Plasma particle analysis near the surface in barrier discharges by evanescent laser spectroscopy using optical waveguide

An evanescent-wave laser absorption technique using an optical waveguide has been developed to measure the density of the metastable atoms in the vicinity of the barrier surface in a plane parallel barrier gas discharge. The optical waveguide on the surface of barrier material, LiNbO3 crystal, is produced by a proton exchange in an H2PO4 solution. A property of an optical transmission in the waveguide is checked experimentally and light with three TM-modes can propagate in the waveguide. The waveguide depth is estimated to be about 0.88 μm. The LiNbO3 with the waveguide is utilized as one dielectric of a barrier discharge and the matastable density existing in the penetration depth of evanescent-wave from the surface, 50 nm, is directly measured from the absorption signal. The surface density is measured at various gas pressures of Ar and frequencies of pulsed voltage applied from a power supply. The surface density is also compared with the density in the bulk plasma.