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David Steuer, Henrik van Impel, Andrew R. Gibson, Volker Schulz-von der Gathen, Marc Böke, Judith Golda

• A new actinometry approach, helium state enhanced actinometry (SEA), is presented. This diagnostic uses the emission of the atomic states O(3P\(^{3}\)P) (\(\lambda\) = 844.6 nm), Ar(2p\(_1\)) (\(\lambda\) = 750.4 nm) and He(3\(^{3}\)S) (\(\lambda\) = 706.5 nm) and allows the atomic oxygen density and the mean electron energy to be determined simultaneously from the spectral line intensity ratios. Here, the atomic states are selected in a way that they cover a wide range of the electron energy distribution function (EEDF). The method is compared to the classical actinometry approach and energy resolved actinometry (ERA) based on measurements on the COST microplasma jet. In addition, a benchmark against two-photon absorption laser induced fluorescence measurements is performed. Both atomic oxygen densities and mean electron energies are in good agreement with the literature. Furthermore, SEA offers a number of advantages over known approaches. Firstly, the experimental complexity is significantly reduced by using time-integrated spectra instead of phase-resolved measurements, as used in the original ERA approach. Secondly, the precision of the electron energy measurement can be significantly improved by the use of the helium state. In addition, known uncertainties e.g. due to excitation of oxygen excited levels via metastable oxygen states can be reduced.