Characterization of an N2 flowing microwave post-discharge by OES spectroscopy and determination of absolute ground-state nitrogen atom densities by TALIF

A flowing microwave post-discharge source sustained at 2.45 GHz in pure nitrogen has been investigated by optical emission spectroscopy (OES) and two-photon absorption laser-induced fluorescence (TALIF) spectroscopy. Variations of the optical emission along the post-discharge (near, pink and late afterglow) have been studied and the gas temperature has been determined. TALIF spectroscopy has been used in the late afterglow to determine the absolute ground-state nitrogen atomic densities using krypton as a reference gas. Measurements show that the microwave flowing post-discharge is an efficient source of N (S-4) atoms in late afterglow. In our experimental conditions, the maximum N (S-4) density is about 2.2 x 10(15) cm(-3) for a pressure of 22 Torr, at 300 K. The decay of N (S-4) density as a function of the time spent in the quartz tube has been modelled and a wall recombination probability. of (2.1 +/- 0.3) x 10(-4) is obtained.