Rigorous theoretical analysis of the continuous wave optogalvanic effect in the neon positive column

A rate-equation model with greatly improved quantitative rigour is detailed for the CW optogalvanic effect on the 1s-2p transitions of neon atoms in t he positive column of a de normal glow discharge. This work constitutes one part of a wider complementary programme which also includes CW laser colli sionally-induced fluorescence, optical emission spectroscopy and optical ab sorption spectroscopy for the excited-state populations, all employing the same atomic and discharge data set. Our aim has been to produce a theoretic al model and test it with stringently collected data, to demonstrate that t unable laser CW optogalvanic spectroscopy (OGS) can provide a truly quantit ative diagnostic of the excited-state kinetics in low-temperature discharge s. The model is deliberately restricted to just six essential perturbed rat e equations, four for the Is states, one for the charged particles and one for the discharge current. Our formulation, via the 1s and 2p CW-induced pu mp rate perturbations, allows very direct identification of the important e xcited-state kinetics producing the OGE. The principles and scope of our th eory are demonstrated for a neon filling pressure of 2.0 Torr and currents of 1-10 mA, based on fitting the model for three carefully selected transit ions, the 1s(5)-2p(4) (594.5 nm), 1s(4)-2p(4) (609.6 nm) and 1s(5)-2p(9) (6 40.2 nm). Results show that the magnitudes of the CW optogalvanic effect on the 1s-2p transitions are strongly dependent on the discharge pumping rate s of the 1s states and their coupling, and confirms that cascade effects mu st be included in the 1s excitation rate coefficients.