Abstract
Ptychographic X-ray computed tomography is a coherent diffractive imaging method that offers nanometer-scale resolution with quantitative contrast. It offers the possibility to study relatively thick samples by using high energy X-ray photons and exploiting the phase contrast. However, the limited depth of field forces a compromise between resolution and sample thickness. Multi-slice techniques have been used to account for propagation effects within the sample, enabling imaging beyond the depth-of-field limit. Here we introduce and experimentally demonstrate our multi-slice algorithms that allow for the reconstruction of multiple object slices and the incident illumination, as well as the retrieval of unknown object thickness. Additionally, through numerical studies, we show that smaller scanning steps surprisingly increase the depth of field, which can be further extended by the use of multi-slice methods under conditions stated by theoretical expressions. The results presented here will be instrumental for the routine implementation of the technique for X-ray nanotomography.
Highlights
The depth of field (DOF) refers to the distance by which a sample can be translated in the direction of beam propagation while remaining in the focus of an imaging system
To extend the DOF, focus stacking has been used in photography and optical microscopy by merging images taken at different focus through image processing techniques [1]
The DOF limit arises in ptychography due to the assumption that the exit X-ray wavefield can be expressed as the product of a 2D object and the incident illumination, given by ψ j,r = Pr−rj Or, (1)
Summary
The depth of field (DOF) refers to the distance by which a sample can be translated in the direction of beam propagation while remaining in the focus of an imaging system It limits the regions within which high-resolution diffraction-limited imaging can be achieved. The DOF limitation can be lifted by incorporating the simultaneous reconstruction of multiple axial slices of the object along the propagation direction In this manner, a ptychographic reconstruction algorithm addresses propagation effects including multiple scattering and diffraction within the sample. A ptychographic reconstruction algorithm addresses propagation effects including multiple scattering and diffraction within the sample This multi-slice solution enables ptychographic imaging beyond the DOF limit using a conventional 2D ptychography data set. We further quantify the benefits gained by multi-slice reconstructions, giving insight into when and how the method should be applied
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