Chirped pulse amplification in an extreme-ultraviolet free-electron laser

Chirped pulse amplification in optical lasers is a revolutionary technique, which allows thegeneration of extremely powerful femtosecond pulses in the infrared and visible spectralranges. Such pulses are nowadays an indispensable tool for a myriad of applications, both infundamental and applied research. In recent years, a strong need emerged for light sourcesproducing ultra-short and intense laser-like X-ray pulses, to be used for experiments in avariety of disciplines, ranging from physics and chemistry to biology and material sciences.This demand was satisfied by the advent of short-wavelength free-electron lasers. However,for any given free-electron laser setup, a limit presently exists in the generation of ultra-shortpulses carrying substantial energy. Here we present the experimental implementation ofchirped pulse amplification on a seeded free-electron laser in the extreme-ultraviolet, pavingthe way to the generation of fully coherent sub-femtosecond gigawatt pulses in the waterwindow (2.3–4.4 nm).