Electric Field Comparison Between RF and ns-Pulsed Plasmas at the Plasma-Liquid Interface Using Electric Field-Induced Second Harmonic Generation (EFISH)

This work details measurements of the electrical field for a nanosecond-pulsed plasma and a radio-frequency (RF) -powered plasma using the electric field-induced second harmonic generation (EFISH) technique. The plasma is generated by flowing helium through a high voltage, hollow, tubular electrode onto saltwater which is contained within a copper-tape lined Petri dish placed on top of a ground plate. The electrical field is measured by a femtosecond laser pulse polarized in the axial direction, the direction pointing from the HV electrode to liquid surface. The calibrations of EFISH was performed with a known plate-to-plate electric field and needle-to-plate configuration with the same flow rate. The measured electrical fields, both spatially and temporally resolved, of the two plasmas are then compared to determine the impact of power schemes on the field distribution and development. Understanding this power dependence of the electric field is important to determine the plasma physics and chemistry for a variety of applications.