The role of the non‐monochromaticity of the radiation as well as of the source dimensions is analyzed in the X‐ray section topography of single crystals. It is shown that for usual experimental conditions when the film is placed directly behind the crystal, the slit in front of the crystal really plays the part of an incoherent source, and the distance between the real source and the crystal has no affect on the interference pattern. A new type of interference pattern is revealed experimentally while changing the slit dimensions. The experimental results agree with theoretical computations.
The general theory of X-ray spherical-wave diffraction in two, either identical or different in nature, spatially separated perfect crystals is developed. The theory takes into account the phase shift of the waves both inside the crystals and in vacuum before, between and after the crystals. The nonmonochromaticity of radiation, the source dimension and the placing of a slit before the first crystal are considered. The results of theoretical calculation and an experimental study of the interference fringes and focusing the radiation are presented. A good agreement between the experimental and theoretical data is obtained for values of the experimental parameters that affect focusing.
The mechanism of formation of X‐ray diffraction images of straight line dislocations in section topographs has been investigated. The image character for dislocations in the special position fully results from the diffraction power of a dislocation m = (KHb)2π. The analysis of the extinction fringes map corresponding to dislocation distorted slit image suggests the possibility of the interferometric investigation of the elastic stress field. The number of additional fringes corresponds to a dislocation‐induced maximum phase shift and amounts to approximately 0.4m. The direct image formation is related to focusing of additional wave field generated in the dislocation short‐range field over the whole width of the Borman fan. Fine structure of the direct image yields, under certain conditions, information on the dislocation elastic field. A part of the interferometric information on a dislocation remains valid in transformation from section topographs to those traverse.
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