Application of Laser Fluorescence Spectroscopy by Two-Photon Excitation into Atomic Hydrogen Density Measurement in Reactive Plasmas

Abstract

Density profiles of hydrogen atoms in reactive plasmas of hydrogen and methane gases were measured, for the first time, using the laser fluorescence spectroscopy by two-photon excitation of Lyman beta transition and observation at the Balmer alpha radiation. Absolute density determinations showed atomic densities of around 3×10¹⁷ m^-3, or the degree of dissociation to be 10^-4. Densities along the axis perpendicular to the RF electrode showed peaked profiles, which were due to the balance of atomic hydrogen production by electron impact on molecules against diffusion loss to the walls.