Spark-Induced Shockwave Dynamics Revealed via Nonresonant Four-Wave Mixing

TL;DR

This paper introduces a novel optical technique using nonresonant four-wave mixing to experimentally observe and analyze shockwave dynamics generated by spark discharges, providing insights into transient flow behaviors.

Contribution

It demonstrates the first application of nonresonant four-wave mixing for real-time detection of shockwave-induced density perturbations and flow velocities in spark discharges.

Findings

Detection of local density perturbations via single-shot coherent Rayleigh-Brillouin scattering.

Observation of shock-induced flow velocities as spectral features.

Validation of measurements against one-dimensional flow simulations.

Abstract

We report on the experimental detection of shockwave dynamics produced in a spark discharge, using a nonresonant four-wave mixing optical technique. In particular, we observe the spark-induced local density perturbation across a millimeter-range probe volume, centered on the discharge, via single-shot coherent Rayleigh-Brillouin scattering. We detect the emergence of shock-induced flow velocities, which appear as distinct features in the spectrum, and monitor their dynamic evolution from a few hundred nanoseconds to microseconds after the spark. Finally, we benchmark our measurements against simulations based on a one-dimensional compressible flow model. Our results pave the way for quantitative measurements of highly non-uniform transient flows in challenging environments featuring non-equilibrium gas kinetics.