Absolute Atomic Oxygen Density Measurements by Two-Photon Laser-induced Fluorescence (TALIF) in the Effluent of an Atmospheric Pressure Plasma Jet

A 13.56 MHz RF-excited plasma jet$^{1}$ is diagnosed in this work. The jet operates at ambient conditions. It generates a homogeneous plasma in helium or argon$^{2}$ with admixtures ( $\sim $ 1 {\%}) of molecular gases, here oxygen. The temperature of the effluent is well below 100\r{ }C. The jet has been set up in a planar and a concentric version; both were compared by means of TALIF-measurements. Absolute atomic oxygen density profiles have been measured in the effluent of the plasma jet. The atomic oxygen density close to the nozzle amounts to 10$^{16}$ cm$^{-3}$. Even at several centimeters from the nozzle there still is 1{\%} of the initial oxygen density. Emission spectroscopy down to 110 nm has been carried out as a function of distance from the exit nozzle with the effluent hitting an MgF$_{2}$ window in front of the slit of a vacuum UV monochromator. These spectra exhibit strong emission lines e.g. of oxygen at 130 nm, even at a distance of several centimeters from the nozzle. This work was supported by the ``Ministerium f\"{u}r Wissenschaft und Forschung NRW'' \newline $^{1}$J. Y. Jeong, S. E. Babayan, V. J. Tu, J. Park, R. F. Hicks, and G. S. Selwyn, PSST \textbf{7}, 282 (1998). \newline $^{2}$S. Wang, V. Schulz-von der Gathen, H.F. D\"{o}bele, Appl. Phys. Lett. \textbf{83}, 3272 (2003)