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  • 1
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    An accurate theory of X-ray coplanar multiple SRMS diffractometry (2018)
    International Union of Crystallography
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    Publication Date: 2018-10-04
    Description: The article reports an accurate theory of X-ray coplanar multiple diffraction for an experimental setup that consists of a generic synchrotron radiation (SR) source, double-crystal monochromator (M) and slit (S). It is called for brevity the theory of X-ray coplanar multiple SRMS diffractometry. The theory takes into account the properties of synchrotron radiation as well as the features of diffraction of radiation in the monochromator crystals and the slit. It is shown that the angular and energy dependence (AED) of the sample reflectivity registered by a detector has the form of a convolution of the AED in the case of the monochromatic plane wave with the instrumental function which describes the angular and energy spectrum of radiation incident on the sample crystal. It is shown that such a scheme allows one to measure the rocking curves close to the case of the monochromatic incident plane wave, but only using the high-order reflections by monochromator crystals. The case of four-beam (220)(331)({overline {11}}1) diffraction in Si is considered in detail.
    Electronic ISSN: 2053-2733
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by International Union of Crystallography
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  • 2
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    Computer simulations of X-ray spherical wave dynamical diffraction in one and two crystals in the Laue case (2018)
    International Union of Crystallography
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    Publication Date: 2018-10-12
    Description: This article reports computer simulations of X-ray spherical wave dynamical diffraction in one and two single crystals in the Laue case. An X-ray compound refractive lens (CRL) as a secondary radiation source of spherical waves was considered for the first time and in contrast to previous simulations with the assumption of the use of a slit. The main properties of the CRL as a secondary source are discussed and two focusing phenomena are analysed. The first one is the diffraction focusing effect for one single crystal in the reflected beam and in the case of a large source-to-detector distance. The second one is the same but for two single crystals and for the twice-reflected beam in the case of a short distance between the source and detector. The first effect is well pronounced in the case of strong absorption. However, it may also be used as an element of an energy spectrometer in the medium and even weak absorption case. The second effect will appear in the case of weak absorption. It is shown that it is not effective to use it in an energy spectrometer. In the case of weak absorption the transverse size of the diffraction focused beam will oscillate together with the reflected beam integral intensity. The oscillation period is close to the extinction length.
    Electronic ISSN: 2053-2733
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by International Union of Crystallography
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  • 3
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    Transmission of an X-ray beam through a two-dimensional photonic crystal and the Talbot effect (2018)
    International Union of Crystallography
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    Publication Date: 2018-02-15
    Description: Results of computer simulations of the transmission of an X-ray beam through a two-dimensional photonic crystal as well as the propagation of an X-ray beam in free space behind the photonic crystal are reported. The photonic crystal consists of a square lattice of silicon cylinders of diameter 0.5 µm. The amount of matter in the path of the X-ray beam rapidly decreases at the sides of the cylinder projections. Therefore the transmission is localized near the boundaries, and appears like a channeling effect. The iterative method of computer simulations is applied. This method is similar to the multi-slice method that is widely used in electron microscopy. It allows a solution to be obtained with acceptable accuracy. A peculiarity in the intensity distribution inside the Talbot periodzTin free space was found when the intensity is approximately equal to the initial value at a distance 0.46zT, and it is shifted by half a period at distance 0.5zT. The reason for this effect is the existence of a periodic phase of the wavefunction of radiation inside the intensity peaks. Simulations with zero phase do not show this effect. Symmetry rules for the Talbot effect are discussed.
    Print ISSN: 0909-0495
    Electronic ISSN: 1600-5775
    Topics: Geosciences , Physics
    Published by International Union of Crystallography
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  • 4
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    Rocking curve and spatial coherence properties of a long X-ray compound refractive lens (2018)
    International Union of Crystallography
    Details
    Publication Date: 2018-10-05
    Description: Semi-analytical theory of a long set of X-ray compound refractive lenses (CRLs) based on recurrence relations is developed further. The geometrical aperture, angular divergence of incident radiation and source size were accurately taken into account. Using this theory it is possible to calculate the width of the rocking curve of a long (40.7 cm) Be CRL which coincides with experimental data obtained earlier. By this approach the transverse coherence length for the X-ray beam after passing a set of CRLs of arbitrary complexity has been estimated. It is shown that at the focus this coherence length is equal to a diffraction-limited beam size (beam size in the case of a point source) and has minimal difference with the real beam size.
    Print ISSN: 0909-0495
    Electronic ISSN: 1600-5775
    Topics: Geosciences , Physics
    Published by International Union of Crystallography
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