Picosecond interferometry and analysis of pressure fields around nanosecond microdischarge filaments that develop in deionized water

Abstract

This study investigated pressure fields that develop around nanosecond discharges produced in deionised water by fast rise-time positive high-voltage pulses (+100 kV, duration 10 ns) on a point electrode by means of laser interferometry with high spatial resolution (0.75 μm). The concept of the Mach–Zehnder interferometer was employed using Nd:YAG laser (532 nm, 30 ps). Changes in the liquid refractive index produced a shift in the fringes in interference patterns projected by the interferometer. High spatial resolution combined with the ultrafast laser source allowed the acquisition of interferometric images at any phase of the discharge evolution. Consequently, unique results were obtained that characterised pressure fields that develop due to the propagation of a single discharge filament. The peak pressure of 500 MPa was estimated at the shock front with a radius of 2 μm; the generating filament was invisible at this early stage. The shockwave amplitudes were probably voltage independent.