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

Both the axial density and temperature profiles of ground-state nitrogen at oms have been measured in a microwave discharge and its afterglow in the pr esence of the so-called short-lived afterglow by means of two-photon absorp tion laser-induced fluorescence (TALIF). The temperature is obtained from t he Doppler broadening of the spectral profile, after deconvolution with the laser profile. The N atom temperature decreases from about 1400 K in the e nd of the discharge zone to about 300 K in the downstream part of the after glow. The sharp temperature decrease immediately behind the discharge zone can reasonably be explained by heat transfer to the how tube wall. The abso lute N atom density is obtained by calibrating the fluorescence yield with a TALIF signal from krypton atoms. The N density increases from 1.5 x 10(21 ) m(-3) in the discharge zone to about 3.5 x 10(21) m(-3) in the late after glow. However, the N atom flux is conserved along the flow tube, indicating negligible consumption or production of N atoms in the short-lived aftergl ow.