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The first experimental demonstration of saturable absorption in core-electron transitions in aluminium paves the way for investigating warm dense matter, which potentially has an important role in planetary science and the realization of inertial confinement fusion.

The main protease, a key enzyme of SARS-CoV-2, can protect itself from oxidative damage. Here, Reinke, Schubert, and colleagues used XFEL radiation to image the enzyme, revealing the disulfide and NOS/SONOS bonds that form in response to oxygen.

Dendritic cells are supplied antigens by other cells such as lymphatic endothelial cells (LEC) at late time points after immunization. Here the authors show antigen archiving is defined by a transcriptional program that can predict antigen archiving depending on the priming pathogen, and that boosting of immune responses increases the archiving.

Intense, coherent X-ray pulses from a free-electron laser can be used to obtain high-resolution morphology of individual sub-micrometre particles in their native state, while at the same time their composition is analysed by mass spectrometry.

The European X-ray free-electron laser (EuXFEL) in Hamburg is the first XFEL with a megahertz repetition rate. Here the authors present the 2.9 Å structure of the large membrane protein complex Photosystem I from T. elongatus that was determined at the EuXFEL.

A modern version of Newton's 'dusty 'mirror' experiment is made, whereby X-ray pulses are focused on a thin membrane with polystyrene particles placed in front of an X-ray mirror. After a pulse traverses through the sample, triggering the explosion of a particle, it is reflected back on to the sample by the mirror to probe this reaction. The resulting diffraction pattern contains accurate time and spatially resolved information about the exploding particles.

Researchers describe a mechanism capable of compressing fast and intense X-ray pulses through the rapid loss of crystalline periodicity. It is hoped that this concept, combined with X-ray free-electron laser technology, will allow scientists to obtain structural information at atomic resolutions.

Lipidic sponge phase crystallization yields membrane protein microcrystals that can be injected into an X-ray free electron laser beam, yielding diffraction patterns that can be processed to recover the crystal structure.

Free-electron lasers enable diffractive imaging of single nanostructures, but algorithms, such as correlation analyses, are needed to determine their diffraction volume from accumulated data. Starodub et al.present such a method for X-ray diffractive imaging of nanometre-scale polystyrene dimers.

The electrical conductivity is critical to understand warm dense matter, but the accurate measurement is extremely challenging. Here the authors use multi-cycle THz pulses to measure the conductivity of gold foils strongly heated by free-electron laser, determining the individual contributions of electron-electron and electron-ion scattering.

The start-up of the new femtosecond hard X-ray laser facility in Stanford, the Linac Coherent Light Source, has brought high expectations for a new era for biological imaging. The intense, ultrashort X-ray pulses allow diffraction imaging of small structures before radiation damage occurs. This new capability is tested for the problem of imaging a non-crystalline biological sample. Images of mimivirus are obtained, the largest known virus with a total diameter of about 0.75 micrometres, by injecting a beam of cooled mimivirus particles into the X-ray beam. The measurements indicate no damage during imaging and prove the concept of this imaging technique.

The start-up of the new femtosecond hard X-ray laser facility in Stanford, the Linac Coherent Light Source, has brought high expectations for a new era for biological imaging. The intense, ultrashort X-ray pulses allow diffraction imaging of small structures before radiation damage occurs. This new capability is tested for the problem of structure determination from nanocrystals of macromolecules that cannot be grown in large crystals. Over three million diffraction patterns were collected from a stream of nanocrystals of the membrane protein complex photosystem I, which allowed the assembly of a three-dimensional data set for this protein, and proves the concept of this imaging technique.

The new European X-Ray Free-Electron Laser (EuXFEL) is the first XFEL that generates X-ray pulses with a megahertz inter-pulse spacing. Here the authors demonstrate that high-quality and damage-free protein structures can be obtained with the currently available 1.1 MHz repetition rate pulses using lysozyme as a test case and furthermore present a β-lactamase structure.

Expression of a protein in Sf9 insect cells at high concentration triggers formation of in vivo crystals that can be analyzed by serial femtosecond X-ray crystallography.