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- ItemAttosecond control of electron-ion recollision in high harmonic generation(Bristol : IOP, 2011) Gademann, G.; Kelkensberg, F.; Siu, W.K.; Johnsson, P.; Gaarde, M.B.; Schafer, K.J.; Vrakking, M.J.J.We show that high harmonic generation driven by an intense nearinfrared (IR) laser can be temporally controlled when an attosecond pulse train (APT) is used to ionize the generation medium, thereby replacing tunnel ionization as the first step in the well-known three-step model. New harmonics are formed when the ionization occurs at a well-defined time within the optical cycle of the IR field. The use of APT-created electron wave packets affords new avenues for the study and application of harmonic generation. In the present experiment, this makes it possible to study harmonic generation at IR intensities where tunnel ionization does not give a measurable signal.
- ItemInterference in strong-field ionization of a two-centre atomic system(College Park, MD : Institute of Physics Publishing, 2008) Ansari, Z.; Böttcher, M.; Manschwetus, B.; Rottke, H.; Sandner, W.; Verhoef, A.; Lezius, M.; Paulus, G.G.; Saenz, A.; Milošević, D.B.Strong-field photoionization of argon dimers by a few-cycle laser pulse is investigated using electron-ion coincidence momentum spectroscopy. The momentum distribution of the photoelectrons exhibits interference due to the emission from the two atomic argon centres, in analogy with a Young's doubleslit experiment. However, a simulation of the dimer photoelectron momentum spectrum based on the atomic spectrum supplemented with a theoretically derived interference term leads to distinct deviations from the experimental result. The deviations may have their origin in a complex electron dynamics during strong-field ionization of the Ar2 dimer. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.