Published online by Cambridge University Press: 06 March 2019
Complete dynamical solutions for three coupled plane-wave components in crystal structures with inversion symmetry have been found. After reviewing briefly the dynamical solutions for wave fields with two coupled plane-wave components, the results for the three-beam case are discussed in qualitative terms. Attention is paid to singular points and lines on the ω-surface, and to the attenuation of the mode-intensity because of absorption. The most surprising result is that in the case one of the reflections is forbidden (Umweganregung) the absorption is reduced in comparison with the adjoining two-beam cases. Experimental data are in reasonable agreement with the theory. Quantitative data are presented for a few three-beam cases of simultaneous diffraction of Cu Kα. radiation in germanium.