Propagation of X-ray beams in distorted crystals (Bragg case). 2

The creation of new wavefields in deformed crystals, a phenomenon widely recognized as responsible for some contrast features in X-ray topography, has been demonstrated analytically for the first time only very recently in the case of a constant strain gradient. In the present paper it is shown by means of computer experiments (i.e. by solving Takagi's equations numerically) that the most important results of the theoretical approach can be readily extended to variable strain gradients. In particular, the conjecture is verified that the creation takes place only in the region of maximum curvature of the wavefield trajectory. Its relative intensity is shown to be equal to exp (-2π/mod(α0), α0 being proportional to the value of the strain gradient in that region. The utility of these results is demonstrated in a refined interpretation of the dislocation contrast in plane-wave reflection topography. (Auth.)