Diagnostics of atoms by laser spectroscopic methods in plasmas and plasma-wall interaction studies (vacuum ultraviolet and two-photon techniques)

We describe in this paper the measurement of light atom concentrations in plasmas and their detection in plasma-wall interaction experiments. VUV radiation or multiphoton techniques are required due to the large energy differences between the ground state and the excited states. We discuss briefly commonly applied schemes of nonlinear optics to generate narrow-bandwidth tunable VUV radiation with particular emphasis on high-order stimulated anti-Stokes Raman scattering in hydrogen gas. Applications of absorption and laser-induced fluorescence spectroscopy both to discharges and experiments with ion beams on targets are described. The discussion of multiphoton techniques focuses on the detection of sputtered atoms by resonantly enhanced multiphoton ionization (REMPI) and the detection of O and H in radiofrequency excited plasma reactors. Methods of absolute calibration and limitations by collisional effects are considered in this context. Examples of the detection of atomic hydrogen by light mixing are outlined in the conclusion.