Complementary optical diagnostics for determination of rate coefficients and electron temperatures in noble gas discharges

Abstract

We utilize an array of related optical diagnostics to deliver quantitative description of each process involving the 15 lowest levels in neon, for reduced electric fields ranging from 3×10-16 to 2×10-16 V cm2 (3-20 Td). Description of the kinetics between the 1s and 2p excited states (Paschen notation) has been obtained using CW laser collisionally induced fluorescence (i.e. fluorescence from a non-excited upper level). We have employed this technique in combination with the traditional optical emission and absorption spectroscopic studies to determine the rate coefficients describing electron-collisional excitation from the ground to the 1s and 2p states. These values, along with previously determined 1s-2p rate coefficients, have been used with current literature cross sections to provide information on the electron distribution function for energy bands of 2-8, 16.9-23.0 and 19.0-25.5 eV. Values of the electron temperatures obtained from our 1s coefficients were used for an extensive study of the ground state to 1s excitation functions. From 3 to 20 Td, the average values of the temperature corresponding to the 1s excitations ranged from 1.8 to 3.1 eV, while those from 2p excitation were in the range 1.6-2.9 eV. Our investigation of the bulk temperature using data for 1s-2p excitation suggests a scaling of ~0.5 for the published theoretical excitation function, which is supported by the new experimental cross sections of Boffard et al. A quantitative description of cascade to the 1s states is also presented, showing that at the top of our reduced field range, cascade from the 2p states contributes 29-35% of the total excitation rates from the ground state.