TALIF Measurements of Spatial Distribution of Atomic Oxygen in Sub-Atmospheric Pressure Oxygen Discharges

Atmospheric pressure plasma is expected to be applied in various fields with its abundant radical production. However, radicals produced in atmospheric pressure plasma have a short lifetime. Sub-atmospheric pressure plasma, in which the pressure is slightly reduced from atmospheric pressure, is considered as an effective tool of extending the lifetime of radicals while maintaining the radical production yield. In this study, the density of atomic oxygen was measured by TALIF produced in a sub-atmospheric pressure pure oxygen barrier discharge using pin-to-sphere electrodes and two power supplies with 300 ns or 35 ns voltage pulse width. The results show that the amount of atomic oxygen increased significantly near the cathode surface with dielectric in discharges using a long-pulse power supply. In contrast, the amount of atomic oxygen was almost independent of position in discharges using a short-pulse power supply. The lifetime of the atomic oxygen increased with decreasing pressure. One possible reason for the increased production of O atom near the dielectric in long-pulsed discharges is that the discharge area may have expanded due to surface discharges along the dielectric.