Analyses of spatiotemporal dynamic behavior of microplasmas near a dielectric surface in microplasma using an optical near field

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It is necessary to gain knowledge of the dynamics of excited species and accumulated charges near or on the dielectric surface in order to discuss the plasma characteristics in a barrier discharge and to consider efficient plasma applications. We developed techniques such as laser-induced evanescent-mode fluorescence (LIEF), cross-beam type LIEF and waveguide type laser absorption to quantitatively study a surface dynamics such as surface reflection of the excited metastable atoms in a microplasma for a plane parallel or a coplanar electrode type barrier discharge.We also developed an optical technique using an electro-optic crystal as a dielectric barrier in order to observe dynamics of accumulated surface charges. We found that the dynamics of surface charges is strongly dependent on gas pressures and a breakdown voltage is mainly determined by a surface charge density. From these measurements, the relation between true breakdown voltage and plasma homogeneity in a micro-gap atmospheric barrier discharge is discussed using a Streamer theory. It is clarified that the surface charges are modulated by an external irradiation of light. This makes possible to control a barrier discharge using an external light irradiation. Using these results obtained, the discharge mechanism of a plasma display panel, characteristics of a two-dimensional micro-array type VUV light source working at pressures higher than one atmosphere and the property of microplasma jet are investigated.We made experiments for disinfection of Bacillus spore forming bacteria and pathogenic species using atmospheric pressure plasma in a coplanar type barrier discharge, a pulse-modulated high frequency atmospheric discharge and a micro-gap discharge. The reduction of the heating, thermal effect and significantly strong antibacterial effect are realized.