Measurements of an Effective Longitudinal Coherence Length in Transmission Small Angle X-ray Scatterings

The notion of an effective longitudinal coherence length with its value much greater than [Formula: see text] has been adopted in small-angle X-ray scattering communities for years, where [Formula: see text] and [Formula: see text] denote the incident wavelength and its spread, respectively. Often the implications of the effective longitudinal coherence length do not even enter considerations in the designing and data treatment of small-angle scattering experiments. In this work, conventional transmission small-angle X-ray scattering (tSAXS) was performed to reveal a clear angular dependence on effective longitudinal coherence length. The measured values of effective longitudinal coherence length can be as high as one millimeter, whereas the value of calculated [Formula: see text] is in nanometers.