Initial probe function construction in ptychography based on zone-plate optics.

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.