Abstract
Highly sensitive detection of neutral Kr atoms was accomplished by the use of laser-induced fluorescence. In one experiment, Kr at 40 parts per 1012 in He was detected at a signal-to-noise ratio of 500 by time-resolved fluorescence measurements. The Kr metastable 1s 5 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 resonance fluorescence became negligible, trace quantities of Kr were detected by the use of a pulsed-laser pumping scheme. In a related experiment, 78Kr/86Kr 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 86Kr metastable population was selectively depleted by optical pumping to a higher-lying state that relaxed to the ground state by means of radiative cascade. After the 78Kr/86Kr ratio of metastables had been enriched by a factor of 10, the 78Kr population was probed by pulsed excitation. Premixed 78Kr/86Kr ratios were measured to within an accuracy of 10%, even for unresolved, Doppler-broadened transitions.
© 1995 Optical Society of America
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