| A diode laser-based laser-induced fluorescence (LIF) diagnostic has been developed that can measure three species; argon neutrals, argon ions, and helium neutrals. This diagnostic has been combined with passive emission spectroscopy and a neutral argon collisional-radiative (CR) model to measure ground state radial density profiles of argon atoms in a helicon source. We have found the ground state neutral argon atoms to have a 60% on-axis depletion for a typical helicon mode case, yielding a 28% ionization fraction. The depletion decreases to 20% with a 9.8% ionization fraction for a second helicon mode case, indicating that slight changes in plasma parameters can lead to a significant difference in RF power coupling and gas ionization. In a series of experiments in a low density helicon source, measurements of argon ion flow through a double layer with the LIF diagnostic confirmed predictions of a Monte-Carlo particle-in-cell model of double layer formation in expanding helicon plasmas. Additionally, the LIF diagnostic has been used to measure argon neutral flow velocities, argon ion flow velocities, and argon neutral density and temperature evolution during a plasma pulse. |
