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Abstract. Experiments have been performed to explore the potential of the low emittance 855 MeV electron beam of the Mainz Microtron MAMI for imaging with coherent X-rays. Transition radiation from a microfocused electron beam traversing a foil stack served as X-ray source with good transverse coherence. Refraction contrast radiographs of low absorbing materials, in particular polymer strings with diameters between 30 and 450 µm, were taken with a polychromatic transition radiation X-ray source with a spectral distribution in the energy range between 8 and about 40 keV. The electron beam spot size had standard deviation σ h = (8.6 ± 0.1) µm in the horizontal and σv = (7.5 ± 0.1) µm in the vertical direction. X-ray films were used as detectors. The source-to-detector distance amounted to 11.4 m. The objects were placed in a distance of up to 6 m from the X-ray film. Holograms of strings were taken with a beam spot size σv = (0.50 ± 0.05) µm in vertical direction, and a monochromatic X-ray beam of 6 keV energy. A good longitudinal coherence has been obtained by the (111) reflection of a flat silicon single crystal in Bragg geometry. It has been demonstrated that a direct exposure CCD chip with a pixel size of 13 × 13 µm 2 provides a highly efficient on-line detector. Contrast images can easily be generated with a complete elimination of all parasitic background. The on-line capability allows a minimization of the beam spot size by observing the smallest visible interference fringe spacings or the number of visible fringes. It has been demonstrated that X-ray films are also very useful detectors. The main advantage in comparison with the direct exposure CCD chip is the resolution. For the Structurix D3 (Agfa) X-ray film the standard deviation of the resolution was measured to be σ f = (1.2 ± 0.4) µm, which is about a factor of 6 better than for the direct exposure CCD chip. With the small effective X-ray spot size in vertical direction of σv = (1.2±0.3) µm and a geometrical magnification of up to 7.4 high-quality holograms of tiny transparent strings were taken in which the holographic information is contained in up to 18 interference fringes.PACS. 87.59.Bh X-ray radiography -52.59.Px Hard X-ray sources -41.50.+h X-ray beams and X-ray optics -07.85.Fv X-and gamma-ray sources, mirrors, gratings, and detectors -07.85.Nc X-ray and gamma-ray spectrometers

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