The Experts below are selected from a list of 4575 Experts worldwide ranked by ideXlab platform
Wolfgang Ludwig - One of the best experts on this subject based on the ideXlab platform.
-
x ray diffraction contrast tomography a novel technique for three dimensional grain mapping of polycrystals i direct Beam case
Journal of Applied Crystallography, 2008Co-Authors: Wolfgang Ludwig, Marcelo Goncalves Hönnicke, G Johnson, Andrew King, James MarrowAbstract:By simultaneous acquisition of the transmitted and the Diffracted Beams, the applicability of the previously introduced diffraction contrast tomography technique [Ludwig, Schmidt, Lauridsen & Poulsen (2008). J. Appl. Cryst. 41, 302–309] can be extended to the case of undeformed polycrystalline samples containing more than 100 grains per cross section. The grains are still imaged using the occasionally occurring diffraction contribution to the X-ray attenuation coefficient, which can be observed as a reduction in the intensity of the transmitted Beam when a grain fulfils the diffraction condition. Automating the segmentation of the extinction spot images is possible with the additional Diffracted Beam information, even in the presence of significant spot overlap. By pairing the corresponding direct (`extinction') and Diffracted Beam spots a robust sorting and indexing approach has been implemented. The analysis procedure is illustrated on a real data set and the result is validated by comparison with a two-dimensional grain map obtained by electron backscatter diffraction.
-
X-ray diffraction contrast tomography: a novel technique for three-dimensional grain mapping of polycrystals. I. Direct Beam case
Journal of Applied Crystallography, 2008Co-Authors: Wolfgang Ludwig, Søeren Schmidt, Erik Mejdal Lauridsen, Henning Friis PoulsenAbstract:The principles of a novel technique for nondestructive and simultaneous mapping of the three-dimensional grain and the absorption microstructure of a material are explained. The technique is termed X-ray diffraction contrast tomography, underlining its similarity to conventional X-ray absorption contrast tomography with which it shares a common experimental setup. The grains are imaged using the occasionally occurring diffraction contribution to the X-ray attenuation coefficient each time a grain fulfils the diffraction condition. The three-dimensional grain shapes are reconstructed from a limited number of projections using an algebraic reconstruction technique. An algorithm based on scanning orientation space and aiming at determining the corresponding crystallographic grain orientations is proposed. The potential and limitations of a first approach, based on the acquisition of the direct Beam projection images only, are discussed in this first part of the paper. An extension is presented in the second part of the paper [Johnson, King, Honnicke, Marrow & Ludwig (2008).J. Appl. Cryst.41, 310–318], addressing the case of combined direct and Diffracted Beam acquisition.
-
three dimensional imaging of crystal defects by topo tomography
Journal of Applied Crystallography, 2001Co-Authors: Wolfgang Ludwig, Peter Cloetens, J Hartwig, J Baruchel, B Hamelin, P BastieAbstract:A new technique, `topo-tomography', suitable for the characterization of the three-dimensional defect structure in bulk crystals, is proposed. The technique consists of the combination of diffraction topography and microtomography. It is applicable to high-quality single crystals, provided that the `direct image' is the dominant contrast mechanism. In this case, crystal defects give rise to locally enhanced intensity compared with the perfect-crystal matrix. The additional intensities sum along the Diffracted-Beam direction and yield projections of the local Bragg reflectivity. Like in the case of absorption tomography, the three-dimensional distribution of this reflectivity can be reconstructed from a large number of projections. The first experimental results of this technique, applied to a synthetic diamond crystal, are presented.
G. Ravichandran - One of the best experts on this subject based on the ideXlab platform.
-
pressure shear plate impact experiments on soda lime glass at pressures beyond 20 gpa
2019Co-Authors: Christian Kettenbeil, M Mello, Tong Jiao, R J Clifton, G. RavichandranAbstract:Recent modifications of a powder gun facility at Caltech have enabled pressure-shear plate impact (PSPI) experiments in a regime of pressures and strain rates that were previously inaccessible. A novel heterodyne Diffracted Beam photonic Doppler velocimeter (DPDV) has also been developed for simultaneous measurement of the normal and transverse particle velocity histories using the ±first order Diffracted Beams produced by a 400 lines/mm diffraction grating deposited onto the polished rear surface of the impacted target plate. We present and interpret the results of PSPI experiments conducted on 5 μm thick soda-lime glass samples subjected to normal stresses beyond 20 GPa and shear strain rates approaching 108 s−1. Transverse particle velocity measurements are used to infer the shearing resistance of soda-lime glass under these extreme conditions.
-
Heterodyne transverse velocimetry for pressure-shear plate impact experiments
Journal of Applied Physics, 2018Co-Authors: Christian Kettenbeil, Michael Mello, Moriah Bischann, G. RavichandranAbstract:Pressure-shear plate impact experiments have traditionally relied on free space Beam interferometers to measure transverse and normal particle velocities at the rear surface of the target plate. Here, we present two different interferometry schemes that leverage heterodyne techniques, which enable the simultaneous measurement of normal and transverse velocities using short-time Fourier transforms. Both techniques rely on Diffracted 1st order Beams that are generated by a specular, metallic grating deposited on the rear surface of the target plate. The Diffracted Beam photonic Doppler velocimetry technique interferes each 1st order Beam with a reference of slightly higher wavelength to create a constant carrier frequency at zero particle velocity. The second technique interferes the 1st order Beams with each other and employs an acousto-optic frequency shifter on the +1st order Beam to create a heterodyne transverse velocimeter. For both interferometer techniques, the 0th order Beam is interfered in a heterodyne photonic Doppler velocimetry arrangement to obtain a measurement of the normal particle velocity. An overview of both configurations is presented along with a derivation of the interferometer sensitivities to transverse and normal particle velocities as well as design guidelines for the optical system. Results from normal impact experiments conducted on Y-cut quartz are presented as the experimental validation of the two proposed techniques.
Henning Friis Poulsen - One of the best experts on this subject based on the ideXlab platform.
-
Reciprocal space mapping and strain scanning using X-ray diffraction microscopy
Journal of Applied Crystallography, 2018Co-Authors: Henning Friis Poulsen, P. K. Cook, H. Leemreize, Anders Pedersen, C. Yildirim, M. Kutsal, Anders Clemen Jakobsen, J. X. Trujillo, Jeppe Ormstrup, Carsten DetlefsAbstract:Dark-field X-ray microscopy is a new full-field imaging technique for nondestructively mapping the structure of deeply embedded crystalline elements in three dimensions. Placing an objective in the Diffracted Beam generates a magnified projection image of a local volume. By placing a detector in the back focal plane, high-resolution reciprocal space maps are generated for the local volume. Geometrical optics is used to provide analytical expressions for the resolution and range of the reciprocal space maps and the associated field of view in the sample plane. To understand the effects of coherence a comparison is made with wavefront simulations using the fractional Fourier transform. Reciprocal space mapping is demonstrated experimentally at an X-ray energy of 15.6 keV. The resolution function exhibits suppressed streaks and an FWHM resolution in all directions of ΔQ/Q = 4 × 10−5 or better. It is demonstrated by simulations that scanning a square aperture in the back focal plane enables strain mapping with no loss in resolution to be combined with a spatial resolution of 100 nm.
-
X-ray diffraction contrast tomography: a novel technique for three-dimensional grain mapping of polycrystals. I. Direct Beam case
Journal of Applied Crystallography, 2008Co-Authors: Wolfgang Ludwig, Søeren Schmidt, Erik Mejdal Lauridsen, Henning Friis PoulsenAbstract:The principles of a novel technique for nondestructive and simultaneous mapping of the three-dimensional grain and the absorption microstructure of a material are explained. The technique is termed X-ray diffraction contrast tomography, underlining its similarity to conventional X-ray absorption contrast tomography with which it shares a common experimental setup. The grains are imaged using the occasionally occurring diffraction contribution to the X-ray attenuation coefficient each time a grain fulfils the diffraction condition. The three-dimensional grain shapes are reconstructed from a limited number of projections using an algebraic reconstruction technique. An algorithm based on scanning orientation space and aiming at determining the corresponding crystallographic grain orientations is proposed. The potential and limitations of a first approach, based on the acquisition of the direct Beam projection images only, are discussed in this first part of the paper. An extension is presented in the second part of the paper [Johnson, King, Honnicke, Marrow & Ludwig (2008).J. Appl. Cryst.41, 310–318], addressing the case of combined direct and Diffracted Beam acquisition.
Christian Kettenbeil - One of the best experts on this subject based on the ideXlab platform.
-
pressure shear plate impact experiments on soda lime glass at pressures beyond 20 gpa
2019Co-Authors: Christian Kettenbeil, M Mello, Tong Jiao, R J Clifton, G. RavichandranAbstract:Recent modifications of a powder gun facility at Caltech have enabled pressure-shear plate impact (PSPI) experiments in a regime of pressures and strain rates that were previously inaccessible. A novel heterodyne Diffracted Beam photonic Doppler velocimeter (DPDV) has also been developed for simultaneous measurement of the normal and transverse particle velocity histories using the ±first order Diffracted Beams produced by a 400 lines/mm diffraction grating deposited onto the polished rear surface of the impacted target plate. We present and interpret the results of PSPI experiments conducted on 5 μm thick soda-lime glass samples subjected to normal stresses beyond 20 GPa and shear strain rates approaching 108 s−1. Transverse particle velocity measurements are used to infer the shearing resistance of soda-lime glass under these extreme conditions.
-
Heterodyne transverse velocimetry for pressure-shear plate impact experiments
Journal of Applied Physics, 2018Co-Authors: Christian Kettenbeil, Michael Mello, Moriah Bischann, G. RavichandranAbstract:Pressure-shear plate impact experiments have traditionally relied on free space Beam interferometers to measure transverse and normal particle velocities at the rear surface of the target plate. Here, we present two different interferometry schemes that leverage heterodyne techniques, which enable the simultaneous measurement of normal and transverse velocities using short-time Fourier transforms. Both techniques rely on Diffracted 1st order Beams that are generated by a specular, metallic grating deposited on the rear surface of the target plate. The Diffracted Beam photonic Doppler velocimetry technique interferes each 1st order Beam with a reference of slightly higher wavelength to create a constant carrier frequency at zero particle velocity. The second technique interferes the 1st order Beams with each other and employs an acousto-optic frequency shifter on the +1st order Beam to create a heterodyne transverse velocimeter. For both interferometer techniques, the 0th order Beam is interfered in a heterodyne photonic Doppler velocimetry arrangement to obtain a measurement of the normal particle velocity. An overview of both configurations is presented along with a derivation of the interferometer sensitivities to transverse and normal particle velocities as well as design guidelines for the optical system. Results from normal impact experiments conducted on Y-cut quartz are presented as the experimental validation of the two proposed techniques.
Carsten Detlefs - One of the best experts on this subject based on the ideXlab platform.
-
Reciprocal space mapping and strain scanning using X-ray diffraction microscopy
Journal of Applied Crystallography, 2018Co-Authors: Henning Friis Poulsen, P. K. Cook, H. Leemreize, Anders Pedersen, C. Yildirim, M. Kutsal, Anders Clemen Jakobsen, J. X. Trujillo, Jeppe Ormstrup, Carsten DetlefsAbstract:Dark-field X-ray microscopy is a new full-field imaging technique for nondestructively mapping the structure of deeply embedded crystalline elements in three dimensions. Placing an objective in the Diffracted Beam generates a magnified projection image of a local volume. By placing a detector in the back focal plane, high-resolution reciprocal space maps are generated for the local volume. Geometrical optics is used to provide analytical expressions for the resolution and range of the reciprocal space maps and the associated field of view in the sample plane. To understand the effects of coherence a comparison is made with wavefront simulations using the fractional Fourier transform. Reciprocal space mapping is demonstrated experimentally at an X-ray energy of 15.6 keV. The resolution function exhibits suppressed streaks and an FWHM resolution in all directions of ΔQ/Q = 4 × 10−5 or better. It is demonstrated by simulations that scanning a square aperture in the back focal plane enables strain mapping with no loss in resolution to be combined with a spatial resolution of 100 nm.
-
x ray diffraction microscopy based on refractive optics
Journal of Applied Crystallography, 2017Co-Authors: H F Poulsen, P. K. Cook, Anders Clemen Jakobsen, Hugh Simons, Sonja Rosenlund Ahl, Carsten DetlefsAbstract:A formalism is presented for dark-field X-ray microscopy using refractive optics. The new technique can produce three-dimensional maps of lattice orientation and axial strain within millimetre-sized sampling volumes and is particularly suited to in situ studies of materials at hard X-ray energies. An objective lens in the Diffracted Beam magnifies the image and acts as a very efficient filter in reciprocal space, enabling the imaging of individual domains of interest with a resolution of 100 nm. Analytical expressions for optical parameters such as numerical aperture, vignetting, and the resolution in both direct and reciprocal spaces are provided. It is shown that the resolution function in reciprocal space can be highly anisotropic and varies as a function of position in the field of view. Inserting a square aperture in front of the objective lens facilitates disjunct and space-filling sampling, which is key for three-dimensional reconstruction and analysis procedures based on the conservation of integrated intensity. A procedure for strain scanning is presented. Finally the formalism is validated experimentally at an X-ray energy of 17 keV.