Few-femtosecond resolved imaging of laser-driven nanoplasma expansion

TL;DR

This paper demonstrates that x-ray coherent diffractive imaging can quantitatively capture nanoplasma expansion dynamics in real-time, revealing detailed shell-wise evolution and startup delays with femtosecond resolution.

Contribution

It introduces a novel application of time-resolved diffractive imaging to observe laser-driven nanoplasma expansion with unprecedented temporal and spatial resolution.

Findings

Resolved nearly self-similar plasma profile evolution

Exposed shell-wise expansion dynamics including startup delay

Measured rarefaction front velocity

Abstract

The free expansion of a planar plasma surface is a fundamental non-equilibrium process relevant for various fields but as-yet experimentally still difficult to capture. The significance of the associated spatiotemporal plasma motion ranges from astrophysics and controlled fusion to laser machining, surface high-harmonic generation, plasma mirrors, and laser-particle acceleration. Here, we show that x-ray coherent diffractive imaging can surpass existing approaches and enables the quantitative real-time analysis of the sudden free expansion of nanoplasmas. For laser-ionized SiO$_2$ nanospheres, we resolve the formation of the emerging nearly self-similar plasma profile evolution and expose the so far inaccessible shell-wise expansion dynamics including the associated startup delay and rarefaction front velocity. Our results establish time-resolved diffractive imaging as an accurate quantitative diagnostic platform for tracing and characterizing plasma expansion and indicate the possibility to resolve various laser-driven processes including shock formation and wave-breaking phenomena with unprecedented resolution.