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Monochromatic Beam (monochromatic + beam)
Selected AbstractsDetermination of directionally dependent structural and microstructural information using high-energy X-ray diffractionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2008J. E. Daniels High-energy synchrotron X-ray diffraction using a monochromatic beam and large area detector offers a unique method for the study of directionally dependent sample information. The very short wavelengths and subsequent low scattering angles mean that scattering vectors at all angles approximately perpendicular to the beam direction are sampled simultaneously. Here a method is proposed and demonstrated in which the magnitude and directions of structural and microstructural changes can be determined with higher resolution than was possible with previously used techniques. The method takes advantage of parametric refinements over multiple data sets using the profile fitting package TOPAS. Examples of the technique applied to the study of strains in multiphase zirconium alloys and microstructural texture in ferroelastic/ferroelectric ceramics are given. The angular precision in lattice strain for a diffraction image with good statistics is found to be below 0.1°. [source] Improvement of SAXS measurements on Kratky slit systems by Göbel mirrors and imaging-plate detectorsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-2 2000Alexander Bergmann Laboratory X-ray sources emit a highly divergent beam. The Kratky compact camera is constructed to maximize the intensity in the sample using a slit collimation system. The performance of this camera can be further increased if the primary beam is collimated from a divergent into a parallel beam. A recently developed device for this purpose is the so-called `Göbel mirror'. This mirror is made of parabolically bent multilayers, designed to collimate divergent X-rays from laboratory X-ray sources into a parallel and monochromatic beam of high brilliance. Modification of the block collimation system in combination with a Göbel mirror leads to a different beam geometry, resulting in an intensity increase by a factor of about 10. The gain in intensity implicates the use of imaging-plate detectors, which have a wide linear range in intensity and allow the full use of the increased intensity. Hence the quality of the SAXS data is improved by the higher intensity primary beam, the much lower background due to the exclusive use of Cu K, radiation, and a detection unit which is linear in the measured intensity regime. All these advantages, such as intensity gain, lower background, better quality of the data, are demonstrated with some selected experimental results. [source] Radiation damage of protein crystals at cryogenic temperatures between 40,K and 150,KJOURNAL OF SYNCHROTRON RADIATION, Issue 4 2002Tsu-Yi Teng X-ray radiation damage of lysozyme single crystals by an intense monochromatic beam from the Advanced Photon Source is studied at cryogenic temperatures between 40,K and 150,K. The results confirm that primary radiation damage is both linearly dependent on the X-ray dose and independent of temperature. The upper limit for the primary radiation damage observed in our previous study [Teng & Moffat (2000), J. Synchrotron Rad. 7, 313317] holds over the wider temperature range of this study. The X-ray diffraction quality of the data acquired at 40,K is superior to those at 100,K, apparently due to temperature dependence of secondary and tertiary radiation damage and to reduced thermal motion. [source] Coherence control of electron spin currents in semiconductorsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2006Henry M. van Driel Abstract We provide an overview of some of our recent work on the use of one color and two color optical techniques to generate and control electronic spin currents in semiconductors for which a spin,orbit interaction exists. The generation process relies on the quantum interference between different absorption pathways, such as that between single and two photon absorption or those involving different polarization states of a monochromatic beam. For different crystal orientations and/or beam polarizations it is possible to generate a spin current with or without an electric current, and an electrical current with or without a spin current. In our experiments, which are conducted either at 80 K or 295 K, we typically employ nominally 100 fs pulses centered near 1500 and 750 nm. The currents generated are quasi-ballistic and the carriers typically move distances of ,1,10 nm, determined by the momentum relaxation time, which is of the order of 100 fs. The transient characteristics of spin-polarized electrical currents generated in strained GaAs at room temperature by ,100 fs pulses is detected by the emitted THz radiation. Pure spin currents can be detected by taking advantage of the accumulation of up and down spins on opposite sides of tightly focused pump beams. The spin states are detected through differential transmission measurements of tightly focused right and left circularly polarized, near-band-edge probe pulses, delayed by several picoseconds from the pump pulses to allow carrier thermalization to occur. By spatial scanning across the differential spin profiles and determining the amplitude of the response we are able to translate this into nm spatial resolution of spin displacement. Finally, the ability to generate ballistic currents using purely optical techniques allows us to generate transverse Hall-like currents, with transverse charge currents generated from pure spin currents and transverse spin currents generated from pure charge currents. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High-resolution study of dynamical diffraction phenomena accompanying the Renninger (222/113) case of three-beam diffraction in siliconACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2010A. Kazimirov X-ray optical schemes capable of producing a highly monochromatic beam with high angular collimation in both the vertical and horizontal planes have been evaluated and utilized to study high-resolution diffraction phenomena in the Renninger (222/113) case of three-beam diffraction in silicon. The effect of the total reflection of the incident beam into the nearly forbidden reflected beam was observed for the first time with the maximum 222 reflectivity at the 70% level. We have demonstrated that the width of the 222 reflection can be varied many times by tuning the azimuthal angle by only a few µrad in the vicinity of the three-beam diffraction region. This effect, predicted theoretically more than 20 years ago, is explained by the enhancement of the 222 scattering amplitude due to the virtual two-stage 000 113 222 process which depends on the azimuthal angle. [source] Small-angle energy-dispersive X-ray scattering using a laboratory-based diffractometer with a conventional sourceJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2007Giuseppe Portale The use of polychromatic Bremsstrahlung X-rays generated by commercial tubes for energy-dispersive small-angle scattering measurements has not been extensively discussed in the literature, mainly because of some difficulties associated with it. If a suitable experimental setup is chosen and concomitant phenomena are taken into account for correcting the observed X-ray patterns, energy-dispersive small-angle X-ray scattering (SAXS) may become an interesting alternative to conventional measurements based on monochromatic beams. Energy-dispersive SAXS experiments carried out on protein solutions, micelles, semicrystalline polymers and catalytic systems are discussed to illustrate the new opportunities offered by this technique as well as its limitations. [source] 4241: Optical characterization of PCOACTA OPHTHALMOLOGICA, Issue 2010TJTP VAN DEN BERG Purpose Opacification of the posterior capsule (PCO) is known to degrade visual function on both counts: small angle resolution (visual acuity and contrast sensitivity) as well as large angle light scatter (straylight). No studies have been performed to delineate the optical characteristics of PCO as a basis for explanation of these visual function defects. Methods Preparations of IOL-capsule combinations were harvested from donor eyes after removal of the cornea. They were mounted submersed in saline in an optical set-up, used earlier to characterize the optics of the crystalline lens (van den Berg et al. VR 1999). Illuminated by monochromatic beams of light, the light spreading originating from different areas of the preparation was measured as function of wavelength for different angles. Based on physical optics theory, the optical characteristics of PCO was derived. The data will be presented translated into the straylight parameter, directly comparable to the figures obtained in vivo using the clinical straylight meter (C-Quant from Oculus). Results Twenty successful preparations were harvested with at least some PCO areas. PCO grades varied from severe to slight. Two physically different types of light spreading could be discriminated. One type corresponding to pearl-like appearance, characterized by little wavelenght dependence and smal angle dominance. The other type corresponding to diffuse scatter, characterized by strong wavelength dependence and large angle dominance. The scatter values measured corresponded to clinical measures of straylight in PCO patients using the C-Quant. Conclusion The light scattering characteristics of PCO show two types of optical disturbance: a refractile type, probably dominated by pearl-like structures, and a diffuse type of scattering of yet unclear origin. [source] | ||||||||||