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A: Fachverband Atomphysik
A 16: Atomic Clusters
A 16.5: Vortrag
Donnerstag, 13. März 2008, 09:30–09:45, 3D
Higly charged ions from laser cluster interactions — •Thomas Fennel1,2, Lora Ramunno2, and Thomas Brabec2 — 1Institute of Physics, University of Rostock — 2Center for Photonics, Ottawa
Today it is widely accepted that resonant plasmon excitations and efficient heating through inverse bremsstrahlung are the dominant mechanisms for the highly efficient absorption of intense IR femtosecond laser pulses by atomic cluster. From experiments it is known that independent of the type of material, intermediate and heavy atom clusters emit ions with high charge states of up q=20-30 already at moderate laser intensities between 1014−1015 W/cm2. This has been demonstrated e.g. for XeN, PtN, and PbN. The mechanisms underlying the generation of the measured high ionic charge states, however, is still under discussion. Our molecular dynamics analysis of Xe clusters identifies two physical mechanisms that contribute to this yet unexplained observation of extremely high ionic charge states at moderate laser intensity [1]. First, the local cluster electric field supports electron impact ionization and increases the highest ion charge state by up to 40%. Second, the ion charge distribution of the nanoplasma is only weakly affected by electron-ion recombination, as recombination is frustrated by the background electric fields typically used in ion detectors. This increases the highest charge state by up to 90%, as compared to the usually assumed recombination of all electrons trapped in the cluster potential. Both effects together augment the highest charge state by up to a factor of 2 and beyond, in reasonable agreement with experiments. [1] T. Fennel et al., accepted for Phys. Rev. Lett., 2007