at 0.1-Torr air pressure are projected to increase to 1 × 10-4 and 1 × 10-5 ppb after relevant system optimization. © 1997 Optical Society of America.