Atomic oxygen TALIF measurements in an atmospheric-pressure microwave plasma jet within situxenon calibration

Two-photon absorption laser-induced fluorescence (TALIF) is used to measure the absolute density of atomic oxygen (O) in a coaxial microwave jet in ambient air at atmospheric pressure, operated with a mixture of He and a few per cent of air. The TALIF signal is calibrated using a gas mixture containing Xe. A novel method to perform calibration in situ , at atmospheric pressure, is introduced. The branching ratios of several Xe mixtures are reported, to enable us to perform the Xe calibration without the need for a vacuum vessel. The O densities are measured spatially resolved, and as a function of admixed air to the He, and microwave power. The electron density and temperatures are measured using Thomson scattering, and the N 2 and O 2 densities are measured using Raman scattering. O densities are found to have a maximum of (4–6) × 10 22 m −3 , which indicate that O 2 is close to fully dissociated in the plasma. This is confirmed by the Raman scattering measurements. O is found to recombine mainly into species other than O 2 in the afterglow, which is suggested to consist of O 3 and oxidized components of NO.