Study of extremely asymmetric X-ray diffraction in the Bragg case of grazing incidence

The deviation from the Bragg law and the incident half width wi of the diffraction pattern, which can be obtained by numerical and geometrical extension of the dynamical theory of X-ray diffraction, are compared together. An analytical expression for the emergent half width we is derived. It is shown, that we can be calculated according to the conventional theory from we = bwi (b is the asymmetry factor). The relation is valid also, when the incident geometrical Bragg position is in the range of specular reflection, but in this case b and wiconv are only fictive quantities.