Optical Emission Spectroscopic (OES) Measurement is one of the most ideal plasma measurement methods, since it does not perturb the plasma. We would like to review various methods of OES measurement for processing plasmas in this tutorial course. First, we compare a couple of methods to diagnose processing plasmas with low-electron temperature and density, such as probe method, laser method, and OES method, and understand pros and cons of OES measurement. Then, we overview elementary processes to describe excitation kinetics in low-temperature plasmas. Next, we introduce collisional radiative (CR) model to describe number density of excited states based on the elementary processes. A method is presented to obtain electron temperature and density of plasmas based on the CR model. Next, we introduce a method to determine rotational and vibrational temperatures of electronically excited species of diatomic molecules like N2 or OH radicals in molecular gas-discharge plasmas. The rotational temperature could be useful to monitor an approximate value to the gas temperature of plasma in a state of non-equilibrium. Finally, we describe actinometry method that determines number density of atomic species, such as H, N and O, generated by dissociation reaction in molecular gas-discharge plasmas.
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