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Interatomic Coulombic decay (ICD) is a relaxation of an atom in a weakly bound environment by the transfer of excess energy to ionize the neighbouring atom. Here the authors observe intra-Rydberg ICD in neon clusters, which is a decay that involves the ionization of Rydberg atoms in the cluster.

Self-referenced attosecond streaking enables in situ measurements of Auger emission in atomic neon excited by femtosecond pulses from an X-ray free-electron laser with subfemtosecond time resolution and despite the jitter inherent to X-ray free-electron lasers.

Two-color X-ray pulses with controlled time delay allow exciting one site of a molecule and then probing a different site of the same molecule with femtosecond resolution. Here, the authors use this hetero-site pump-probe technique to study charge redistribution and dissociation of the xenon difluoride molecule.

X-ray free electron lasers provide high photon flux to explore single particle diffraction imaging of biological samples. Here the authors present dynamic electronic structure calculations and benchmark them to single-particle XFEL diffraction data of sucrose clusters to predict optimal single-shot imaging conditions.

Understanding the dynamics of molecules exposed to intense X-ray beams is crucial to ongoing efforts in biomolecular imaging with free-electron lasers. Here, the authors study C₆₀molecules interacting with femtosecond X-ray free-electron laser pulses and present a model based on classical and quantum physics.

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.

Time-resolved measurements of the X-ray photoemission delay of core-level electrons using attosecond soft X-ray pulses from a free-electron laser can be used to determine the complex correlated dynamics of photoionization.

Two-colour X-ray pulses from free-electron lasers can be used to probe ultrafast dynamics, but the total power is a fraction of the saturation power. Here, Marinelli et al. use twin electron bunches to reach full saturation power and increase the two-colour intensity by an order of magnitude at hard-X-ray energies.

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.

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.

Photoexciting molecules provides insights into their different degrees of freedom if the ultrafast electron and nuclei motion can be properly analysed. To this end, McFarland et al.use X-ray pump-probe techniques to show that Auger spectra can unveil information on nuclear relaxation in molecules.

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.

Imaging live cells at nanometre resolution is challenging because radiation damage kills the cells during exposure. Here, the authors overcome this difficulty in a ‘diffraction before destruction’ experiment using an X-ray laser and record signal to 4 nm resolution on a free-flying cell.

Some X-ray free-electron laser facilities are pushing towards sub-10 fs pulses, making it desirable to reduce errors in X-ray/optical delay measurements to the 1 fs level. Researchers have now demonstrated X-ray measurements with a temporal resolution shorter than 1 fs, opening up new possibilities for time-resolved X-ray experiments.

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.

A femtosecond, high-intensity atomic X-ray laser with a photon energy of 849 electronvolts is produced in singly ionized neon by pumping using an X-ray free-electron laser.

Using a spectroscopy streaking technique at LCLS (Linac Coherent Light Source), researchers demonstrate temporal characterization of X-ray pulses with sub-femtosecond resolution.

Many photo-induced processes such as photosynthesis occur in organic molecules, but their femtosecond excited-state dynamics are difficult to track. Here, the authors exploit the element and site selectivity of soft X-ray absorption to sensitively follow the ultrafast ππ*/nπ* electronic relaxation of hetero-organic molecules.

X-ray free-electron lasers, important light sources for materials research, suffer from shot-to-shot fluctuations that necessitate complex diagnostics. Here, the authors apply machine learning to accurately predict pulse properties, using parameters that can be acquired at high-repetition rates.

With the start-up of the first X-ray free-electron laser, a new era has begun in dynamical studies of atoms. Here the facility is used to study the fundamental nature of the electronic response in free neon atoms. During a single X-ray pulse, they sequentially eject all their ten electrons to produce fully stripped neon. The authors explain this electron-stripping in a straightforward model, auguring favourably for further studies of interactions of X-rays with more complex systems.

70,000 diffraction patterns captured over twelve minutes at the Linac Coherent Light Source yield reconstructions of the smallest single biological objects imaged with an X-ray laser.

The Linac Coherent Light Source free-electron laser has now achieved coherent X-ray generation down to a wavelength of 1.2 Å and at a brightness that is nearly ten orders of magnitude higher than conventional synchrotrons. Researchers detail the first operation and beam characteristics of the system, which give hope for imaging at atomic spatial and temporal scales.

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.

Attosecond time–energy characterization of pulses generated by the Linac Coherent Light Source (LCLS) X-ray free-electron laser is enabled by angular streaking measurements.

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.

Upon exposure to ultra-intense, hard X-ray pulses, polyatomic molecules containing one heavy atom reach a much higher degree of ionization than do individual heavy atoms, contrary to previous assumptions.

Femtosecond X-ray Fourier holography imaging with record-high lateral resolution below 20 nm is demonstrated. Phase information is encoded into the interference of the diffraction patterns of a reference particle with a measurement sample.

Single Xe clusters are superheated using an intense optical laser pulse and the structural evolution is imaged with a single X-ray pulse. Ultrafast surface softening on the nanometre scale is resolved within 100 fs at the vacuum/sample interface.