Surface Science Studies with Free Electron Lasers: Real-Time Observations of Electronic Structure Changes during Reactions

New light sources based on linear accelerators such as FLASH at DESY in Hamburg, the first free-electron laser in the extreme ultraviolet (XUV) and soft X-ray regime, which started user operation in 2005 1 W. Ackermann, Nature Photonics 1, 336–342 (2007).Crossref], Web of Science ®] , Google Scholar]], the Linac Coherent Light Source LCLS in Stanford 2 P. Emma, Nature Photonics 4, 641–647 (2010).Crossref], Web of Science ®] , Google Scholar]], and SACLA at Spring-8 in Japan 3 T. Ishikawa, Nature Photonics 6, 540–544 (2012).Crossref], Web of Science ®] , Google Scholar]], as X-ray lasers dedicated to the hard X-ray regime down to below 1 Å in wavelength, or FERMI at ELETTRA in Trieste 4 E. Allaria, Nature Photonics 6, 699–704 (2012).Crossref], Web of Science ®] , Google Scholar]] as the first fully externally seeded free electron laser also operating in the XUV and soft X-ray regime, provide ultrashort, extremely powerful, short wavelength pulses with unprecedented coherence properties. With the European XFEL in Hamburg, the Swiss FEL at PSI in Villigen, Switzerland, and the PAL-XFEL in Pohang, Korea, three more FELs are expected to produce first light by the end of 2016 and the beginning of 2017, respectively.