Negative ion density determination using probe to detect photo-detached electron by continuous wave laser

Theoretical calculation of probe current increase caused by photo-detachment of electrons by laser irradiation in a plasma and experimental studies have been done in order to determine the absolute negative ion density. The positive column of a hollow cathode DC Ar:O-2 discharge is used in the experiment. During laser irradiation of the anode, detected photo-detached electron current increases with increase of the laser on-off frequency because of temporal space potential change. The O- densities determined from the theoretical calculation show good agreement with those theoretically predicted based on Ichikawa's theory when the laser does not irradiate the anode.