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A geometrical-optical approach to the problem of the propagation of X-rays in weakly deformed crystals is developed in a general form along the lines of the Hamilton-Jakobi theory. It starts from the eikonal equation, which has been derived from Maxwell’s equations in Part I 1  and arrives at the equations of Penning and Polder 3  and Fermat’s principle by Kato  4 . The amplitude equation, which has also been derived in Part I, is interpreted by means of the energy-flow picture, the absorption being taken into account.

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Dynamische Theorie der Röntgenstrahl-Interferenzen an schwach verzerrten Kristallgittern: II. Strahlenoptik von BLOCH-Wellen im allgemeinen Fall und im Zweistrahlfall