X-ray topography of bent crystals

The influence of the bending of a crystal on the formation of diffracted images in Bragg section topographs as well as in Laue section and traverse topographs is studied. In the case of Bragg section topography the interferometric fringes due to the interference of waves once and twice internally reflected inside a bent crystal are described. It is established that the maximum positions of diffracted intensity satisfy the law x_n = [16π(2n - 1)/5B²]^1/3, where x_n is the distance from the incidence slit of the X-rays, B is the uniform strain gradient and n is the fringe number. This dependence is found to be in good agreement with experimental data. The Laue section topograph of a bent crystal with a screw dislocation parallel to the diffraction vector is considered. The effects of asymmetry in the Pendellösung fringe pattern and of 'splitting' of the direct image with respect to the dislocation line in both the experimental and simulated topographs are accounted for. The variation of the contrast of dislocations with depth inside a bent crystal in Laue traverse topographs is studied by computer simulations using the reciprocity theorem.