Measurements of the neutral and ion density under the antenna in a helicon source*

Using confocal laser induced fluorescence (LIF), argon neutral and ion velocity distribution functions (N/IVDFs) are measured in inductively coupled and helicon mode plasmas. Velocity distributions in these plasmas provide insight into the ionization processes in the helicon antenna region and a measure of the total ionization efficiency of the helicon source. LIF has been used to measure these processes in past studies. However, the use of confocal optics to measure the relative metastable state densities directly under the helicon source antenna demonstrates the advantage of employing confocal optical systems in sources with limited optical access.