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Intense extreme UV and X-ray coherent sources are set to revolutionize numerous research areas, yet characterization of their polarization remains elusive. Here, Mazza et al.measure the polarization state of circularly polarized extreme UV light from a free-electron laser using circular dichroism.

Electrons in atoms exhibit many-body collective behaviours that can be studied by highbrightness X-rays from FELs. Here, the authors examine two-photon above threshold ionization of xenon and find that nonlinearities in the response uncover that more than one state underpins the 4dgiant resonance.

Exploring the photoionization process leads to better understanding of the fundamental interactions between light and matter. Here the authors show the non-dipole contribution in the form of asymmetric photoelectron angular distribution from the ionization of argon atoms and ions.

The first operation of the European X-ray free-electron laser facility accelerator based on superconducting technology is reported. The maximum electron energy is 17.5 GeV. A laser average power of 6 W is achieved at a photon energy of 9.3 keV.

Intense light pulses can create nonlinear ionization processes in atoms and molecules. Here the authors study the photoionization of xenon atoms using intense free-electron laser pulses that can create extremely high charge states and produce hollow atoms, featuring up to six simultaneous core-holes.

Visualizing the structural dynamics of isolated molecules would help to understand chemical reactions, but this is difficult for complex structures. Intense femtosecond X-ray pulses allow the full imaging of exploding photoionized molecules, in this case, with eleven atoms.

Few-femtosecond synchronization at free-electron lasers is key for nearly all experimental applications, stable operation and future light source development. Here, Schulz et al. demonstrate all-optical synchronization of the soft X-ray FEL FLASH to better than 30 fs and illustrate a pathway to sub-10 fs.

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.

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.

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.

Coincidence experiments at free-electron lasers enable time resolved site-specific investigations of molecular photochemistry at high signal rates, but isolating individual dissociation processes still poses a considerable technical challenge. Here, the authors use electron-ion partial covariance imaging to isolate otherwise elusive chemical shifts in UV-induced photofragmentation pathways of the prototypical chiral molecule 1-iodo-2-methylbutane.

Ultrashort circularly polarised light pulses from free-electron lasers offer a route for exploring chiral molecules and their dynamics, but remain challenging to harness. Here, X-ray pump-probe experiments enable a site-specific photoelectron circular dichroism measurement on a dissociating chiral molecule.