Effects of dispersion and absorption in resonant Bragg diffraction of x-rays

DOI: 10.1088/0953-8984/26/12/125504
PMID: 24599265

Authors: S. W. Lovesey (Diamond Light Source) , V. Scagnoli (Paul Scherrer Institut) , A. N. Dobrynin (Diamond Light Source) , Y. Joly (Institut Néel, CNRS and Université Joseph Fourier,) , S. P. Collins (Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Physics: Condensed Matter , VOL 26 (12) , PAGES 332-337

State: Published (Approved)
Published: March 2014

Abstract: Resonant diffraction of x-rays by crystals with anisotropic optical properties is investigated theoretically, to assess how the intensity of a Bragg spot is influenced by effects related to dispersion (birefringence) and absorption (dichroism). Starting from an exact but opaque expression, simple analytic results are found to expose how intensity depends on dispersion and absorption in the primary and secondary beams and, also, the azimuthal angle (rotation of the crystal about the Bragg wavevector). If not the full story for a given application, our results are more than adequate to explore consequences of dispersion and absorption in the intensity of a Bragg spot. Results are evaluated for antiferromagnetic copper oxide, and low quartz. For CuO, one of our results reproduces all salient features of a previously published simulation of the azimuthal-angle dependence of a magnetic Bragg peak. It is transparent in our analytic result that dispersion and absorption effects alone cannot reproduce published experimental data. Available data for the azimuthal-angle dependence of space-group forbidden reflections. (0, 0, l), with l not equal 3n, of low quartz depart from symmetry imposed by the triad axis of rotation symmetry. The observed asymmetry can be induced by dispersion and absorption even though absorption coefficients are constant, independent of the azimuthal angle, in this class of reflections.

Journal Keywords: Resonant Bragg Diffraction; Dispersion And Absorption; Copper Oxide; Quartz; Absorption; Anisotropy; Antiferromagnetism; Birefringence; Bragg Curve; Bragg Reflection; Copper Oxides; Crystals; Optical Properties; Quartz; Secondary Beams; Space Groups

Subject Areas: Physics, Materials


Technical Areas: Theoretical Physics