Laboratoire de Chimie Physique – Matière et Rayonnement
UMR 7614, Université Pierre et Marie Curie
With the advent of X-ray Free Electron Lasers (XFEL), a novel type of X-ray light source with unprecedented beam properties has become available. Key parameters have an intensity of about 10^12 photons per pulse, a pulse duration that can be tuned from several hundreds down to the sub-femtosecond time scale, and a very high degree of coherence (and thus a high photon degeneracy). Started as the TESLA Test Facility, FLASH in Hamburg (Germany) was the first XFEL opening as a general user facility in 2005. It covers today with its first harmonic the photon energy range from a few tens up to about 300 eV (XUV-FEL). In 2009, first lasing in the hard X-ray photon energy range was demonstrated at LCLS in Stanford (USA). The hard X-ray FEL SACLA in Japan and the XUV-FEL FERMI in Italy have become operational in 2012 and the hard X-ray FEL PAL-XFEL in Korea followed in 2016. In 2017 commissioning has started of the hard X-ray FELs SwissFEL (Switzerland) and the European XFEL (Germany), of which France is a member country. It is thus very timely to update the communities interested in time resolved X-ray (or more generally, photon based) experiments about the current performance of these sources and to indicate the future perspectives of these sources. To do so, I will start out with a general overview of these sources and their key parameters and then discuss a series of recent scientific highlights, which exploit the different key properties of these unique facilities and which underline the diverse research areas pursued at these sources already today.