Darmstadt 2008 – scientific programme

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A: Fachverband Atomphysik

A 1: Attosecond electron dynamics

A 1.4: Talk

Monday, March 10, 2008, 15:00–15:15, 3C

Monte-Carlo study of electronic dynamics in semiconductors with an ultrashort XUV-laser pulse — •Nikita Medvedev and Baerbel Rethfeld — Technische Universitaet Kaiserslautern, Kaiserslautern, Germany

We study theoretically the interaction of condensed matter with a new kind of ultrashort high-intensity XUV laser pulses (new light source FLASH at DESY in Hamburg). In our contribution we present first numerical simulations of the excitation and ionization of the electronic subsystem within a solid silicon target, irradiated with femtosecond laser pulse (25 fs, ℏω = 38 eV). The Classical Trajectory Monte Carlo method was extended in order to take into account the electronic band structure for electrons excited into the conduction band. Secondary excitation and ionization processes were included and simulated event by event as well. The influence of the band structure on the redistribution of free electrons on subpicosecond time-scale is analyzed. In the presented work the temporal distribution of the density, the energy of these electrons, and their energy distribution function were calculated. It is demonstrated that due to the fact that part of the energy is spended to overcome ionization potentials and is kept by holes, the final kinetic energy of free electrons is much less than the total energy provided by the laser pulse. The final total number of electrons excited by single photon is significantly less than estimated by simplest expression n_e = ℏω / E_gap. We introduce the concept of an "effective band gap" for collective electronic excitation, which can be applied to estimate the free electron density after high-intensity XUV laser pulse.