A Novel Sub-1 V/cm, Phase-Sensitive E-FISH Diagnostic System for Space-Time Resolved Electric Field Measurements in Electrical Discharges*

Sub-nanosecond and spatially-resolved measurements of electric field (E-field) magnitudes are crucial under high-pressure conditions due to the rapid transient dynamics occurring when plasmas are generated by excitation voltages with fast rise times. Coherent pulsed laser diagnostic techniques, such as Electric Field-Induced Second Harmonic Generation (E-FISH), provide high spatial-temporal resolution but are limited by a quadratic dependence on E-field strength, restricting their effectiveness at low E-field strengths. We report a significant improvement in the detection limit of the E-FISH diagnostic method for E-field measurements at atmospheric pressure, achieving an enhancement of 2-3 orders of magnitude. By integrating heterodyne detection with a sensitive detector and accounting for phase-matching effects, we have reduced the detection limit to approximately 1 V/cm at atmospheric pressure. Additionally, the technique demonstrates sensitivity to the polarity of the electric field when using AC voltage waveforms, while maintaining sub-nanosecond temporal resolution. This advanced system, when utilized to take high space-time resolved measurements of volumetric ionization waves and streamer discharges, is expected to provide novel insights into the dynamic nature of these discharges.