Electric field distribution in an atmospheric pressure, ns pulse discharge helium plasma jet

Temporal and spalial distributions of the electric field in an atmospheric pressure, ns pulse discharge helium plasma jet are measured by picosecond Electric Field Induced Second Harmonic (EFISH) generation. The measurements have been done in a quasi-two-dimensional I Ie plasma jet impinging on a liquid water surface, using a laser sheet or focused laser beam positioned at different heights above the surface. The discharge in the helium jet is sustained by a repetitive ns pulse voltage waveform. Absolute calibration of the electric field is provided by measuring a known electrostatic electric field distribution in the same geometry and at the same flow conditions. The vertical component of the electric field is determined by isolating the second harmonic signal with vertical polarization. The electric field is averaged over the span of the plasma jet (in the direction of the laser sheet), with the spatial resolution across the laser beam of approximately 20 µm and temporal resolution of 5 ns. The results provide essential new insight into kinetics of plasma-liquid interaction for biomedical applications, and produce data for detailed validation of high-fidelity kinetic models of atmospheric pressure plasma jets.