Observation of Self-Sustaining Relativistic Ionization Wave Launched by Sheath Field

TL;DR

This paper reports the experimental observation and simulation of a relativistic ionization wave driven by sheath fields in plasma filaments created by high-intensity laser pulses, revealing a self-sustaining propagation mechanism.

Contribution

It provides the first experimental evidence and simulation support for a relativistic ionization wave launched by sheath fields in laser-created plasma filaments, highlighting a novel self-sustaining process.

Findings

Ionization wave propagates at 0.2-0.5 c for about 2 ps

Wave doubles the initial filament radius

Sheath field traps high-energy electrons to sustain the wave

Abstract

We present experimental evidence supported by simulations of a relativistic ionization wave launched into surrounding gas by the sheath field of a plasma filament with high energy electrons. Such filament is created by irradiating a clustering gas jet with a short pulse laser ($\sim$115 fs) at a peak intensity of $5 \times 10^{17}$ W/cm$^2$. We observe an ionization wave propagating radially through the gas for about 2 ps at 0.2-0.5 $c$ after the laser has passed, doubling the initial radius of the filament. The gas is ionized by the sheath field, while the longevity of the wave is explained by a moving field structure that traps the high energy electrons near the boundary, maintaining a strong sheath field despite the significant expansion of the plasma.