Dresden 2009 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 50: Ultra fast phenomena
HL 50.6: Talk
Friday, March 27, 2009, 11:45–12:00, BEY 118
Electronic dynamics of semiconductors irradiated with an ultrashort VUV laser pulse — •Nikita Medvedev and Baerbel Rethfeld — Technical University of Kaiserslautern, Erwin Schroedinger Str. 46, 67663 Kaiserslautern, Germany
We investigate theoretically the interaction of an ultrashort high-intensity VUV laser pulses produced in a new light source FLASH (at DESY in Hamburg) with semiconductors. In our contribution we present numerical simulations of excitations of electronic subsystem within a solid silicon target, irradiated with femtosecond laser pulse (total duration of 25 fs, and photon energy ℏω = 38 eV). The Monte Carlo method (ATMC) was extended in order 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 and simulated event by event as well.
In the presented work, the temporal distribution of the density of free electrons, the energy of these excited electrons and their energy distribution function were calculated. It is demonstrated that due to the fact that part of the energy is spent to overcome ionization potentials, the final kinetic energy of free electrons at the moment of 25 fs is much less than the total energy provided by the laser pulse. 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 VUV laser pulse as an expression: ne = ℏω / Egapeff. Effective band gap depends on properties of material as well as on laser pulse.