Electron Kinetics in Femtosecond X-Ray Irradiated SiO2.
Résumé
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.