Measurement of dynamics of plasma excited species on dielectric surface using waveguide type optical near field

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In recent discharge applications, an interaction between excited species produced in plasma and dielectric surface is fundamentally important. A new technique using an waveguide type optical near field laser spectroscopy is developed to quantitatively observe the excited species on the dielectric surface in plasma.1.An optical waveguide on LiNbO_3 crystal was produced by ion-exchanging method. Ion-exchange was performed with H_3PO_4 liquid in high temperature and an annealing in oxygen gas made it possible to reduce a transmission loss. From the comparison with theoretical analysis of waveguide, the optimum waveguide depth was determined to be 1.8 μm and the laser transmission in TM0 mode was suit for this experiment2.Using LiNbO_3 with waveguide, a parallel plate barrier discharge device was constructed in a vacuum chamber. The discharge was produced with a pure Ar gas. Laser was incident to the waveguide from a coupling prizm and the optical near field appeared on the waveguide interacted with Ar metastable atoms in the vicinity of surface. After transmitting in the waveguide, the absorbed laser was detected. As a result of improvement of the optical system, the absorption signal due to metastables was obtained with a high S/N.3.Ar metastable density on the dielectric surface was measured from the absorption signal as a function of Ar gas pressure up to 50 Torr and it was clear that the dependence on pressure was much different from the dependence of metastables in bulk plasma. The flux of metastables on the surface was estimated.4.A new phenomenon such that the transmitted laser intensity considerably decreased in exponentially just after the discharge started was found experimentally. This phenomenon should be analyzed. This experimental technique must be mixed with a cross-beam type spectroscopic method in order to observe a dynamic behavior of excited species on the surface.