Observation of ultrafast solid-density plasma dynamics using femtosecond X-ray pulses from a free-electron laser

TL;DR

This paper demonstrates the use of femtosecond X-ray free-electron laser pulses to directly observe and characterize ultrafast plasma dynamics in solids during high-intensity laser interactions, providing new insights into electron behavior at nanometer and femtosecond scales.

Contribution

It introduces a novel experimental technique using small angle X-ray scattering with femtosecond X-ray free-electron lasers to study solid-density plasma dynamics in real-time.

Findings

Verified numerical simulations of electron density dynamics.

Observed transient grating formation due to plasma expansion.

Achieved simultaneous nanometer spatial and femtosecond temporal resolution.

Abstract

The complex physics of the interaction between short pulse high intensity lasers and solids is so far hardly accessible by experiments. As a result of missing experimental capabilities to probe the complex electron dynamics and competing instabilities, this impedes the development of compact laser-based next generation secondary radiation sources, e.g. for tumor therapy [Bulanov2002,ledingham2007], laboratory-astrophysics [Remington1999,Bulanov2015], and fusion [Tabak2014]. At present, the fundamental plasma dynamics that occur at the nanometer and femtosecond scales during the laser-solid interaction can only be elucidated by simulations. Here we show experimentally that small angle X-ray scattering of femtosecond X-ray free-electron laser pulses facilitates new capabilities for direct in-situ characterization of intense short-pulse laser plasma interaction at solid density that allows simultaneous nanometer spatial and femtosecond temporal resolution, directly verifying numerical simulations of the electron density dynamics during the short pulse high intensity laser irradiation of a solid density target. For laser-driven grating targets, we measure the solid density plasma expansion and observe the generation of a transient grating structure in front of the pre-inscribed grating, due to plasma expansion, which is an hitherto unknown effect. We expect that our results will pave the way for novel time-resolved studies, guiding the development of future laser-driven particle and photon sources from solid targets.