Absolute atomic oxygen density distributions in the effluent of a microscale atmospheric pressure plasma jet

The coplanar microscale atmospheric pressure plasma jet (mu-APPJ) is a capacitively coupled radio frequency discharge (13.56 MHz, similar to 15W rf power) designed for optimized optical diagnostic access. It is operated in a homogeneous glow mode with a noble gas flow (1.4 slm He) containing a small admixture of molecular oxygen (similar to 0.5%). Ground state atomic oxygen densities in the effluent up to 2 x 10(14) cm(-3) are measured by two-photon absorption laser-induced fluorescence spectroscopy (TALIF) providing space resolved density maps. The quantitative calibration of the TALIF setup is performed by comparative measurements with xenon. A maximum of the atomic oxygen density is observed for 0.6% molecular oxygen admixture. Furthermore, an increase in the rf power up to about 15W (depending on gas flow and mixture) leads to an increase in the effluent's atomic oxygen density, then reaching a constant level for higher powers.