Resonantly-Enhanced E-FISH for Picosecond Time-resolved Electric Field Measurements in Low-Pressure Electrical Discharges.

The Electric Field Induced Second Harmonic (E-FISH) generation technique offers unique capabilities for space-time resolved electric field measurements in diverse high-pressure electrical discharges, from pin-to-pin configurations to dielectric barrier discharges powered by either nanosecond DC pulsed or radiofrequency electrical excitation waveforms. This contribution details a pivotal expansion of this well-established diagnostic within the low-temperature plasma community: its inaugural application to electrical discharges sustained at low pressures (below 1 Torr). Our approach re-evaluates the role of gas properties, specifically harnessing the significant wavelength dependence of the third-order hyperpolarizability, a factor previously neglected by the community. By leveraging strong enhancements achieved at electronic resonances of alkali vapor gases, we present experimental results obtained in argon with minimal addition of sodium vapor enabling enhanced sensitivity under low-pressure conditions. This work paves the way for new insights into low-pressure plasma physics, and we will discuss both the pathways for further sensitivity enhancements and the inherent limitations related to phase-matching.