Measurements of negative ion density in high-density oxygen plasmas by probe-assisted laser photodetachment

Abstract

Probe-assisted laser photodetachment has been developed and applied to measure the negative ion density (n−) in high-density plasmas. Temporal variation of n− is obtained in high-density and low-pressure oxygen plasmas generated by helicon wave excitation. Negative ions are not observed in the active discharge phase and rapid increase of n− is seen only in the afterglow phase. This efficient production of negative ions is considered to be due to dissociative electron attachment to metastable molecular states, O2M(A3Σu+, A′3Δu, and c1Σu−), located at 4–5 eV above the ground state.