title: Three-beam X-ray diffraction in a semi-infinite perfect crystal.
abstract: The approach to multibeam X-ray diffraction by Shen [Acta Cryst. (1986). A42, 525-533] has been carefully re-examined for three-beam Laue-Laue diffraction in a perfect non-absorbing semi-infinite crystal. A modified version of Shen's theory is shown to be equivalent to the Takagi-Taupin formalism. The perturbation of the two-beam integrated power when a third beam is being excited is thus expressed by non-diverging terms. Both Aufhellung and Umweganregung terms are recovered.
authors.affiliation: Department of Mathematics and Natural Science, Stavanger University College, Ullandhaug, N-4091 Stavanger, Norway. gunnar.thorkildsen@tn.his.no
authors.forename: Gunnar
authors.initials: G
authors.lastname: Thorkildsen
authors.forename: Helge B
authors.initials: HB
authors.lastname: Larsen