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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.
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    Achieving diffraction-limited resolution in soft-X-ray Fourier-transform holography
    (Amsterdam : Elsevier Science, 2020) Geilhufe, Jan; Pfau, Bastian; Günther, Christian M.; Schneider, Michael; Eisebitt, Stefan
    The spatial resolution of microscopic images acquired via X-ray Fourier-transform holography is limited by the source size of the reference wave and by the numerical aperture of the detector. We analyze the interplay between both influences and show how they are matched in practice. We further identify, how high spatial frequencies translate to imaging artifacts in holographic reconstructions where mainly the reference beam limits the spatial resolution. As a solution, three methods are introduced based on numerical post-processing of the reconstruction. The methods comprise apodization of the hologram, refocusing via wave propagation, and deconvolution using the transfer function of the imaging system. In particular for the latter two, we demonstrate that image details smaller than the source size of the reference beam can be recovered up to the diffraction limit of the hologram. Our findings motivate the intentional application of a large reference-wave source enhancing the image contrast in applications with low photon numbers such as single-shot experiments at free-electron lasers or imaging at laboratory sources.