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Physical review letters 130(17), 173201 (2023). doi:10.1103/PhysRevLett.130.173201, We demonstrate that x-ray fluorescence emission, which cannot maintain a stationary interference pattern, can be used to obtain images of structures by recording photon-photon correlations in the manner of the stellar intensity interferometry of Hanbury Brown and Twiss. This is achieved utilizing femtosecond-duration pulses of a hard x-ray free-electron laser to generate the emission in exposures comparable to the coherence time of the fluorescence. Iterative phasing of the photon correlation map generated a model-free real-space image of the structure of the emitters. Since fluorescence can dominate coherent scattering, this may enable imaging uncrystallised macromolecules., Published by APS, College Park, Md.

Hanbury Brown and Twiss interferometry experiment based on second-order correlations was performed at PAL-XFEL facility. The statistical properties of the X-ray radiation were studied within this experiment. Measurements were performed at NCI beamline at 10 keV photon energy in various operation conditions: Self-Amplified Spontaneous Emission (SASE), SASE with a monochromator, and self-seeding regimes at 120 pC, 180 pC, and 200 pC electron bunch charge, respectively. Statistical analysis showed short average pulse duration from 6 fs to 9 fs depending on operation conditions. A high spatial degree of coherence of about 70-80% was determined in spatial domain for the SASE beams with the monochromator and self-seeding regime of operation. The obtained values describe the statistical properties of the beams generated at PAL-XFEL facility., 30 pages, 10 figures, 2 tables

Optics express 30(14), 25450 - (2022). doi:10.1364/OE.460903, In recent years, X-ray speckle tracking techniques have emerged as viable tools for wavefront metrology and sample imaging applications, and have been actively developed for use at synchrotron light sources. Speckle techniques can recover an image free of aberrations and can be used to measure wavefronts with a high angular sensitivity. Since they are compatible with low-coherence sources they can be also used with laboratory X-ray sources. A new implementation of the ptychographic X-ray speckle tracking method, suitable for the metrology of highly divergent wavefields, such as those created by multilayer Laue lenses, is presented here. This new program incorporates machine learning techniques such as Huber and non-parametric regression and enables robust and quick wavefield measurements and data evaluation even for low brilliance X-ray beams, and the imaging of low-contrast samples. To realize this, a software suite was written in Python 3, with a C back-end capable of concurrent calculations for high performance. It is accessible as a Python module and is available as source code under Version 3 or later of the GNU General Public License., Published by Soc., Washington, DC

Nature Communications 13(1), 892 (2022). doi:10.1038/s41467-022-28486-3, We correlate spatially resolved fluorescence (-lifetime) measurements with X-ray nanodiffractionto reveal surface defects in supercrystals of self-assembled cesium lead halideperovskite nanocrystals and study their effect on the fluorescence properties. Upon comparisonwith density functional modeling, we show that a loss in structural coherence, anincreasing atomic misalignment between adjacent nanocrystals, and growing compressivestrain near the surface of the supercrystal are responsible for the observed fluorescenceblueshift and decreased fluorescence lifetimes. Such surface defect-related optical propertiesextend the frequently assumed analogy between atoms and nanocrystals as so-called quasiatoms.Our results emphasize the importance of minimizing strain during the self-assemblyof perovskite nanocrystals into supercrystals for lighting application such as superfluorescentemitters., Published by Nature Publishing Group UK, [London]

Science advances 7(40), eabh0757 (2021). doi:10.1126/sciadv.abh0757, The imaging of active nanoparticles represents a milestone in decoding heterogeneous catalysts’ dynamics. We report the facet-resolved, surface strain state of a single PtRh alloy nanoparticle on SrTiO$_3$ determined by coherent x-ray diffraction imaging under catalytic reaction conditions. Density functional theory calculations allow us to correlate the facet surface strain state to its reaction environment–dependent chemical composition. We find that the initially Pt-terminated nanoparticle surface gets Rh-enriched under CO oxidation reaction conditions. The local composition is facet orientation dependent, and the Rh enrichment is nonreversible under subsequent CO reduction. Tracking facet-resolved strain and composition under operando conditions is crucial for a rational design of more efficient heterogeneous catalysts with tailored activity, selectivity, and lifetime., Published by Assoc., Washington, DC [u.a.]

Nanoscale 13(25), 11299 - 11300 (2021). doi:10.1039/D1NR90126E, Correction for ���Exploring the 3D structure and defects of a self-assembled gold mesocrystal by coherent X-ray diffraction imaging��� by Jerome Carnis et al., Nanoscale, 2021, DOI: 10.1039/D1NR01806J., Published by RSC Publ., Cambridge

Structural dynamics 8(4), 044305 (2021). doi:10.1063/4.0000127, Second-order intensity interferometry was employed to study the spatial and temporal properties of the European X-ray Free-Electron Laser(EuXFEL). Measurements were performed at the soft x-ray Self-Amplified Spontaneous Emission (SASE3) undulator beamline at a photonenergy of 1.2 keV in the Self-Amplified Spontaneous Emission (SASE) mode. Two high-power regimes of the SASE3 undulator settings, i.e.,linear and quadratic undulator tapering at saturation, were studied in detail and compared with the linear gain regime. The statistical analysisshowed an exceptionally high degree of spatial coherence up to 90% for the linear undulator tapering. Analysis of the measured data in spectraland spatial domains provided an average pulse duration of about 10 fs in our measurements. The obtained results will be valuable for theexperiments requiring and exploiting short pulse duration and utilizing high coherence properties of the EuXFEL., Published by AIP Publishing LLC, Melville, NY