X-ray diffraction pictures for Fourier-transformed narrow incident beams

Influence of the Fourier transform of the incident beam on the measured diffracted intensity in X-ray diffraction is analysed. The theory presented is a more rigorous physical picture of X-ray diffraction in the case of a narrow incident beam than the usually assumed spherical-wave theory. The shape of diffracted beam amplitude depends on the FT of the incident beam which is fully determined by experimental conditions. The proposed methods may be used for direct calculations of the correlation function for electromagnetic fields and studies of the coherence degree of X-ray radiation.