E-FISH Technique Measured Electric Field of RF Atmospheric Pressure Plasma Jet in Helium-Nitrogen Mixture*

Radio Frequency Atmospheric Pressure Plasma Jets (RF-APPJ) are well known and thoroughly studied. However, accurate experimental measurements of their electric fields are lacking. Optical Emission Spectroscopy (OES) techniques are complicated due to the complex helium-nitrogen discharge chemistry and probes are inapplicable because of miniature device sizes. Moreover, low absolute values of E-fields in RF-APPJ make the E-field measurements challenging. This work presents, to the authors’ best knowledge, the first measurements of the E-field in a helium-nitrogen RF-APPJ performed using E-Field Second Harmonic generation (E-FISH), a non-resonant spatially resolved laser technique that utilizes the ability of a medium to generate a second harmonic signal in presence of an external E-field. Contrary to low pressure Capacitively Coupled Plasmas (CCP), the phase shift between the applied voltage and the E-field significantly deviates from -π/2. By applying a simple RC equivalent model, the phase shift allows an estimate of the mean electron density. Electron density and E-field amplitude combined provide a calibration of the absolute excitation rate. Future plans include 1D measurements of the E-field at various positions of the inter-electrode gap alongside with Particle-in-Cell / Monte Carlo collisions (PIC/MCC) simulations for fundamental insights into the discharge.