Andreas Schropp

X-ray absorption near-edge structure (XANES) spectroscopy is key to understanding functional materials. We present, to our knowledge, the first use of hard x-ray near-field holography (NFH) for three-dimensional (3D), spatially resolved XANES. While NFH provides lensless imaging with an adjustable field of view, it entails complex reconstruction. Our method jointly reconstructs NFH data acquired at multiple energies and enforces a low-dimensional spectral model based on the physically motivated assumption that each voxel spectrum is a linear combination of a small number of constituents. We demonstrate the approach on a mixed metal oxide catalyst particle, achieving accurate spectral reconstruction and revealing 3D chemical heterogeneity. XANES in NFH mode has the potential to enable nano-scale in-operando XANES microscopy with a large field of view.

Ultrafast, high-power lasers operating in the near-infrared (NIR) region are key to accelerating ions to extremely high energies. By changing the laser wavelength from the NIR region to the hard X-ray range, the photon energy increases more than 10 000 times. The interaction mechanisms and, consequently, radiation attenuation lengths differ significantly between these two spectral ranges. Here we report the use of an X-ray free-electron laser (European XFEL, Germany) delivering 9.3 keV photons in 25 fs pulses and a total energy of 0.35 mJ on a solid target. Electrons and ions escaping from an irradiated 3 μm Cu foil into vacuum were investigated by a time-of-flight technique using windowless electron multipliers that enable the measurement of very weak currents. A model based on a shifted Maxwell–Boltzmann velocity distribution of species was used to analyze the detector signals. The method used made it possible to determine the temperatures of hot electrons and protons, their center-of-mass energy, the charge states of the isotopes 63Cu and 65Cu, and the magnitude of the voltage arising in the double layer that accelerated them, and to estimate the repetition frequency of their cascade emission from the plasma. Computer simulations revealed the evolution of the electron density and temperature, the ion charge state distribution, and the time scales of processes occurring in the bulk of irradiated matter. Good correlation of theoretical and experimental results over the range of high-energy-density states demonstrates the capability to provide critical data to develop plasma models in the warm dense matter regime.

Hundreds of cuneiform clay tablets unearthed in South-western Asia remain sealed within clay envelopes, leaving their texts inaccessible to Assyriologists. Computed tomography (CT) enables looking inside the clay envelopes non-destructively. An interdisciplinary team developed a transportable high-definition CT scanner named by ENCI, designed for on-site use in museums and archives. ENCI allows researchers to visualise the cuneiform text written on hidden tablets, study clay inclusions, and analyse manufacturing techniques without opening the tablets. First deployed at the Louvre Museum in Paris in 2024, it was later used at the Museum of Anatolian Civilisations in Ankara to scan around fifty encased tablets, many of them letters. Combined with advanced 3D surface extraction and visualisation software, ENCI enables virtual unwrapping and detailed exploration of small objects. This technology opens new possibilities for studying cultural heritage artefacts on site, while also revealing mineral and organic inclusions and evidence of envelope formation methods.

This study demonstrates a non-destructive approach to investigating the structure of bookbindings in historical manuscripts using high-resolution X-ray computed tomography (CT). We applied the portable CT scanner ENCI to a Georgian codex from the Graz University Library, MS 2058/1, the famous Sinai Lectionary. Three-dimensional reconstructions reveal the complex arrangement of the spine, cords, threads, and gatherings of folios. Individual characters written in vermilion and iron gall ink can be digitally segmented and distinguished. These results highlight the potential of X-ray tomography as a powerful, non-invasive tool for the structural and textual analysis of delicate manuscripts, offering new opportunities to study fragile or partially damaged books while preserving their physical integrity.

Hard X-ray ptychography has strongly developed during the last decade, enabling one to visualize structural properties of materials at high spatial resolution. By combining it with multi-slicing or tomographic techniques, optically thick samples can be investigated in 3D. Nevertheless, the depth resolution in multi-slicing is often limited to several micrometers by the ptychographic optical system and a full laminographic or tomographic investigation may be hindered by experimental constraints of limited space or acquisition time. Here, we introduce a stereoscopic imaging system using two inclined nanofocused X-ray beams to illuminate a sample at varying angles at the same time. Similar to human vision, adding these stereoscopic views results in considerably improved in-depth resolution beyond the current limits of pure 2D imaging systems. This is especially promising for experimental applications requiring bulky sample environments.

Au bipyramids hosting body-centered orthorhombic and tetragonal lattices (bc(o,t)) exhibit extraordinary stability at ambient conditions and even under high-temperature/high-pressure conditions. The phases undergo conversion to a conventional face-centered cubic (fcc) lattice only during annealing at 700 °C due to the unlocking of the geometrically induced stresses. The spatial distribution of the phases in the crystallite volume has revealed fcc capped bc(o,t) lattices with two halves of the bipyramid twisted by ∼6° along the length with approximately ± 5% strain. Understanding the spatial distribution and dynamics of these phases at high temperatures can provide detailed information on their thermal stability. Herein, using nanoprobe scanning X-ray diffraction microscopy (SXDM), in situ annealing of the bc(o,t) Au bipyramid (∼1.5 μm long and 300 nm wide) has been performed at different temperatures (up to 800 °C). The study reveals untwisting of the domains assisted by the supplied high temperature, while the existing lattices undergo variation in parameters with negligible changes in proportion. The study reveals and picturizes the dynamic change in diffracting volumes across a wide temperature range. Notably, despite annealing, ∼83% of the bc(o,t) content is still retained (with different lattice parameters), proposing the annealing route to produce unusual metastable lattices of gold.

An erratum is presented to correct the stated numerical aperture of the employed multilayer Laue lenses in our previously published paper [ Opt. Express 30, 31519 (2022)10.1364/OE.454863 ].

We demonstrate live-updating ptychographic reconstruction with the extended ptychographical iterative engine, an iterative ptychography method, during ongoing data acquisition. The reconstruction starts with a small subset of the total data, and as the acquisition proceeds the data used for reconstruction are extended. This creates a live-updating view of object and illumination that allows monitoring the ongoing experiment and adjusting parameters with quick turn around. This is particularly advantageous for long-running acquisitions. We show that such a gradual reconstruction yields interpretable results already with a small subset of the data. We show simulated live processing with various scan patterns, parallelized reconstruction, and real-world live processing at the hard X-ray ptychographic nanoanalytical microscope PtyNAMi at the PETRA III beamline.

We demonstrate live-updating ptychographic reconstruction with ePIE, an iterative ptychography method, during ongoing data acquisition. The reconstruction starts with a small subset of the total data, and as the acquisition proceeds the data used for reconstruction is extended. This creates a live-updating view of object and illumination that allows monitoring the ongoing experiment and adjusting parameters with quick turn-around. This is particularly advantageous for long-running acquisitions. We show that such a gradual reconstruction yields interpretable results already with a small subset of the data. We show simulated live processing with various scan patterns, parallelized reconstruction, and real-world live processing at the hard X-ray ptychographic nanoanalytical microscope PtyNAMi at the PETRA III beamline.