Dispersive spread of virtual sources by asymmetricX-ray monochromators

• Published in: Journal of applied crystallography Vol. 45; no. 2
• Main Authors: Huang X. R., Cai Y., Macrander, A.T., Honnicke, M.G., Fernandez, P.
• Format: Journal Article
• Language: English
• Published: United States 26-01-2012
• Subjects: BRAGG REFLECTION; FOCUSING; MATERIALS SCIENCE; MONOCHROMATORS; national synchrotron light source; OPTICS; RECOMMENDATIONS; SCATTERING; SPECTROSCOPY; SYNCHROTRONS
• ISSN: 0021-8898; 1600-5767
• DOI: 10.1107/S0021889812003366

The principles of the virtual source spread (spatial broadening) phenomenon induced by angular dispersion in asymmetric X-ray Bragg reflections are illustrated, from which the virtual source properties are analyzed for typical high-resolution multiple-crystal monochromators, including inline four-bounce dispersive monochromators, back-reflection-dispersion monochromators and nondispersive nested channel-cut monochromators. It is found that dispersive monochromators can produce spread virtual sources of a few millimetres in size, which may prevent efficient microfocusing of the beam as required by inelastic X-ray scattering spectroscopy and other applications. Possible schemes to mitigate this problem are discussed. The analyses may provide important guidelines for designing and optimizing modern high-precision synchrotron X-ray optics and beamline instrumentation for spectroscopy, imaging and nanofocusing applications.