X-Ray Free-Electron Lasers: Beam Diagnostics, Beamline Instrumentation, and Applications II

With the successful start-up and operation of the first hard x-ray free-electron laser (FEL), the Linac Coherent Light Source (LCLS) at Stanford in April of 2009, and, more recently, the SPring-8 Angstrom Compact FEL, SACLA, in Japan in June of 2011, novel x-ray sources with unprecedented beam properties have become operational which offer great promise for exploring new scientific possibilities in ultrafast science with hard x-rays. These 4th-generation light sources operate in the self-amplified stimulated emission (SASE) mode and provide radiation with wavelengths typically as short as about 1Å and pulses of unrivaled brightness, brevity, peak power density, and transverse coherence, exceeding the values of the same parameters at 3rd Generation synchrotron radiation sources by up to ten orders of magnitude. The implementation of this class of sources using superconducting (SC) linac technology, as, for example in the European XFEL in Germany (planned operation in ca. 2015) and the FLASH VUV FEL, which has been successfully operating already since 2005, is also expected to match or exceed the time-averaged power density generated by most present-day sources by several orders of magnitude. Besides the above-mentioned facilities there are about a dozen other FELs currently being proposed or under construction all scheduled to become operational before 2020. The rapidly growing user community utilizes these sources for experiments in areas ranging from atomic physics, material science, x-ray diffraction, x-ray coherent imaging to high-energy-density physics. The experimental techniques are becoming increasingly complex posing great challenges for beam transport and beam shaping optics, diagnostics, detectors as well as synchronization techniques with optical lasers for pump probe experiments. Interpretation of scientific results necessitates the development and refinement of beam pulse diagnostic techniques. New developments are already underway to advance specialized schemes to generate ultra short pulses of a few femtoseconds, and various seeding techniques promising improved bandwidth and coherence properties which will involve novel directions in scientific applications.