Experimental observation and computational modeling of radial Weibel instability in high intensity laser-plasma interactions

TL;DR

This study combines high-resolution shadowgraphy and particle-in-cell simulations to observe and model the radial Weibel instability and ionization front expansion in high-intensity laser-plasma interactions, revealing relativistic expansion and filamentation dynamics.

Contribution

It provides the first detailed experimental visualization of radial Weibel instability in laser-produced plasmas and links it to electron dynamics and magnetic field generation through simulations.

Findings

Ionization front expands at approximately 0.77c.

Filamentation persists for several picoseconds.

The Weibel instability seeds plasma heating and recombination.

Abstract

When a relativistic intensity laser interacts with the surface of a solid density target, suprathermal electron currents are subject to Weibel instability filamentation when propagating through the thermal population of the bulk target. We present time resolved shadowgraphy of radial ionization front expansion and Weibel instability filamentation within a thin, sub-micron, sheet initiated by irradiation with a short pulse, high intensity laser. High temporal (100 fs) and spatial (1 $\mu$m) resolution shadowgraphy of the interaction reveals a relativistic expansion of the ionization front within a 120 $\mu$m diameter region surrounding the laser-target interaction, corroborated by simulations to expand at $0.77c$, where $c$ is the speed of light. Filamentation within the patch persists for several picoseconds and seeds the eventual recombination and heating dynamics on the nanosecond timescale. Particle-in-cell simulations were conducted to elucidate the electron dynamics leading to the radial expansion of the critical surface. Computational results report the ionization expansion is due to field ionization of the expanding hot electron population. Filamentation within the expansion is due to the Weibel instability which is supported by the magnetic fields present.