Absolute atomic oxygen ground state densities in a radio-frequency driven atmospheric pressure plasma jet, operated in a helium-oxygen mixture, are determined using diagnostic based modeling. One-dimensional numerical simulations of the electron dynamics are combined with time integrated optical emission spectroscopy. The population dynamics of the upper O 3p~3P (λ= 844 ran) atomic oxygen state is governed by direct electron-impact excitation, dissociative excitation, radiation losses, and collisional-induced quenching. Absolute values for atomic oxygen densities are obtained through comparison with the upper Ar 2p_1 (λ= 750.4 nm) state. Results for spatial profiles and power variations are presented and show excellent quantitative agreement with independent two-photon absorption laser-induced fluorescence measurements.
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