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A: Fachverband Atomphysik

A 38: Atomic Clusters IV

A 38.1: Vortrag

Freitag, 6. März 2009, 14:00–14:15, VMP 6 HS-C

Collision frequency of electrons in laser excited expanding small clusters — •Thomas Raitza, Heidi Reinholz, and Gerd Röpke — Universität Rostock

One of the fundamental quantities in the physics of strongly coupled Coulomb systems is the dynamical collision frequency. Collisions are of relevance for emission, absorption, reflection and scattering of light. Analytical as well as MD simulation techniques have been applied to evaluate the dynamical collision frequency for homogeneous systems, with special application to optical properties. Recently, clusters at nearly solid densities are more accessible to experimental investigations using laser intensities of 10¹³ − 10¹⁶ W cm⁻². Here, we present theoretical results for finite Coulomb systems. In particular, we are interested in the cluster size dependence of the collisional damping rates in comparison to bulk systems.

Properties of laser excited small metallic clusters are calculated using a classical MD simulations code. Results for the electron phase space distribution are analyzed, comparing the simulated profiles with predictions from equilibrium statistical physics. We are interested in time dependent density and temperature profiles as well as optical properties. The question of local thermodynamic equilibrium (LTE) is addressed, and size effects are considered. For this, a restricted MD simulation scheme has been developed, where the ion positions are frozen at given times, and the electrons are treated as an equilibrated subsystem. Collective modes of the excited electron system have been investigated in order to deduct the dynamical collision frequency.