No 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.

No abstract

A tunable Laue/bent-Laue monochromator with fixed second crystal for synchrotron radiation AIP Conf.

Novel focusing optical devices have been developed for synchrotron radiation in the energy range 40-100 keV. Firstly, a narrow-band-pass focusing energy-tuneable fixed-exit monochromator was constructed by combining meridionally bent Laue and Bragg crystals. Dispersion compensation was applied to retain the high momentum resolution despite the beam divergence caused by the focusing. Next, microfocusing was achieved by a bent multilayer arranged behind the crystal monochromator and alternatively by a bent Laue crystal. A 1.2 micro m-high line focus was obtained at 90 keV. The properties of the different set-ups are described and potential applications are discussed. First experiments were performed, investigating with high spatial resolution the residual strain gradients in layered polycrystalline materials. The results underline that focused high-energy synchrotron radiation can provide unique information on the mesoscopic scale to the materials scientist, complementary to existing techniques based on conventional X-ray sources, neutron scattering or electron microscopy.