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End date: 2024 × Start date: 2020 × DDC: 500 × Type: article × Publisher: Melville, NY : AIP Publishing LLC × Subject: Laser excitation ×

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    Spot profile analysis and lifetime mapping in ultrafast electron diffraction: Lattice excitation of self-organized Ge nanostructures on Si(001)
    (Melville, NY : AIP Publishing LLC, 2015) Frigge, T.; Hafke, B.; Tinnemann, V.; Witte, T.; Horn-von Hoegen, M.
    Ultrafast high energy electron diffraction in reflection geometry is employed to study the structural dynamics of self-organized Germanium hut-, dome-, and relaxed clusters on Si(001) upon femtosecond laser excitation. Utilizing the difference in size and strain state the response of hut- and dome clusters can be distinguished by a transient spot profile analysis. Surface diffraction from {105}-type facets provide exclusive information on hut clusters. A pixel-by-pixel analysis of the dynamics of the entire diffraction pattern gives time constants of 40, 160, and 390 ps, which are assigned to the cooling time constants for hut-, dome-, and relaxed clusters.
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    Transient magnetic gratings on the nanometer scale
    (Melville, NY : AIP Publishing LLC, 2020) Weder, D.; von Korff Schmising, C.; Günther, C.M.; Schneider, M.; Engel, D.; Hessing, P.; Strüber, C.; Weigand, M.; Vodungbo, B.; Jal, E.; Liu, X.; Merhe, A.; Pedersoli, E.; Capotondi, F.; Lüning, J.; Pfau, B.; Eisebitt, S.
    Laser-driven non-local electron dynamics in ultrathin magnetic samples on a sub-10 nm length scale is a key process in ultrafast magnetism. However, the experimental access has been challenging due to the nanoscopic and femtosecond nature of such transport processes. Here, we present a scattering-based experiment relying on a laser-induced electro- and magneto-optical grating in a Co/Pd ferromagnetic multilayer as a new technique to investigate non-local magnetization dynamics on nanometer length and femtosecond timescales. We induce a spatially modulated excitation pattern using tailored Al near-field masks with varying periodicities on a nanometer length scale and measure the first four diffraction orders in an x-ray scattering experiment with magnetic circular dichroism contrast at the free-electron laser facility FERMI, Trieste. The design of the periodic excitation mask leads to a strongly enhanced and characteristic transient scattering response allowing for sub-wavelength in-plane sensitivity for magnetic structures. In conjunction with scattering simulations, the experiment allows us to infer that a potential ultrafast lateral expansion of the initially excited regions of the magnetic film mediated by hot-electron transport and spin transport remains confined to below three nanometers.