Nanosecond second harmonic generation for electric field measurements with temporal resolution shorter than laser pulse duration

Electric field induced second harmonic (EFISH) generation using a ns pulse duration laser has been employed for time-resolved measurements of the axial and transverse electric field in a pin-to-pin ns pulse discharge in ambient air, at atmospheric pressure and at 2 bar. The results demonstrate that the time-varying electric field can be measured accurately over the duration of the laser pulse 15-20 ns long, with the temporal resolution (potentially sub-ns) limited by the response time of the detector. Each data set provides time-accurate electric field over a period of up to 10 ns. Time-resolved electric fields over longer time periods are measured by adjusting the laser Q-switch delay, and using the composite data obtained by overlapping the individual data sets. Absolute calibration of the electric field is obtained from the comparison of the experimental data with the Laplacian field distribution in the discharge gap before breakdown, taking into account the residual charge accumulation on the surface of the dielectric encapsulating the grounded pin electrode. The results demonstrate the feasibility of ns EFISH measurements in high-pressure transient plasmas, using widely available ns pulse duration Nd:YAG lasers.