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- ItemAttosecond time-resolved photoelectron holography([London] : Nature Publishing Group UK, 2018) Porat, G.; Alon, G.; Rozen, S.; Pedatzur, O.; Krüger, M.; Azoury, D.; Natan, A.; Orenstein, G.; Bruner, B.D.; Vrakking, M. J.J.; Dudovich, N.Ultrafast strong-field physics provides insight into quantum phenomena that evolve on an attosecond time scale, the most fundamental of which is quantum tunneling. The tunneling process initiates a range of strong field phenomena such as high harmonic generation (HHG), laser-induced electron diffraction, double ionization and photoelectron holography - all evolving during a fraction of the optical cycle. Here we apply attosecond photoelectron holography as a method to resolve the temporal properties of the tunneling process. Adding a weak second harmonic (SH) field to a strong fundamental laser field enables us to reconstruct the ionization times of photoelectrons that play a role in the formation of a photoelectron hologram with attosecond precision. We decouple the contributions of the two arms of the hologram and resolve the subtle differences in their ionization times, separated by only a few tens of attoseconds.
- ItemNanoplasmonic electron acceleration by attosecond-controlled forward rescattering in silver clusters([London] : Nature Publishing Group UK, 2017) Passig, Johannes; Zherebtsov, Sergey; Irsig, Robert; Arbeiter, Mathias; Peltz, Christian; Göde, Sebastian; Skruszewicz, Slawomir; Meiwes-Broer, Karl-Heinz; Tiggesbäumker, Josef; Kling, Matthias F.; Fennel, ThomasIn the strong-field photoemission from atoms, molecules, and surfaces, the fastest electrons emerge from tunneling and subsequent field-driven recollision, followed by elastic backscattering. This rescattering picture is central to attosecond science and enables control of the electron's trajectory via the sub-cycle evolution of the laser electric field. Here we reveal a so far unexplored route for waveform-controlled electron acceleration emerging from forward rescattering in resonant plasmonic systems. We studied plasmon-enhanced photoemission from silver clusters and found that the directional acceleration can be controlled up to high kinetic energy with the relative phase of a two-color laser field. Our analysis reveals that the cluster's plasmonic near-field establishes a sub-cycle directional gate that enables the selective acceleration. The identified generic mechanism offers robust attosecond control of the electron acceleration at plasmonic nanostructures, opening perspectives for laser-based sources of attosecond electron pulses.
- ItemAnisotropic photoemission time delays close to a Fano resonance([London] : Nature Publishing Group UK, 2018) Cirelli, Claudio; Marante, Carlos; Heuser, Sebastian; Petersson, C.L.M.; Galán, Álvaro Jiménez; Argenti, Luca; Zhong, Shiyang; Busto, David; Isinger, Marcus; Nandi, Saikat; Maclot, Sylvain; Rading, Linnea; Johnsson, Per; Gisselbrecht, Mathieu; Lucchini, Matteo; Gallmann, Lukas; Dahlström, J. Marcus; Lindroth, Eva; L’Huillier, Anne; Martín, Fernando; Keller, UrsulaElectron correlation and multielectron effects are fundamental interactions that govern many physical and chemical processes in atomic, molecular and solid state systems. The process of autoionization, induced by resonant excitation of electrons into discrete states present in the spectral continuum of atomic and molecular targets, is mediated by electron correlation. Here we investigate the attosecond photoemission dynamics in argon in the 20-40 eV spectral range, in the vicinity of the 3s -1 np autoionizing resonances. We present measurements of the differential photoionization cross section and extract energy and angle-dependent atomic time delays with an attosecond interferometric method. With the support of a theoretical model, we are able to attribute a large part of the measured time delay anisotropy to the presence of autoionizing resonances, which not only distort the phase of the emitted photoelectron wave packet but also introduce an angular dependence.
- ItemFew-femtosecond passage of conical intersections in the benzene cation([London] : Nature Publishing Group UK, 2017) Galbraith, M.C.E.; Scheit, S.; Golubev, N.V.; Reitsma, G.; Zhavoronkov, N.; Despré, V.; Lépine, F.; Kuleff, A.I.; Vrakking, M.J.J.; Kornilov, O.; Köppel, H.; Mikosch, J.Observing the crucial first few femtoseconds of photochemical reactions requires tools typically not available in the femtochemistry toolkit. Such dynamics are now within reach with the instruments provided by attosecond science. Here, we apply experimental and theoretical methods to assess the ultrafast nonadiabatic vibronic processes in a prototypical complex system - the excited benzene cation. We use few-femtosecond duration extreme ultraviolet and visible/near-infrared laser pulses to prepare and probe excited cationic states and observe two relaxation timescales of 11 ± 3 fs and 110 ± 20 fs. These are interpreted in terms of population transfer via two sequential conical intersections. The experimental results are quantitatively compared with state-of-the-art multi-configuration time-dependent Hartree calculations showing convincing agreement in the timescales. By characterising one of the fastest internal conversion processes studied to date, we enter an extreme regime of ultrafast molecular dynamics, paving the way to tracking and controlling purely electronic dynamics in complex molecules.
- ItemTracing dynamics of laser-induced fields on ultra-thin foils using complementary imaging with streak deflectometry(College Park, MD : American Physical Society, 2016) Abicht, Florian; Braenzel, Julia; Priebe, Gerd; Koschitzki, Christian; Andreev, Alexander; Nickles, Peter; Sander, Wolfgang; Schnürer, MatthiasWe present a detailed study of the electric and magnetic fields, which are created on plasma vacuum interfaces as a result of highly intense laser-matter interactions. For the field generation ultrathin polymer foils (30–50 nm) were irradiated with high intensity femtosecond (1019–1020 W/cm2) and picosecond (∼1017 W/cm2) laser pulses with ultrahigh contrast (1010–1011). To determine the temporal evolution and the spatial distribution of these fields the proton streak deflectometry method has been developed further and applied in two different imaging configurations. It enabled us to gather complementary information about the investigated field structure, in particular about the influence of different field components (parallel and normal to the target surface) and the impact of a moving ion front. The applied ultrahigh laser contrast significantly increased the reproducibility of the experiment and improved the accuracy of the imaging method. In order to explain the experimental observations, which were obtained by applying ultrashort laser pulses, two different analytical models have been studied in detail. Their ability to reproduce the streak deflectometry measurements was tested on the basis of three-dimensional particle simulations. A modification and combination of the two models allowed for an extensive and accurate reproduction of the experimental results in both imaging configurations. The controlled change of the laser pulse duration from 50 femtoseconds to 2.7 picoseconds led to a transition of the dominating force acting on the probing proton beam at the rear side of the polymer foil. In the picosecond case the (⇀vx⇀B)-term of the Lorentz force dominated over the counteracting ⇀E-field and was responsible for the direction of the net force. The applied proton deflectometry method allowed for an unambiguous determination of the magnetic field polarity at the rear side of the ultrathin foil.