TRACE DETECTION OF KRYPTON USING LASER-INDUCED FLUORESCENCE

Highly sensitive detection of neutral Kr atoms was accomplished by the use of laser-induced fluorescence. In one experiment, Kr at 40 parts per 10(12) in He was detected at a signal-to-noise ratio of 500 by tim e-resolved fluorescence measurements. The Kr metastable Iss level was populated by cascade after two-photon excitation to the 2p(6) level by the frequency-tripled output of a pulsed single-longitudinal-mode dye laser. After a delay, when scattered laser light and cascade resonanc e fluorescence became negligible, trace quantities of Kr were detected by the use of a pulsed-laser pumping scheme. In a related experiment, Kr-78/Kr-86 isotope ratios ranging from 1 to 0.1 were measured with a resonant isotopic depletion technique first proposed by Makarov [Sov. J. Quantum Electron. 13, 722 (1983)]. The Kr-86 metastable population was selectively depleted by optical pumping to a higher-lying state t hat relaxed to the ground state by means of radiative cascade. After t he Kr-78/Kr-86 ratio of metastables had been enriched by a factor of 1 0, the Kr-78 population was probed by pulsed excitation. Premixed Kr-7 8/Kr-86 ratios were measured to within an accuracy of 10%, even for un resolved, Doppler-broadened transitions.