Determination of the non-relaxation (reflection) probability of metastable Ar(3P2) atoms on a Pyrex surface

Abstract

Two techniques allowing us to measure the probability for the non-relaxation of metastable atoms impinging on glass surfaces are presented. In the first one, the radial distribution of Ar*(3P2) metastable atoms in the proximity of the glass wall is determined by a resonant absorption technique in the afterglow of a low pressure (8.5 Pa) argon discharge. The comparison of the experimental density profile with model profiles predicted by a simple model, permits the determination of an upper limit, R ⩽ 0.45, for the non-relaxation probability. In the second experiment, the Doppler-shifted laser-induced fluorescence technique is used to deduce the velocity distribution function of Ar*(3P2) metastable atoms in the vicinity of a Pyrex wall in very low pressure (0.09–0.5 Pa) argon plasmas. The non-relaxation probability is deduced from the ratio of the flux of metastable atoms having their radial velocity oriented towards the cell axis to the flux of those with their radial velocity oriented towards the wall. This latter technique is much more precise and gives a value of R = 0.28 ± 0.05 for the non-relaxation probability. It is also shown that metastable atoms moving away from the surface have somehow been accommodated to the surface and acquired a velocity distribution corresponding to the wall temperature.