A perturbed steady-state rate-equation model has been developed for the cw laser collisionally induced fluorescence (LCIF) produced by excitation on one of the 1s-2p noble gas transitions. This work is one part of a wider complementary modeling program which includes cw optogalvanic spectroscopy, optical emission spectroscopy, and optical absorption spectroscopy, with the overall aim of testing all of these models with the same stringently assembled atomic and discharge data set. Our aim here is to demonstrate the principal features of our cw LCIF model by using it to describe our experimental observations produced by pumping transitions originating on the 1s(5) metastable and 1s(4) resonance states of neon atoms in the positive column of a normal glow discharge at 2.0 Torr and a discharge current of 5 mA. The model shows that these cw LCIF spectra are dominated by 1s-2p excitation and electron collisional coupling among the 2p states. We show that the model allows us to quantify explicitly the various individual contributions to each line in the cw LCIF spectra. The theory and analyses presented here apply equally well to other noble gases and we believe can be modified appropriately for trace noble gases in atomic-molecular mixtures.

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 the positive column of a dc normal glow discharge. This work constitutes one part of a wider complementary programme which also includes CW laser collisionally-induced fluorescence, optical emission spectroscopy and optical absorption spectroscopy for the excited-state populations, all employing the same atomic and discharge data set. Our aim has been to produce a theoretical model and test it with stringently collected data, to demonstrate that tunable laser CW optogalvanic spectroscopy (OGS) can provide a truly quantitative diagnostic of the excited-state kinetics in low-temperature discharges. The model is deliberately restricted to just six essential perturbed rate equations, four for the 1s states, one for the charged particles and one for the discharge current. Our formulation, via the 1s and 2p CW-induced pump rate perturbations, allows very direct identification of the important excited-state kinetics producing the OGE. The principles and scope of our theory 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 transitions, the 1s5 -2p4 (594.5 nm), 1s4 -2p4 (609.6 nm) and 1s5 -2p9 (640.2 nm). Results show that the magnitudes of the CW optogalvanic effect on the 1s-2p transitions are strongly dependent on the discharge pumping rates of the 1s states and their coupling, and confirms that cascade effects must be included in the 1s excitation rate coefficients.

We describe a method for the determination of rate coefficients for collisional excitation out of the 1s states of a noble gas using continuous-wave laser collisionally induced fluorescence (CW LCIF, i.e. fluorescence from an upper level which is not that of the laser transition). The intensity of CW LCIF lines from an upper 2p level that is strongly coupled to an influential 1s level is dominated by the electron collisional rate out of that level. By an appropriate choice of LCIF line we fit our recently published theory to experimental observations to determine a set of electron collisional direct 1s mixing and 1s-2p excitation rate coefficients. The values of coefficients determined in this way show very good agreement with those which have been calculated using cross section data from the literature with the measured electron temperature. For cases where accurate cross section data are available for the 1s-2p transitions CW LCIF diagnostics should, via these rate coefficients, provide reliable values of the bulk electron temperature.

We present a method for determining the 2p (in Paschen notation) collisional excitation transfer coefficients in noble gases using continuous-wave laser collisionally induced fluorescence (CW LCIF, i.e. fluorescence from an upper level which is not that of the laser transition). The technique requires isolation of the specific 2p coupling process under examination, whereby that process provides an important and quantifiable contribution to the LCIF. This is achieved by selecting appropriate laser excitation and LCIF transitions. For a neon discharge operating at pressures ranging from 1.5 to 8.0 Torr and currents from 1 to 10 mA, 2p coupling is by ground-state atom collisions and the largest coupling exists between adjacent states. We show that in certain cases excitation transfer plays an important role in the excited-state kinetics.