Comparison between X-ray imaging by Fresnel zone plate and projection-type phase contrast imaging by numerical simulations

X-ray diffraction imaging is capable of realizing near-diffraction-limited spatial resolution. This paper uses analytical and numerical approaches to study and compare Fresnel zone plate (FZP) imaging and projection-type phase contrast imaging of an object backlit by an X-ray source. The energy of X-rays is the Ti K line (4.5 keV) or Cu K line (8 keV). The results show that the spatial resolution of FZP imaging is better than 1 m, and it is beneficial to use a backlighting source of larger size. For high transmission or weak absorption object, FZP imaging does not work well due to poor contrast. In this case, projection-type phase contrast imaging may be applied to achieve a spatial resolution of a few microns. By including higher-order effect that was not considered before, analytical formulae for image intensity and contrast are given. Numerical approaches are also used to study the phase contrast imaging of thin film target with thickness fluctuations or spatial density modulations illuminated by a microfocus X-ray source. In the case of a point source the theoretical contrast of images coincides well with simulation result. The influence of X-ray source size and imaging distance on the images contrast and spatial resolution is discussed. It is indicated that by controlling the source size and changing the distance between the object and the detector, the spatial resolution could be optimized to 1-4 m.