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search.filters.applied.f.access: openAccess × End date: 2024 × Start date: 2020 × DDC: 500 × Publisher: Melville, NY : AIP Publishing LLC ×

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Now showing 1 - 5 of 5
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    Imaging plasma formation in isolated nanoparticles with ultrafast resonant scattering
    (Melville, NY : AIP Publishing LLC, 2020) Rupp, Daniela; Flückiger, Leonie; Adolph, Marcus; Colombo, Alessandro; Gorkhover, Tais; Harmand, Marion; Krikunova, Maria; Müller, Jan Philippe; Oelze, Tim; Ovcharenko, Yevheniy; Richter, Maria; Sauppe, Mario; Schorb, Sebastian; Treusch, Rolf; Wolter, David; Bostedt, Christoph; Möller, Thomas
    We have recorded the diffraction patterns from individual xenon clusters irradiated with intense extreme ultraviolet pulses to investigate the influence of light-induced electronic changes on the scattering response. The clusters were irradiated with short wavelength pulses in the wavelength regime of different 4d inner-shell resonances of neutral and ionic xenon, resulting in distinctly different optical properties from areas in the clusters with lower or higher charge states. The data show the emergence of a transient structure with a spatial extension of tens of nanometers within the otherwise homogeneous sample. Simulations indicate that ionization and nanoplasma formation result in a light-induced outer shell in the cluster with a strongly altered refractive index. The presented resonant scattering approach enables imaging of ultrafast electron dynamics on their natural timescale.
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    Highly efficient soft x-ray spectrometer for transient absorption spectroscopy with broadband table-top high harmonic sources
    (Melville, NY : AIP Publishing LLC, 2021) Kleine, Carlo; Ekimova, Maria; Winghart, Marc-Oliver; Eckert, Sebastian; Reichel, Oliver; Löchel, Heike; Probst, Jürgen; Braig, Christoph; Seifert, Christian; Erko, Alexei; Sokolov, Andrey; Vrakking, Marc J. J.; Nibbering, Erik T. J.; Rouzée, Arnaud
    We present a novel soft x-ray spectrometer for ultrafast absorption spectroscopy utilizing table-top femtosecond high-order harmonic sources. Where most commercially available spectrometers rely on spherical variable line space gratings with a typical efficiency on the order of 3% in the first diffractive order, this spectrometer, based on a Hettrick-Underwood design, includes a reflective zone plate as a dispersive element. An improved efficiency of 12% at the N K-edge is achieved, accompanied by a resolving power of 890. The high performance of the soft x-ray spectrometer is further demonstrated by comparing nitrogen K-edge absorption spectra from calcium nitrate in aqueous solution obtained with our high-order harmonic source to previous measurements performed at the electron storage ring facility BESSY II.
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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.
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    Toward ultrafast magnetic depth profiling using time-resolved x-ray resonant magnetic reflectivity
    (Melville, NY : AIP Publishing LLC, 2021) Chardonnet, Valentin; Hennes, Marcel; Jarrier, Romain; Delaunay, Renaud; Jaouen, Nicolas; Kuhlmann, Marion; Ekanayake, Nagitha; Léveillé, Cyril; von Korff Schmising, Clemens; Schick, Daniel; Yao, Kelvin; Liu, Xuan; Chiuzbăian, Gheorghe S.; Lüning, Jan; Vodungbo, Boris; Jal, Emmanuelle
    During the last two decades, a variety of models have been developed to explain the ultrafast quenching of magnetization following femtosecond optical excitation. These models can be classified into two broad categories, relying either on a local or a non-local transfer of angular momentum. The acquisition of the magnetic depth profiles with femtosecond resolution, using time-resolved x-ray resonant magnetic reflectivity, can distinguish local and non-local effects. Here, we demonstrate the feasibility of this technique in a pump–probe geometry using a custom-built reflectometer at the FLASH2 free-electron laser (FEL). Although FLASH2 is limited to the production of photons with a fundamental wavelength of 4 nm (≃310 eV), we were able to probe close to the Fe L3 edge (706.8 eV) of a magnetic thin film employing the third harmonic of the FEL. Our approach allows us to extract structural and magnetic asymmetry signals revealing two dynamics on different time scales which underpin a non-homogeneous loss of magnetization and a significant dilation of 2 Å of the layer thickness followed by oscillations. Future analysis of the data will pave the way to a full quantitative description of the transient magnetic depth profile combining femtosecond with nanometer resolution, which will provide further insight into the microscopic mechanisms underlying ultrafast demagnetization.
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    Reciprocal space slicing: A time-efficient approach to femtosecond x-ray diffraction
    (Melville, NY : AIP Publishing LLC, 2021) Zeuschner, S.P.; Mattern, M.; Pudell, J.-E.; von Reppert, A.; Rössle, M.; Leitenberger, W.; Schwarzkopf, J.; Boschker, J.E.; Herzog, M.; Bargheer, M.
    An experimental technique that allows faster assessment of out-of-plane strain dynamics of thin film heterostructures via x-ray diffraction is presented. In contrast to conventional high-speed reciprocal space-mapping setups, our approach reduces the measurement time drastically due to a fixed measurement geometry with a position-sensitive detector. This means that neither the incident (ω) nor the exit ( 2θ ) diffraction angle is scanned during the strain assessment via x-ray diffraction. Shifts of diffraction peaks on the fixed x-ray area detector originate from an out-of-plane strain within the sample. Quantitative strain assessment requires the determination of a factor relating the observed shift to the change in the reciprocal lattice vector. The factor depends only on the widths of the peak along certain directions in reciprocal space, the diffraction angle of the studied reflection, and the resolution of the instrumental setup. We provide a full theoretical explanation and exemplify the concept with picosecond strain dynamics of a thin layer of NbO2.