Nanoscale femtosecond imaging of transient hot solid density plasmas with elemental and charge state sensitivity using resonant coherent diffraction

TL;DR

This paper proposes a novel resonant coherent X-ray diffraction method using XFELs to image transient hot plasmas at nanoscale resolution, enabling detailed observation of plasma dynamics and ion distributions.

Contribution

It introduces the use of resonant X-ray scattering to distinguish ionic signals from free electrons in laser-excited plasmas, enhancing spatial and temporal resolution.

Findings

Resonant scattering significantly increases ionic signal detectability.

Method allows measurement of ion distributions and plasma temperature.

High-resolution imaging of plasma dynamics is achievable.

Abstract

Here we propose to exploit the low energy bandwidth, small wavelength and penetration power of ultrashort pulses from XFELs for resonant Small Angle Scattering (SAXS) on plasma structures in laser excited plasmas. Small angle scattering allows to detect nanoscale density fluctuations in forward scattering direction. Typically, the SAXS signal from laser excited plasmas is expected to be dominated by the free electron distribution. We propose that the ionic scattering signal becomes visible when the X-ray energy is in resonance with an electron transition between two bound states (Resonant coherent X-ray diffraction, RCXD). In this case the scattering cross-section dramatically increases so that the signal of X-ray scattering from ions silhouettes against the free electron scattering background which allows to measure the opacity and derived quantities with high spatial and temporal resolution, being fundamentally limited only by the X-ray wavelength and timing. Deriving quantities such as ion spatial distribution, charge state distribution and plasma temperature with such high spatial and temporal resolution will make a vast number of processes in shortpulse laser-solid interaction accessible for direct experimental observation e.g. hole-boring and shock propagation, filamentation and instability dynamics, electron transport, heating and ultrafast ionization dynamics.