Densities and velocity distributions of atomic hydrogen and carbon, measured by laser-induced fluorescence with frequency tripling into the vacuum UV

Abstract

By focussing a commercial dye laser pumped with a XeCl excimer laser into phase matched Xe-A or Kr-A gas mixtures, radiation at the third-harmonic frequency has been generated in the wavelength regions: 1142–1165, 1178–1186, 1203–1224, and 1268–1290 A. VUV powers up to about 200 W have been detected by a calibrated Au-photodiode. The vacuum uv radiation has been used for the fluorescence excitation of H and C atoms produced by thermal dissociation or by a gas discharge. Absolute densities have been derived by a comparison of fluorescence intensities with intensities from Rayleigh scattering in argon. As a further application, velocity distributions of C atoms sputtered from a graphite target by 1.5 keV argon ions have been measured. These data are in good agreement with a Thompson distribution corresponding to a surface energy of 8.2 eV.