Gas phase air and water concentrations near the interface in plasma–water interaction

The quenching process of excited states in the plasma highly relies on long-lived quenching agents such as air and H2O. With the help of the total quenching rates of the excited state NO(A2Σ+), accessed by the decay of laser-induced fluorescence signals, we present a precise measurement of the gas-phase air and H2O concentrations in the plume of a plasma jet. The spatial distributions of air fraction and water vapor concentration are visualized for a freely expanding plasma jet in ambient air, and also for the jet with a glass target and a water target. The air fraction and water vapor density are not uniform in space, with the maximum values located at the bottom corner near the plasma–target interface.