X-Ray Free-Electron Laser

Abstract

During the last decade, the advent of the x-ray free electron lasers (XFELs) has opened a new research avenue for investigations of ultrafast electron and structure dynamics in any form of matter. XFELs deliver coherent x-ray pulses, combining unprecedented power densities up to 1020 W/cm2 and extremely short pulse durations down to a few femtoseconds, offering important advantages over conventional x-ray sources for many applications. Time-resolved spectroscopic and structure studies on the timescale of femtoseconds allow us to probe electrons and atoms in action. Indeed, XFELs have been applied to study ultrafast charge transfer in a molecule and a molecular complex, chemical bond breaking and formation, and phase transitions in solids. The intense coherent XFEL pulse focused down to 1 mm2 makes single-shot diffraction imaging of non-crystalized biomolecules and nano-size objects reality. On the other hand, since the XFEL pulses are entering a new regime of x-ray intensities, they are opening a new research field of studying interaction between intense x-ray pulses and various forms of matters. The extremely intense x-ray pulse strips off so many electrons from an isolated atom, leads to a violent Coulomb explosion of an isolated molecule, and transforms a solid target into extremely dense plasma. Furthermore, rapidly developing XFEL technologies make, not only fully coherent x-ray pulses available routinely, but also pulse shaping and phase-controlling of multicolor pulses reality, opening another novel research area of x-ray non-linear spectroscopy and attosecond coherent control.