Self-absorption method in combination with an optical probe: A possibility to determine the radial density profile of rare-gas metastables in low-temperature plasmas

Usually the self-absorption method is adopted to determine the metastable species density in a large number of low-temperature plasmas. In the previous works this method only gives an average metastable density from the line-integrated emission out of the plasma, assuming a uniform density profile. Instead, this work uses an optical probe immersed in the plasma. From the emission spectra measured at different positions, it is possible to obtain the actual metastable density profile. As an example, this technique is used to investigate an inductive Ar plasma at pressures 0.1-1 Pa. The spatial densities of Ar(1s₅) and Ar(1s₃) (in Paschen's notation) are experimentally determined, being in agreement with those predicted by a self-consistent collisional-radiative model published previously. Based on these results, application of the same method to the other kinds of rare-gas discharges is discussed.