Measurement of Fokker-Planck Diffusion with Laser-Induced Fluorescence

Laser-induced fluorescence in plasmas is shown to be strongly influenced by velocity-space diffusion, under the proper conditions. The induced fluorescence is modeled by a set of coupled rate equations that include the Fokker-Planck operator for each state density, and the results are compared with data from a gas-discharge plasma in which the ArII $({3d}^{\prime }{)}^2{G}_{9/2}$ metastable state is optically pumped. The Fokker-Planck diffusion coefficient $D$ is determined and found to be in agreement with theory.