Metastable atom density measurements in He and Ne positive column plasmas by an improved self-absorption method

An improved self-absorption method obtained from the parallel-beam modification of Harrison's method for measuring the metastable atom density in gas discharges has been proposed. This method has the advantage of high spatial resolution in measurement with a relatively simple apparatus. The metastable atom densities of He (2 1 S 0 and 2 3 S 1 ) and Ne (1s 3 and 1s 5 ) in the positive column plasmas have been measured using this improved self-absorption method by varying the gas pressure from 1 to 10 Torr and the discharge current from 10 to 50 mA. 'Constriction' of the radial metastable atom density distribution in neon plasma has been observed. All experimental results are given and discussed.