Non‐projectiveness of X‐ray Pendellösung‐fringed diffraction images

It has been experimentally found that X‐ray moiré fringes are not exactly given as a projected figure from the specimen crystal as predicted by the standard theory of X‐ray dynamical diffraction, but show a kind of spatial oscillation along the beam path out of the crystal. This paper reports that a similar spatial oscillation has been found for Pendellösung fringes in a similar experiment recording plane‐wave X‐ray topographs of a silicon wedge crystal onto a set of multi‐stacked films. The oscillation of the Pendellösung fringes was easily found among the simultaneous topographs on the multi‐stacked films by examining the fringe profiles, and was also found in topographic images by somewhat careful inspection. It is noteworthy that a simple reciprocal correspondence was observed between the amplitude of fringe oscillation and the fringe contrast. This finding of non‐projectiveness, i.e. the fringe oscillation noted above, in Pendellösung fringes as well as in moiré fringes suggests that the non‐projectiveness occurs as a very basic property of X‐ray interference fringes produced by crystal diffraction.