Over more than a century, X-rays have transformed our understanding of the fundamental
structure of matter and have been an indispensable tool for chemistry, physics, biology …

This review is focused on free-electron lasers (FELs) in the hard to soft x-ray regime. The
aim is to provide newcomers to the area with insights into: the basic physics of FELs, the …

Four-wave mixing (FWM) processes, based on third-order nonlinear light–matter
interactions, can combine ultrafast time resolution with energy and wavevector selectivity …

Many advanced applications of X-ray free-electron lasers require pulse durations and time
resolutions of only a few femtoseconds. To generate these pulses and to apply them in time …

In ultrafast spectroscopy, the temporal resolution of time-resolved experiments depends on
the duration of the pump and probe pulses, and on the control and characterization of their …

The recent construction of free electron lasers allows extending laboratory-based laser
experiments to shorter wavelengths, accessing wavevectors typical of nanoscale dynamics …

FERMI is a seeded free-electron laser (FEL) facility located at the Elettra laboratory in
Trieste, Italy, and is now in user operation with its first FEL line, FEL-1, covering the …

Attosecond pulses are central to the investigation of valence-and core-electron dynamics on
their natural timescales,–. The reproducible generation and characterization of attosecond …

The pulse duration, and, more generally, the temporal intensity profile of free-electron laser
(FEL) pulses, is of utmost importance for exploring the new perspectives offered by FELs; it …

Free-electron lasers producing ultrashort pulses with high peak power promise to extend
ultrafast non-linear spectroscopic techniques into the extreme-ultraviolet–X-ray regime. Key …