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Figure 2
Dispersion surface in a Bragg geometry. La is the Laue point, Lo the Lorentz point and c1 the tie point for Ws = −1. The solid line [T_0'] represents the dispersion surface in a vacuum for an incident beam of energy E and the solid curve the corresponding dispersion surface of branches (1) and (2) in the crystal. The dot–dashed curve T0 represents the asymptote of the dispersion surface in the crystal. The dashed line represents the dispersion surface in a vacuum for an X-ray of energy [E - \delta E]. The angle change [\delta \alpha] gives the same change in [\delta W{X_0}] as the change in the wavevector [\delta {{\bf{K}}_E}] gives when the energy changes from E to [E - \delta E]. The relations [|{{\bf{K}}_0}({\alpha _0})| = |{{\bf{K}}_0}({\alpha _0} - \delta \alpha)|] and [| {{{\bf{K}}_0}({\theta _{\rm{B}}})} | =] [| {{\bf{K}}_0'({\theta _{\rm{B}}} + \delta {\theta _{\rm{B}}})} | +] [| {\delta {{\bf{K}}_E}} |] hold.

Journal logoJOURNAL OF
APPLIED
CRYSTALLOGRAPHY
ISSN: 1600-5767
Volume 47| Part 4| August 2014| Pages 1267-1272
https://doi.org/10.1107/S1600576714012114
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