Electron Kinetics in Femtosecond X‐Ray Irradiated SiO₂

Abstract

A theoretical study of the ultrafast electron kinetics in solid SiO2, irradiated with a femtosecond X‐ray laser pulse, is presented. A Monte Carlo code for event‐by‐event simulations of individual particles is applied to model the electron kinetics within the irradiated SiO2 bulk. The simulation includes photoionization, elastic and inelastic scatterings of electrons, Auger decays of core holes, and electron‐hole recombination via exciton self‐trapping mechanism. Transient electron density is followed, at different photon energies and pulse durations. The change of the optical properties (reflectance, transmittance) of the material is estimated with the help of the Drude model. The analysis of the results allows us to conclude that within the X‐ray excited dielectric, the holes in the valence band give the predominant contribution to the transient changes of optical properties within the material. The increase rate of the free electron density is limited by the duration of secondary electron cascading. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nonthermal graphitization of diamond induced by a femtosecond x-ray laser pulse

“…33 Therefore, the higher the initial energy of the photoelectron is, the more collisions the photoelectron performs until it loses its energy below E cut . 65 Figure 3 shows the fraction of high-energy electrons (top panel) and of K-shell holes (bottom panel) as functions of time for different photon energies. For all cases the same laser-pulse shape was used: a Gaussian temporal envelope with 10-fs FWHM, delivering the absorbed dose of 0.85 eV per atom.…”

Single-shot pulse duration monitor for extreme ultraviolet and X-ray free-electron lasers

“…The irradiation of dielectrics with ultrashort XUV and X-ray laser pulses causes photoionization of electrons from bound states (deep shells and valence band) to high-energy states of the conduction band, producing energetic free electrons. A dedicated Monte-Carlo simulation tool [33][34][35][36][37] was applied to study the relaxation of the photoexcited electronic subsystem within a solid SiO 2 target irradiated with an 80-fs Gaussian XUV pulse. Typical simulation times were of the order of a few hundreds of femtoseconds.…”

“…With increasing photon energy, the contribution of secondary processes such as impact ionization and Auger processes becomes dominant and these cascades themselves last longer. Owing to the longer electron rise time, the resolution is reduced to the few-10-fs scale 37 . In Fig.…”

“…For this purpose, the temporal resolution can be enhanced to the fewfemtosecond regime by using sub-10-fs probe pulses and diffraction-limited imaging. For X-ray pulses with photon energies higher than 1 keV, the resolution is limited to the few-10-fs scale because of the longer lasting secondary electron cascades 37 . The method can operate from the XUV to X-ray wavelengths and over a large range of pulse durations as long as the absorption is linear and the duration of the X-ray pulse is longer than the secondary electron cascading.…”

Principles of femtosecond X-ray/optical cross-correlation with X-ray induced transient optical reflectivity in solids

“…The deposited energy of the X-ray pump pulse is thus converted at early timescales into low-energy electron-hole pairs across the band gap. 12 Second, energy is transferred from the electronic to the phonon system through electron-phonon coupling. The heat capacities of electrons and the lattice determine the equilibrated temperature which is reached within picoseconds after the excitation in this two temperature model.…”