Spatial measurements of neutral density depletion by two two-photon absorption laser laser-induced fluorescence spectroscopy (TALIF)

摘要

Neutral depletion in the diffusion chamber of a Helicon reactor is measured by spatially resolved laser-induced fluorescence spectroscopy with two-photon excitation (TALIF). Significant neutral depletion (～80 %) is obtained for moderate magnetic field, rf power and low pressure. Calculations of the plasma pressure and estimations of the neutral pressure, based on measurements of plasma density, electron temperature, and neutral density, indicate that significant gas heating takes place: Tg increases from 400 K at the edge to 1200 K in the centre of the discharge for a pressure of 11 mTorr, a magnetic field of 140 G and 500 W rf power. The effect of magnetic field, rf power and pressure on the neutral depletion is discussed.