Density and temperature of N atoms in the afterglow of a microwave discharge measured by a two-photon laser-induced fluorescence technique

Abstract

Both the axial density and temperature profiles of ground-state nitrogen atoms have been measured in a microwave discharge and its afterglow in the presence of the so-called short-lived afterglow by means of two-photon absorption laser-induced fluorescence (TALIF). The temperature is obtained from the Doppler broadening of the spectral profile, after deconvolution with the laser profile. The N atom temperature decreases from about 1400 K in the end of the discharge zone to about 300 K in the downstream part of the afterglow. The sharp temperature decrease immediately behind the discharge zone can reasonably be explained by heat transfer to the flow tube wall. The absolute N atom density is obtained by calibrating the fluorescence yield with a TALIF signal from krypton atoms. The N density increases from 1.5*10/sup 21/ m/sup -3/ in the discharge zone to about 3.5*10/sup 21/ m/sup -3/ in the late afterglow. However, the N atom flux is conserved along the flow tube, indicating negligible consumption or production of N atoms in the short-lived afterglow