Electron Dynamics at High-Energy Densities in Nickel from Non-linear Resonant X-ray Absorption Spectra

TL;DR

This paper investigates how intense X-ray pulses from free-electron lasers induce non-linear electron dynamics in nickel, revealing spectral changes explained by a rate model of electron populations during the pulse.

Contribution

It introduces a predictive rate model for electron dynamics in nickel under high-fluence X-ray irradiation, capturing non-linear spectral features.

Findings

Observation of non-linear spectral changes at high fluences

Development of a rate model describing electron population dynamics

Identification of key features in X-ray absorption spectra

Abstract

The pulse intensity from X-ray free-electron lasers (FELs) can create extreme excitation densities in solids, entering the regime of non-linear X-ray-matter interactions. We show L3-edge absorption spectra of metallic nickel thin films with fluences entering a regime where several X-ray photons are incident per absorption cross-section. Main features of the observed non-linear spectral changes are described with a predictive rate model for electron population dynamics during the pulse, utilizing a fixed density of states and tabulated ground-state properties.