Plasma surface dynamics and smoothing in the relativistic few-cycle regime

TL;DR

This paper presents a theoretical explanation for plasma surface smoothing observed in femtosecond relativistic laser interactions, highlighting the role of coherent electron motion in stabilizing the plasma surface and its implications for advanced applications.

Contribution

It introduces a novel theoretical model explaining plasma surface smoothing in the few-cycle relativistic regime, differing from longer pulse interactions.

Findings

Surface dynamics are dominated by coherent electron motion.

Plasma surface smoothing occurs on femtosecond timescales.

Unique stabilization effects influence high-intensity laser applications.

Abstract

In laser-plasma interactions it is widely accepted that a non-uniform interaction surface will invariably seed hydrodynamic instabilities and a growth in the amplitude of the initial modulation. Recent experimental results [Dromey, Nat. Phys. 2009] have demonstrated that there must be target smoothing in femtosecond timescale relativistic interactions, contrary to prevailing expectation. In this paper we develop a theoretical description of the physical process that underlies this novel phenomena. We show that the surface dynamics in the few-cycle relativistic regime is dominated by the coherent electron motion resulting in a smoothing of the electron surface. This stabilization of plasma surfaces is unique in laser-plasma interactions and demonstrates that dynamics in the few-cycle regime differ fundamentally from the longer pulse regimes. This has important consequences for applications such as radiation pressure acceleration of protons and ions and harmonic generation from relativistically oscillating surfaces.