Halo and dark zones at capsule shell interface in X-ray phase contrast imaging

X-ray phase contrast imaging experiments have been performed on micro-focus X-ray facility and Shenguang-Ⅱ laser driven plasma X-ray source. The Halo and dark zones at capsule shell interface have been found. Our work proposed the principle of light refraction to explain the halo and dark zones, and acquires the theoretic width of the halo and dark zones by sphere model and geometry optics. The theoretic width accords well with the experimental results. Thus, phase contrast imaging has an advantage over absorption imaging in low-Z material sample, and the halo and dark zones are very useful for precise diagnoses in low-Z material interface.