Detection Technique of Negative Ions by Photodetachment in SF6 Low-Frequency Discharge

For the photodetachment, an optical system with dielectric multilayer mirrors was used to effectively irradiate an N2 laser pulse to the discharge space. At a phase of 30 kHz applied voltage just before the discharge current rapidly rises, and at a distance of 5 mm from the grounded electrode with a positive polarity in the SF6 discharge of 0.76 W at 0.2 Torr, the negative ion density measured is of the order of 108 cm-3.