Interference fringes in multiple Bragg-Laue mode

Interference fringes in multiple Bragg-Laue mode have been measured from the lateral surface of an Si plane-parallel crystal by changing the distance L between the incident point of X-rays and the crystal edge for two sample crystals with different thicknesses H. The period of the interference fringes becomes large when the distance L becomes large or the thickness H becomes small. When the ratio L/H is larger than 15, a shorter period of oscillation appears in addition to the interference fringes. These variations are explained by considering the beams in multiple Bragg-Laue modes based on the dynamical theory of diffraction. When L/H is less than 15, the measured fringes are well reproduced by taking account of interference between beams in the Bragg-Laue and the Bragg-Bragg-Laue modes. The short period of the oscillations observed for L/H > 15 is reproduced by adding the intensities of the beams in higher-order Bragg-Laue mode. The interference fringes calculated by taking the visibility into account show good agreement with the measured ones.