Photodetachment effect in a radio frequency plasma in CF4

Experiments to study negative ion densities have been carried out using the photodetachment effect in a rf plasma in CF4. Electrons are detached from the negative ions under the influence of the pulse of a Nd:YAG laser. The induced increase of the electron density is measured as a function of time using the shift of the resonance frequency of a microwave cavity containing the plasma. The negative ion density [F-] is found to be about (4±1)×1015 m-3, a factor 4±1 higher than the electron density