Dynamics of the fragmentation and ionization of free metal clusters by mild femtosesond laser pulses

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Simple metal clusters with their free-electron-like electronic structure are ideal model systems to study few to many particle dynamcis. The collective electron resonance possible in such systems has a huge electric dipole; for light fields with the right frequency it acts as an antenna producing a strong local amplification of the electric field strength. Off resonance, on the other hand, close to the cluster external fields are significantly screened. This strong modification of the electromagnetic near field by the mobile electron cloud will have a decisive influence on the kinetic energy and angular distribution of emitted electrons or photofragments. In a joint experimental and theoretical study these effects will be examined in detail. Experimentally, the angular resolved kinetic energy distributions of photoelectrons and photofragments after femtosecond laser excitation of free, cold, size selected alkali and noble metal clusters will be measured. On the theory side, time-dependent density functional theory (TD-DFT) and time-dependent tight-binding (TDTB) combined with molecular dynamics calculations will be used to model these nonlinear ionization and fragmentation processes. Especially the newly developed TDTB-MD will allow detailed simulations on the long time scales relevant for fragmentation.