TEMPORAL AND SPATIAL-DISTRIBUTION PROFILES OF LITHIUM ATOMS IN LOW-PRESSURE DISCHARGES BY CONCENTRATION-MODULATED ABSORPTION-SPECTROSCOPY

The application of the new pump-probe spectroscopic technique, COMAS ( concentration-modulated absorption spectroscopy), to the study of sput tered lithium atoms in two glow-discharge devices is discussed. Inform ation is presented on the absolute concentration of lithium atoms in a hollow cathode lamp (1.62 x 10(11) cm(-3) in the centre at 14 mA) and a plane-parallel de discharge (1.24 x 10(9) cm(-3) close to the catho de at 1.05 mA). In addition an experimentally derived absorption cross -section for the (2s)(2), S --> (2p)(2), P-1/2,P-3/2 resonance transit ion in lithium (a x 2.95 x 10(-12) cm(2)) is presented for the first t ime. In producing concentration profiles for both a commercial hollow cathode lamp and a glow-discharge system built in-house, use is made o f the high spatial resolution attainable with COMAS. Results obtained in the de plane-parallel system are compared to a theoretical model de scribing the transport of sputtered atoms through a low-pressure glow discharge. By varying the delay between the pump and probe laser pulse s, the lifetime of the (2p)(2), P-1/2,P-3/2 state has been measured as 25 +/- 1 ns showing good agreement with values obtained by other meth ods found in the literature (ca. 24-27 ns).