Atomic Hydrogen density and temperature measurements by Two-Photon Absorption Laser Induced Fluorescence in a High Power Density H2/CH4 Microwave Plasma

In the context of monocrystalline diamond plasma deposition, the atomic hydrogen densities and temperatures have been determined by two-photon absorption laser induced fluorescence in a H2/CH4 microwave plasma at high pressure (>200 mbar) and high microwave power (>2000 W). Absolute H densities were obtained by a calibration method that consists in measuring the TALIF signal emitted from Kr gas at a well-known pressure. H temperatures were estimated from Doppler broadening of the absorption line. In plasmas containing 1% CH4, the measured H densities and temperatures in the plasma bulk are in the ranges 1-3x1017 cm-3 and 3000-3500 K respectively. As the pressure rises from 200 mbar to 400 mbar, the maximum H density increases and shifts closer to the substrate, and the H molar fraction and H temperature increase in the plasma bulk.