XRM2024 - Thu03K - "Adaptive multi-beam ptychography"

X-ray ptychography is a powerful imaging technique available at synchrotron facilities, offering high resolution images at the nanoscale. Efforts are underway to make this technique more efficient, especially in obtaining data for larger areas more quickly. Multi-beam ptychography, which involves using multiple beams simultaneously, is a promising method. Previous work in the field has made use of adjacent optical components, resulting in rather large beam spacings, or of a split secondary source, resulting in small beam spacings. These spacings have so far always been fixed. We here present a novel approach to multi-beam ptychography. Specifically, we create separate and adaptively spaced beams by using stacked Fresnel zone plates (FZPs), which allow us to work in either of the mentioned beam spacing regimes, and in between, with the same setup. 

There are different modalities that our setup can be used for. By stacking the FZPs conventionally, we can generate a single, strong probe for detailed imaging in a small area. Alternatively, by separating the FZPs, we can create multiple probes. These probes can be as close as a few microns apart, and multi-beam ptychography becomes applicable to both larger and smaller samples. 

Our method relies on FZPs designed with specific zones being inverted. This “coding” of the FZPs facilitates separation of different probes during the image reconstruction process. Additionally, the FZPs have matched numerical apertures, granted by marginally different diameters, and produce beams that are comparable in size. Therefore, these beams illuminate the sample in a comparable way, and the step size that is chosen for scanning will satisfy the sampling criteria for both at the same time. 

We call our approach adaptive multi-beam ptychography because it allows us to adjust the illumination conditions according to our needs in each experiment, such as the size of the sample and how the detector captures data. 

References:
[1] Mattias Åstrand et al., "Adaptive multi-beam X-ray ptychography", Opt. Express 32, 22771-22780 (2024) https://doi.org/10.1364/OE.509813
[2] Mattias Åstrand et al., "Multi-beam multi-slice X-ray ptychography", Sci Rep 15, 9273 (2025). https://doi.org/10.1038/s41598-025-93757-0
[3] Mattias Åstrand, PhD thesis: "X-ray ptychography with multiple beams", (2025) https://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-360505