Qin Zeping, Xu Zijian, Li Ruoru, Liu Haigang, Liu Shilei, Wen Qingcao, Chen Xing, Zhang Xiangzhi, Tai Renzhong
Appl Opt. 2023 May 10;62(14):3542-3550. doi: 10.1364/AO.487694.
X-ray ptychography is a popular variant of coherent diffraction imaging that offers ultrahigh resolution for extended samples. In x-ray ptychography instruments, the Fresnel zone-plate (FZP) is the most commonly used optical probe system for both soft x-ray and hard x-ray. In FZP-based ptychography with a highly curved defocus probe wavefront, the reconstructed image quality can be significantly impacted by the initial probe function form, necessitating the construction of a suitable initial probe for successful reconstruction. To investigate the effects of initial probe forms on FZP-based ptychography reconstruction, we constructed four single-mode initial probe models (IPMs) and three multi-mode IPMs in this study, and systematically compared their corresponding simulated and experimental reconstructions. The results show that the Fresnel IPM, spherical IPM, and Fresnel-based multi-mode IPMs can result in successful reconstructions for both near-focus and defocus cases, while random IPMs and constant IPMs work only for near-focus cases. Consequently, for FZP-based ptychography, the elaborately constructed IPMs that closely resemble real probes in wavefront phase form are more advantageous than natural IPMs such as the random or constant model. Furthermore, these IPMs with high phase similarity to the high-curvature large-sized probe adopted in experiments can help greatly improve ptychography experiment efficiency and decrease radiation damage to samples.
X射线叠层成像术是相干衍射成像的一种流行变体，可为扩展样本提供超高分辨率。在X射线叠层成像仪器中，菲涅耳波带片（FZP）是软X射线和硬X射线最常用的光学探针系统。在基于FZP的叠层成像术中，使用高度弯曲的离焦探测波前时，重建图像质量会受到初始探针函数形式的显著影响，因此需要构建合适的初始探针以成功重建。为了研究初始探针形式对基于FZP的叠层成像术重建的影响，我们在本研究中构建了四个单模初始探针模型（IPM）和三个多模IPM，并系统地比较了它们相应的模拟和实验重建结果。结果表明，菲涅耳IPM、球面IPM和基于菲涅耳的多模IPM在近焦和离焦情况下都能成功重建，而随机IPM和常数IPM仅适用于近焦情况。因此，对于基于FZP的叠层成像术，精心构建的在波前相位形式上与真实探针非常相似的IPM比随机或常数模型等自然IPM更具优势。此外，这些与实验中采用的高曲率大尺寸探针具有高相位相似性的IPM有助于大大提高叠层成像术实验效率，并减少对样品的辐射损伤。
