Elementary processes of atmospheric-pressure molecular gas discharge plasmas in non-equilibrium state and their diagnostics with OES

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We review fundamentals of optical emission spectroscopy (OES) of plasmas of atmospheric pressure and, in particular, its applications to processing plasmas. Collisional radiative model is described to understand the excitation kinetics and population distributions of excited states in order to examine the electron temperature and density. It is shown that corona equilibrium is often adopted as justifiable assumption of excitation kinetics for general processing plasmas. Line intensity measurement methods are studied for atmospheric-pressure Ar plasma and low-pressure N2 plasma. Population densities of excited states of argon atoms are theoretically examined for ionizing argon plasma in a state of non-equilibrium under atmospheric pressure from the viewpoint of elementary processes with collisional radiative model. The dependence of excited state populations on the electron and gas temperatures is discussed.