Electronic and atomic kinetics in solids irradiated with free-electron lasers or swift-heavy ions

TL;DR

This review compares the transient electronic and atomic processes in solids caused by femtosecond X-ray free-electron laser pulses and swift-heavy ion irradiation, highlighting similarities, differences, and underlying mechanisms.

Contribution

It provides a comparative analysis of electronic and atomic relaxation kinetics under FEL and SHI irradiation, emphasizing the effects of geometry and initial excitation.

Findings

Electronic and atomic relaxation share common origins in both irradiation types.

Differences in kinetics are due to geometrical effects and initial irradiation conditions.

Models of electron transport and electron-lattice coupling are discussed with their limitations.

Abstract

In this brief review we discuss the transient processes in solids under irradiation with femtosecond X-ray free-electron-laser (FEL) pulses and swift-heavy ions (SHI). Both kinds of irradiation produce highly excited electrons in a target on extremely short timescales. Transfer of the excess electronic energy into the lattice may lead to observable target modifications such as phase transitions and damage formation. Transient kinetics of material excitation and relaxation under FEL or SHI irradiation are comparatively discussed. The same origin for the electronic and atomic relaxation in both cases is demonstrated. Differences in these kinetics introduced by the geometrical effects ({\mu}m-size of a laser spot vs nm-size of an ion track) and initial irradiation (photoabsorption vs an ion impact) are analyzed. The basic mechanisms of electron transport and electron-lattice coupling are addressed. Appropriate models and their limitations are presented. Possibilities of thermal and nonthermal melting of materials under FEL and SHI irradiation are discussed.