Measurement of atomic oxygen densities using TALIF in dielectric barrier discharge: Insights into the effluent of a micro cavity plasma array*

Dielectric barrier discharges, particularly micro cavity plasma arrays, show great potential for plasma-catalytic research due to their ability to ignite a plasma in direct contact with a catalytic surface, allowing the observation of plasma-surface interactions. A key to their application is the production of reactive species, such as atomic oxygen, within the cavities. These species can interact with both the surface (e.g. activation or cleaning) and the gas being treated (e.g. oxidation). Given the central role of O atoms in plasma catalysis and its use as a model for more complex species, this work determines absolute densities in the effluent of the cavities using two-photon absorption laser-induced fluorescence spectroscopy (TALIF). The reactor operates with a He/O_2 mixture at a flow rate of 1 slm at atmospheric pressure. Densities up to 10^16 cm^-3 are measured near the surface. O_2 admixture variations show a density maximum at 0.4%. Spatially resolved measurements reveal that O density decreases exponentially from the surface but remains measurable about 1 mm above it, indicating significant application potential. Time-resolved measurements show that the density in the effluent is not time-dependent on the driving frequency (15 kHz). The build-up and decay times of the density when the discharge is switched on and off are around 1 ms. These findings allow further optimization of the reactor for plasma-catalytic applications and verify previous OES measurements within the cavities.