FEL photon diagnostics, instrumentation and beamlines design

For decades, synchrotron radiation sources have had the exclusive privilege of conducting X-ray science research. Now, X-ray science has a new forefront to explore: free-electron laser (FEL) based experiments.

Photon pulses with ultra-high brilliance, very short pulse lengths, unprecedented degree of coherence and wavefront quality produced by FELs have to be delivered either unperturbed or properly modified to the experimental stations. Together with the constant need for improved optical components and innovative detectors, one of the key factors to fully exploit the potential of such novel sources is the development and implementation of dedicated photon diagnostics. The measurement of the temporal and spectral structure of each single pulse, the knowledge of the effect of each optic on the wavefront, the non-invasive quantification of the power or intensity of each single pulse, and the optimisation of the focusing optics become of primary importance for the success of high-impact scientific experiments.

All these aspects of photon diagnostics, and the forefront technology in mirror fabrication and metrology as well as in X-ray detectors, were discussed at the PhotonDiag2015 Workshop on FEL Photon Diagnostics, Instrumentation and Beamlines Design. This special issue of the Journal of Synchrotron Radiation, guest-edited by Elke Plönjes (DESY), Marco Zangrando (Elettra) and Daniele Cocco (SLAC), presents a selection of papers from this meeting.