Femtosecond TALIF allows imaging atomic oxygen from interfacial plasmas in gas and liquid

Measuring the density of reactive species using direct fluorescent emission in interfacial plasmas is challenging due to the fast quenching of the excited atomic species at and below the gas-liquid interface. Exciting atomic species in a liquid using femtosecond pulses allows for fluorescent emission on time scales comparable or smaller than those allowed by the fast collision rates in a liquid. Using femtosecond two-photon absorption laser induced fluorescence (fs-TALIF) we have succeeded in demonstrating direct imaging of atomic oxygen created by an atmospheric plasma jet impinging upon water, both above and below the gas/liquid interface. We used the fs-TALIF technique for mapping the O-density in the jet above the interface with high spatial resolution. The same resonant UV two-photon excitation of O atoms followed by fluorescent emission in the liquid allowed us to determine that atomic oxygen persists for tens of microseconds in water, penetrating hundreds of micrometers into the liquid. The high spatial and temporal resolution of fs-TALIF imaging in liquids opens the door for studying reaction rates of reactive species in interfacial plasmas.