Berlin 2014 – scientific programme

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MO: Fachverband Molekülphysik

MO 4: Theory 1: Molecular Dynamics

MO 4.1: Invited Talk

Monday, March 17, 2014, 14:00–14:30, BEBEL SR144

Ultracold Rydberg plasma formation in intense laser-cluster interactions: resolving the mystery of highly charged ions — •Thomas Fennel — Institute of Physics, University of Rostock, Rostock, Germany

Many strong-field cluster experiments have demonstrated the emission of atomic ions in extreme ionization stages of q≥20, e.g. in Ref [1]. This observation is commonly interpreted as a proof for ultraefficient light absorption in laser-induced nanoplasmas, e.g. through transient resonant plasmonic heating in near-infrared pulses. However, it can be shown that electron removal from the cluster during the laser pulse - this outer ionization is what one would intuitively require for ionization - is insufficient to explain observed average charge states [2]. Striking evidence for this apparent contradiction is given by recent FEL experiments on large Xe clusters [3]. Via molecular dynamics (MD) simulations we show that (i) large clusters are only weakly outer ionized during laser excitation and (ii) relax to finite, ultracold Rydberg plasmas. Our explicit MD analysis reveals that DC-field induced frustrated recombination, i.e. field ionization of this peculiar cluster state in weak static external fields, is key to explaining the observed highly charged ions [4]. Routes for identifying Rydberg plasmas in clusters experimentally via electron spectroscopy will be proposed.

[1] T. Döppner et al., Phys. Rev. Lett. 105, 053401 (2010)

[2] T. Fennel et al., Phys. Rev. Lett. 99, 233401 (2010)

[3] T. Gorkhover et al., Phys. Rev. Lett. 108, 245005 (2012)

[4] C. Peltz, in preparation