On OH Density of an Atmospheric Pressure Plasma Jet by Laser-Induced Fluorescence

For room-temperature atmospheric pressure plasma jets (RT-APPJs), because of the gas flow, the OH density at a given position is different from the case without the gas flow. In this paper, an OH density decay model, which includes the main loss processes of OH and gas flow effect, is present. Based on the model, the simulation results have a very good agreement with the OH decay behavior measured by laser-induced fluorescence. The absolute OH density of the RT-APPJ is obtained when the best fit is achieved, which is about 2.4 × 10¹³ cm^-3 at 5 mm away from the plasma jet nozzle and 1 μs after the discharge. In addition, to control the OH density, the effect of voltage polarity, applied voltage magnitude, pulse frequency, pulsewidth on the OH density is also investigated and discussed.