2d spatially resolved O atom density profiles in an atmospheric pressure plasma jet: from the active plasma volume to the effluent *

Micro atmospheric pressure plasma jets (µAPPJs) are attracting high attention due to their potential to treat temperature sensitive surfaces. For these applications, reactive species are produced in the plasma. In this work two-dimensional spatially resolved absolute atomic oxygen densities are measured within a µAPPJ (COST-Jet) and in its effluent. The plasma is operated in helium with an admixture of 0.5% of oxygen at 13.56 MHz and with a power of 1 W.  Absolute atomic oxygen densities are obtained using two photon absorption laser induced fluorescence spectroscopy (TALIF). The results are reproduced by a combination of phase resolved optical emission spectroscopy (PROES) measurements and simple model calculations. Within the discharge, the atomic oxygen density builds up with a rise time of 600 µs along the gas flow and reaches a plateau of 8x10¹⁵ cm^-3. In the effluent, the density decays exponentially with a decay time of 180 µs (corresponding to a decay length of 3 mm at a gas flow of 1.0 slm). It is found that both, the species formation behavior and the maximum distance between the jet nozzle and substrates for possible oxygen treatments of surfaces can be controlled by adjusting the gas flow.