The Experts below are selected from a list of 228 Experts worldwide ranked by ideXlab platform

C Schulze - One of the best experts on this subject based on the ideXlab platform.

  • microfocusing of hard x rays with cylindrically bent crystal Monochromators
    Journal of Synchrotron Radiation, 1998
    Co-Authors: C Schulze, U. Lienert, M Hanfland, M Lorenzen, F Zontone
    Abstract:

    High-energy X-ray focusing with bent-crystal Monochromators is known to be hampered by so-called depth or crystal-thickness aberrations. A theoretical model of focus broadening based on the geometrical theory of X-ray diffraction in slightly deformed crystals is presented and compared with experimental data. First, it is shown that depth broadening can be avoided in the Laue geometry by an appropriate choice of asymmetry angle. Based on this finding, a monochromator for high-pressure diffraction experiments has been designed and a source-size-limited focal spot below 10 microns is observed. As a consequence of the box-shaped rocking curve of bent Laue crystals, the focus is free of long-ranging tails. Diffraction patterns of standard powder samples were recorded on imaging plates and a theoretical description of the energy-dispersion-related peak broadening is given. Finally, diffraction patterns of N2 at 180 kbar demonstrate the excellent data quality achievable with this monochromator.

  • fixed exit Monochromators for high energy synchrotron radiation
    Journal of Synchrotron Radiation, 1995
    Co-Authors: P. Suortti, C Schulze
    Abstract:

    Current developments in X-ray optics for synchrotron radiation beamlines are briefly reviewed. Reference is made to recent work on adaptive mirrors, cryogenic cooling of Monochromators, use of thin diamond crystals, and active correction of the crystal shape for distortions caused by beam heating. The use of bent Si crystals as Monochromators is discussed in detail. At high energies Si crystals become transparent to X-rays allowing new monochromator constructions. Bending of the crystal increases the energy bandpass and allows focusing. Different combinations of bent crystals that provide a fixed exit beam are discussed. These include vertically diffracting meridionally focusing Laue–Laue crystals, a Laue crystal combined with a sagittally focusing Bragg crystal, and a Laue–Bragg pair of crystals which provides meridional focusing at two stages.

Timm Weitkamp - One of the best experts on this subject based on the ideXlab platform.

  • micro imaging performance of multilayers used as Monochromators for coherent hard x ray synchrotron radiation
    Proceedings of SPIE, 2010
    Co-Authors: Alexander Rack, Timm Weitkamp, M Riotte, T Rack, R Dietsch, T Holz, M Kramer, Frank Siewert, M Meduna, Ch Morawe
    Abstract:

    We present a systematic study in which multilayers of different composition (W/Si, Mo/Si, Pd/B 4 C), periodicity (from 2.5 to 5.5 nm), and numbers of layers have been characterised. Particularly, we investigated the intrinsic quality (roughness and reflectivity) as well as the performance (flatness and coherence of the outgoing beam) as a monochromator for synchrotron radiation hard X-ray micro-imaging. The results indicate that the material composition is the dominating factor for the performance. This is of high importance for synchrotron-based hard X-ray imaging which has become a widely applied tool for probing the microstructure of bulk samples. The high spatial resolution and different contrast modalities available here strongly depend on using coherent beams from highly brilliant sources. In order to satisfy the demand for a high flux of quasi-monochromatic photons, multilayer-coated mirrors are commonly used as Monochromators. Their properties present a good tradeoff between spectral bandwidth and photon flux density. Since the photon flux density at the sample position is higher than with standard crystal Monochromators, better spatial resolution can be reached. This comes at the cost of reduced energy resolution and stronger non-uniformities in the incoming beam profile. By helping scientists and engineers specify the design parameters of multilayer Monochromators, our results can contribute to a better exploitation of the advantages of multilayer Monochromators over crystal-based devices; i.e., larger spectral bandwidth and high photon flux density for X-ray imaging.

  • comparative study of multilayers used in Monochromators for synchrotron based coherent hard x ray imaging
    Journal of Synchrotron Radiation, 2010
    Co-Authors: Timm Weitkamp, Alexander Rack, M Riotte, D Grigoriev, T Rack, Lukas Helfen, Tilo Baumbach, R Dietsch
    Abstract:

    A systematic study is presented in which multilayers of different composition (W/Si, Mo/Si, Pd/B4C), periodicity (from 2.5 to 5.5 nm) and number of layers have been characterized. In particular, the intrinsic quality (roughness and reflectivity) as well as the performance (homogeneity and coherence of the outgoing beam) as a monochromator for synchrotron radiation hard X-ray micro-imaging are investigated. The results indicate that the material composition is the dominating factor for the performance. By helping scientists and engineers specify the design parameters of multilayer Monochromators, these results can contribute to a better exploitation of the advantages of multilayer Monochromators over crystal-based devices; i.e. larger spectral bandwidth and high photon flux density, which are particularly useful for synchrotron-based micro-radiography and -tomography.

  • coherence and wavefront characterization of si 111 Monochromators using double grating interferometry
    Journal of Synchrotron Radiation, 2010
    Co-Authors: Ana Diaz, Cristian Mocuta, Julian Stangl, Mario Keplinger, Timm Weitkamp, Franz Pfeiffer, Christian David, T H Metzger
    Abstract:

    A study of the coherence and wavefront properties of a pseudo-channel-cut monochromator in comparison with a double-crystal monochromator is presented. Using a double-grating interferometer designed for the hard X-ray regime, the complex coherence factor was measured and the wavefront distortions at the sample position were analyzed. A transverse coherence length was found in the vertical direction that was a factor of two larger for the channel-cut monochromator owing to its higher mechanical stability. The wavefront distortions after different optical elements in the beam, such as Monochromators and mirrors, were also quantified. This work is particularly relevant for coherent diffraction imaging experiments with synchrotron sources.

P. Suortti - One of the best experts on this subject based on the ideXlab platform.

  • fixed exit Monochromators for high energy synchrotron radiation
    Journal of Synchrotron Radiation, 1995
    Co-Authors: P. Suortti, C Schulze
    Abstract:

    Current developments in X-ray optics for synchrotron radiation beamlines are briefly reviewed. Reference is made to recent work on adaptive mirrors, cryogenic cooling of Monochromators, use of thin diamond crystals, and active correction of the crystal shape for distortions caused by beam heating. The use of bent Si crystals as Monochromators is discussed in detail. At high energies Si crystals become transparent to X-rays allowing new monochromator constructions. Bending of the crystal increases the energy bandpass and allows focusing. Different combinations of bent crystals that provide a fixed exit beam are discussed. These include vertically diffracting meridionally focusing Laue–Laue crystals, a Laue crystal combined with a sagittally focusing Bragg crystal, and a Laue–Bragg pair of crystals which provides meridional focusing at two stages.

J Hrdý - One of the best experts on this subject based on the ideXlab platform.

  • Refraction in general asymmetric X-ray Bragg diffraction.
    Journal of Synchrotron Radiation, 2001
    Co-Authors: J Hrdý
    Abstract:

    When the surface of a single-crystal monochromator is not parallel to the diffracting crystallographic planes, the diffracted beam is generally deviated from the plane of diffraction and the angle between the diffracted beam and the diffracting planes is different from the angle between the incident beam and the diffracting planes. The angular diffraction regions for the incident and diffracted beams are also different. This is the manifestation of the refraction occurring during Bragg diffraction. Very simple formulae are presented which describe this situation in a general case (e.g. for a rotated-inclined X-ray monochromator). These formulae allow sagittally focusing Monochromators for synchrotron radiation to be easily designed, based on X-ray diffraction–refraction phenomena. Some important properties of such types of Monochromators are deduced.

  • Rotated-inclined double-crystal monochromator for synchrotron radiation: aberration and its compensation.
    Journal of synchrotron radiation, 1998
    Co-Authors: J Hrdý, E Busetto
    Abstract:

    A rotated-inclined double-crystal X-ray monochromator was designed for high-power undulator beamlines for SPring-8 to reduce the impinging radiation power density. Recently, it has been shown that an inclined double-crystal monochromator suffers from a certain type of geometrical aberration that may be relatively easily compensated. In this paper, it is shown that a similar aberration exists also in the case of rotated-inclined Monochromators and that as in the inclined case the aberration may also be compensated.

T Ishikawa - One of the best experts on this subject based on the ideXlab platform.