Darmstadt 2008 – wissenschaftliches Programm
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A: Fachverband Atomphysik
A 10: Posters: Atomic clusters
A 10.13: Poster
Dienstag, 11. März 2008, 16:30–18:30, Poster C3
Clusters in Helium Droplets: Delaying the Coulomb Explosion in XFEL Pulses — •Christian Gnodtke, Ulf Saalmann, and Jan-Michael Rost — Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Straße 38, 01187 Dresden
In the context of atomic resolution, coherent diffractive imaging of non-periodic samples as suggested by Neutze et al. [1] we have simulated the explosion dynamics of rare-gas clusters embedded in Helium droplets and exposed to an intense XFEL (X-Ray Free Electron Laser) pulse. We find that the Coulomb explosion of the sample, which is the main limiting factor for this imaging technique, is significantly delayed in comparison to the case without Helium. Using quantum-mechanical transition rates for K-shell photo-ionization and Auger-decay, which are the main damage processes, combined with a molecular dynamics simulation of free electrons and ions we calculate the laser-induced dynamics of ArN and NeN clusters, with N=55-500, and assess the decline of image quality with longer pulse lengths. We find that, embedded in a Helium droplet, the positive charge that builds up in the cluster through photo-ionization and Auger-decay is efficiently transferred to the Helium shell by ionization of the Helium atoms in the Coulomb field of the charged cluster. The Helium shell then explodes while the cluster ions are efficiently screened from each other by the electrons originating from the Helium droplet, thus enhancing the stability of the cluster and improving the overall image quality in an imaging experiment.
[1] R. Neutze et al., Nature 406, 752 (2000)