On the high argon metastable atom density measured near the cathode surface of a hollow cathode discharge

Abstract

We report laser absorption measurements of spatial density distributions of Ar metastable (Arm) and resonant state atoms in a cylindrical hollow-cathode discharge (HCD). The evaluation of the measured data by standard analysis indicates high Arm densities near the walls of the HCD. To obtain convincing evidence for these high densities, we critically examine the effect of diffraction phenomena on the measured distributions. This analysis confirms that—while diffraction has a significant effect—the Arm densities near the cathode wall are in the 1016 m−3 range. The measured values suggest that, in addition to the discharge volume, metastable atoms are likely to be created at the surface of the cathode. Further investigation is needed to clarify the processes responsible for the observed behavior.