Forbidden X-ray wavefields of three-beam Bragg reflections from thick crystals.
A detailed analysis of a three-beam diffraction dispersion surface is performed to study the forbidden wavefields of thick-crystal Bragg reflections. From the asymptotic transition between two- and three-beam diffraction, it is found that the excitation state of each wavefield can be accurately determined with the two-beam criterion. Consequently, Bragg-case three-beam diffraction from thick crystals is either a four-mode diffraction process for the Bragg-Laue geometry or a two-mode process for the Bragg-Bragg geometry, and the amplitudes of the excited wavefields can be completely determined by the entrance boundary conditions. Based on this picture, the intrinsic mechanisms underlying three-beam Bragg reflections are clearly illustrated.
Huang
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Department of Materials Science and Engineering, State University of New York at Stony Brook, Stony Brook, New York 11794, USA. xiahuang@ms.cc.sunysb.edu
Dudley
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Zhao
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