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X-ray free-electron laser is a power probe for materials, but it is challenging to measure the spectro-temporal characters of individual pulses. Here, De Ninno et al.implement an interferometric method allowing one to characterize and control the ultrashort XUV pulses seeded by a femtosecond laser.

Short laser pulses of femtosecond time scales are in high demand in order to explore the fast electron dynamics in light-matter interactions. Here, the authors demonstrated the compression of free electron laser pulses in the extreme ultraviolet range by using a chirped pulse amplification technique.

Core excitons are strongly localised excitonic states impacting x-ray absorption and resonant inelastic scattering (RIXS) spectra. Here, the authors demonstrate an application of free electron laser-driven ultrafast RIXS spectroscopy to study previously unclear aspects of core exciton-phonon interactions in graphite.

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.

A seeded free-electron laser with a two-stage harmonic upshift configuration provided tunable and coherent soft-X-ray pulses. The configuration produced single-transverse-mode, narrow-spectral-bandwidth femtosecond pulses with energies of several tens of microjoules and a low pulse-to-pulse wavelength jitter at wavelengths of 10.8 nm and below.

Researchers demonstrate the FERMI free-electron laser operating in the high-gain harmonic generation regime, allowing high stability, transverse and longitudinal coherence and polarization control.

Ultrafast quantum control of helium atoms is obtained by shaping the extreme ultraviolet pulses generated by a seeded free-electron laser.

Light-induced ultrafast switching between the molecular isomers norbornadiene and quadricyclane can reversibly store and release a substantial amount of chemical energy. Two competing pathways have now been identified by which electronically excited quadricyclane molecules relax to the electronic ground state, facilitating interconversion between the two isomers on different timescales.

Free-electron lasers are a powerful new tool for studying properties and transient states of matter. Here, the authors use a novel seed scheme for generation of two XUV laser pulses of controlled wavelength and time separation that enables access to ultrafast phenomena with elemental sensitivity.

Relative synchronization between free-electron laser pulses and a near-infrared field fields is achieved with 24 as resolution by using a correlation analysis of single-shot photoelectron spectra. It is applied to coherently control the photoionization process in neon atom on the attosecond timescale.

Two-colour X-ray free electron laser is a powerful tool for pump–probe measurements, but currently constrained by limited tunability. Here, Ferrari et al. develop a configuration that allows tuning both the pump and the probe to specific electronic excitations, providing element selectivity.

By amplifying a soliton in a multistage cascade, few-femtosecond extreme-ultraviolet free-electron laser pulses are achieved.

Generation of intense attosecond waveforms with independently controllable amplitude and phase is performed by using a seeded free-electron laser.

Echo-enabled harmonic generation in a free-electron laser enables 45th harmonic pulses from a 264 nm wavelength seed, yielding 5.9 nm wavelength coherent output.

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.

Light pulses with controllable parameters are desired for studying the fundamental properties of matter. Here the authors generate and use phase-manipulated and highly time-stable XUV pulse pairs to probe the coherent evolution and dephasing of XUV electronic coherences in helium and argon.

There is interest in understanding the relaxation mechanisms of photoexcitation in atoms, molecules and other complex systems. Here the authors unravel the photoexcitation and ultrafast relaxation of superfluid helium nanodroplets using a pump-probe experiment with FEL pulses.

Photoinduced isomerization reactions, including ring-opening reactions, lie at the heart of many chemical processes in nature. The pathway and dynamics of the ring opening of a model heterocycle have now been investigated by femtosecond photoelectron spectroscopy combined with ab initio theory, enabling the visualization of rich dynamics in both the ground and excited electronic states.

The first steps in photochemical processes involve changes in electronic and geometric structure on extremely short timescales. Here, the authors report femtosecond dynamics in prototypical acetylacetone, by pump-probe photoexcitation-photoemission experiments and static and dynamics calculations.

The findings that the spatial distribution of an optical field with vortex phase profile can be imprinted coherently onto a propagating electron wave reveal new aspects of light–matter interactions and will help develop future single-photon electron spectroscopy.

Attosecond pulse trains, crucial for ultrafast science, traditionally consist of only odd harmonics due to symmetry constraints in high-order harmonic generation. Here, the authors extend the RABBIT technique to analyze non-consecutive harmonics, enabling the temporal reconstruction of attosecond pulse trains and advancing metrology in extreme ultraviolet spectroscopy.