Effect of finite spatial coherence length on small-angle scattering

This study shows that forward scattering at the origin of reciprocal space contributes to the scattering intensity profiles of ultra-small-angle scattering. The forward scattering corresponds to a Fourier transform of the X-ray coherent volume on a sample. This contribution is usually ignored in the study of small-angle scattering, while it is fully considered in the fields of X-ray imaging, such as coherent X-ray diffraction imaging and X-ray ptychography. This effect is explicitly illustrated in the context of small-angle scattering, and the effect of a finite spatial coherence length on small-angle scattering is discussed.