Advancing partially coherent diffraction imaging and near-field ptychography

Abstract:

Recent progress in short-wavelength sources has enabled coherent diffraction imaging (CDI) to probe matter at atomic and nanometer length scales, offering a powerful route for non-destructive imaging of complex functional materials. However, practical implementations withlaboratory-scale light sources remain constrained by available coherent flux to achieve their full potential. For example, ptychography with liquid metal-jet X-ray sources must balance photon flux against spatial and temporal coherence, while subangstrom electron ptychography typically relies on expensive aberration correctors and fast detectors to mitigate decoherence arising from optical imperfections and specimen instability. Similarly, stroboscopic CDI with high harmonic generation (HHG) sources is also limited by the low coherence of the illumination. On the one hand, the energy bandwidth and temporal pulse duration of femtosecond and attosecond pulses are strictly governed by the uncertainty principle, resulting in the broad bandwidth that may degrade phase retrieval quality. On the other hand, intensity-dependent phase distortions during generation degrade the inherent spatial coherence of HHG beams, dictating that these sources ultimately be modeled as partially spatially coherent.

In this talk, I will provide an overview of partially coherent CDI and present our contribution to the proof-of-concept simulation frameworks, optical setup design and forward diffraction model for polychromatic far-field diffraction. Building on this understanding, I will introduce our developed approaches for enhancing computational efficiency and robustness against extremely low coherence.

Beyond the constraints of coherence, the long acquisition time required for 3D X-ray ptychography presents a major practical challenge. Near-field ptychography has proven effective for scanning large volumes with a larger probe and fewer scan points compared to far-field ptychography, yet it faces an intrinsic resolution limit imposed by the detector pixel size.

Here, I will present our work on mitigating this limitation to enhance the spatial resolution of near-field ptychography. I will also show its application in X-ray ptychographic laminography for high-resolution brain imaging and outline specific method to optimize this approach for higher resolution.