The temporal evolution in plasma potential during laser photo-detachment used to diagnose electronegative plasma

This is the authors' abstract. We don't add key points for this paper.

A floating emissive probe is applied in conjunction with pulsed laser photo-detachment of O − ions to enable measurement of the dynamic evolution in a plasma potential resulting from the presence of photoelectrons in a 13.56 MHz inductive radio-frequency oxygen discharge. The emissive probe emits thermionic electrons, allowing it to reach a saturation potential which is characterized as the local space potential of the plasma. After the photo-detachment pulse, the local space plasma potential in the illuminated region shoots up to a higher positive value and then relaxes to equilibrium in microsecond time scales. Using the relaxation time of the space potential, the negative ion temperature of O − is estimated over a 10–50 mTorr range and is found to be in the 0.19–0.03 eV range. The negative ion temperature measured by this method is found to be lower than that calculated from the time evolution in electron density resulting from photo-detachment which is independently measured using a resonance hairpin probe.