Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 72: Symposium: Beyond Optical Wavelengths: Time-Resolved Spectroscopy of Surface Dynamics with EUV and XUV Radiation II (Invited Speakers: Wilfried Wurth, Hermann Dürr, Shik Shin)
O 72.2: Vortrag
Donnerstag, 28. Februar 2008, 14:30–14:45, HE 101
Excitation of electrons in Silicon with an ultrashort XUV free electron laser pulse: a Monte-Carlo study — •Nikita Medvedev and Baerbel Rethfeld — Technische Universitaet Kaiserslautern, 67653, Germany
The new light source FLASH at DESY in Hamburg provides ultrashort high intensity XUV pulses. We study the interaction of this new kind of irradiation with condensed matter theoretically. In this contribution we present first simulations, applying Classical Trajectory Monte Carlo simulation (CTMC) to describe the dynamics of electronic excitation and ionization within a solid silicon target, irradiated with femtosecond XUV laser pulse (25 fs, ℏω = 38 eV). The CTMC-method was extended to take into account the electronic band structure and Pauli’s principle for electrons excited into the conduction band. Secondary excitation and ionization processes were included as well. We calculate the temporal distribution of the density of exited and ionized electrons, the energy of these electrons and the energy distribution function. The influence of the band structure on the redistribution of free electrons on subpicosecond time-scale is studied. It is demonstrated that the final kinetic energy of free electrons is much less than the total energy provided by the laser pulse, because some part of energy is spended to overcome ionization potentials and is kept by holes. It was found that the total number of free electrons is significantly less than estimated by ne = ℏω / Egap. We introduce the concept of an "effective band gap", which can be applied to estimate the free electron density for collective electronic excitation with a high-intensity XUV laser pulse.