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Author: Pfau, Bastian × Author: Schneider, Michael × End date: 2019 × Start date: 2017 × WGL Institute: MBI ×

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Now showing 1 - 4 of 4
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    Experimental evaluation of signal-to-noise in spectro-holography via modified uniformly redundant arrays in the soft x-ray and extreme ultraviolet spectral regime
    (Bristol : IOP Publ., 2017-05-08) Günther, Christian M.; Guehrs, Erik; Schneider, Michael; Pfau, Bastian; von Korff Schmising, Clemens; Geilhufe, Jan; Schaffert, Stefan; Eisebitt, Stefan
    We present dichroic x-ray lensless magnetic imaging by Fourier transform holography with an extended reference scheme via a modified uniformly redundant array (mURA). Holographic images of magnetic domains simultaneously generated by a single pinhole reference as well as by a mURA reference are compared with respect to the signal-to-noise ratio (SNR) as a function of exposure time. We apply this approach for spectro-holographic imaging of ferromagnetic domain patterns in Co/Pt multilayer films. Soft x-rays with wavelengths of 1.59 nm (Co L3 absorption edge) and 20.8 nm (Co M2,3 absorption edges) are used for image formation and to generate contrast via x-ray magnetic circular dichroism. For a given exposure time, the mURA-based holography allows to decouple the reconstruction SNR from the spatial resolution. For 1.59 nm wavelength, the reconstruction via the extended reference scheme shows no significant loss of spatial resolution compared to the single pinhole reference. In contrast, at 20.8 nm wavelength the single pinhole reveals some very intricate features which are lost in the image generated by the mURA, although overall a high-quality image is generated. The SNR-advantage of the mURA scheme is most notable when the hologram has to be encoded with few photons, while errors associated with the increased complexity of the reconstruction process reduce the advantage for high-photon-number experiments.
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    In situ single-shot diffractive fluence mapping for X-ray free-electron laser pulses
    ([London] : Nature Publishing Group UK, 2018) Schneider, Michael; Günther, Christian M.; Pfau, Bastian; Capotondi, Flavio; Manfredda, Michele; Zangrando, Marco; Mahne, Nicola; Raimondi, Lorenzo; Pedersoli, Emanuele; Naumenko, Denys; Eisebitt, Stefan
    Free-electron lasers (FELs) in the extreme ultraviolet (XUV) and X-ray regime opened up the possibility for experiments at high power densities, in particular allowing for fluence-dependent absorption and scattering experiments to reveal non-linear light-matter interactions at ever shorter wavelengths. Findings of such non-linear effects are met with tremendous interest, but prove difficult to understand and model due to the inherent shot-to-shot fluctuations in photon intensity and the often structured, non-Gaussian spatial intensity profile of a focused FEL beam. Presently, the focused beam is characterized and optimized separately from the actual experiment. Here, we present the simultaneous measurement of XUV diffraction signals from solid samples in tandem with the corresponding single-shot spatial fluence distribution on the actual sample. Our in situ characterization scheme enables direct monitoring of the sample illumination, providing a basis to optimize and quantitatively understand FEL experiments.
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    Generating circularly polarized radiation in the extreme ultraviolet spectral range at the free-electron laser FLASH
    (Melville, NY : American Institute of Physics, 2017) von Korff Schmising, Clemens; Weder, David; Noll, Tino; Pfau, Bastian; Hennecke, Martin; Strüber, Christian; Radu, Ilie; Schneider, Michael; Staeck, Steffen; Günther, Christian M.; Lüning, Jan; Merhe, Alaa el dine; Buck, Jens; Hartmann, Gregor; Viefhaus, Jens; Treusch, Rolf; Eisebitt, Stefan
    A new device for polarization control at the free electron laser facility FLASH1 at DESY has been commissioned for user operation. The polarizer is based on phase retardation upon reflection off metallic mirrors. Its performance is characterized in three independent measurements and confirms the theoretical predictions of efficient and broadband generation of circularly polarized radiation in the extreme ultraviolet spectral range from 35 eV to 90 eV. The degree of circular polarization reaches up to 90% while maintaining high total transmission values exceeding 30%. The simple design of the device allows straightforward alignment for user operation and rapid switching between left and right circularly polarized radiation.
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    Multi-color imaging of magnetic Co/Pt heterostructures
    (Melville, NY : AIP Publishing LLC, 2017) Willems, Felix; von Korff Schmising, Clemens; Weder, David; Günther, Christian M.; Schneider, Michael; Pfau, Bastian; Meise, Sven; Guehrs, Erik; Geilhufe, Jan; Merhe, Alaa El Din; Jal, Emmanuelle; Vodungbo, Boris; Lüning, Jan; Mahieu, Benoit; Capotondi, Flavio; Pedersoli, Emanuele; Gauthier, David; Manfredda, Michele; Eisebitt, Stefan
    We present an element specific and spatially resolved view of magnetic domainsin Co/Pt heterostructures in the extreme ultraviolet spectral range. Resonantsmall-angle scattering and coherent imaging with Fourier-transform holographyreveal nanoscale magnetic domain networks via magnetic dichroism of Co at theM2,3 edges as well as via strong dichroic signals at the O2,3 and N6,7 edges of Pt.We demonstrate for the first time simultaneous, two-color coherent imaging at afree-electron laser facility paving the way for a direct real space access toultrafast magnetization dynamics in complex multicomponent material systems.