H-ATOM PLASMA DIAGNOSTICS - A SENSITIVE PROBE OF TEMPERATURE AND PURITY

Two-photon absorption laser-induced fluorescence (TALIF) has proven to be a convenient diagnostic for reactive light atoms in plasmas. We have carried out a series of TALIF experiments and report the first temperature measurements of ground state H atoms in an rf discharge. With reasonable care, measurements of the H atom linewidths, broadened by the Doppler effect, provide detailed information about the translational energy, i.e., temperature of the atoms. It is found that in pure H-2 plasma, the H atom temperature is slightly elevated with respect to ambient. In plasmas contaminated with the other H-containing molecules, Doppler-broadened linewidths corresponding to H atom temperatures in excess of 7000 K have been observed. The mechanisms leading to such high apparent temperatures are discussed.