10.1117/2.1200905.1566 The quantum free-electron laser

An ultracompact brilliant coherent x-ray source, where both the accele-rator and the wiggler are provided by intense laser pulses, promises unsurpassed spectral and temporal qualities. Ultrashort pulses of x-ray radiation from synchrotron sources have become ubiquitous tools for investigating the structure of matter. Their immense usefulness has led to the develop-ment of large international facilities. These are based on radio-frequency accelerating cavities and magnetic undulators, and provide brief radiation pulses capable of probing and taking ‘snapshots ’ of molecules and solid-state matter. However, syn-chrotron sources produce pulses of incoherent radiation that are limited to relatively low peak brilliance and durations of order a picosecond and longer. As a next significant step in advancing x-ray sources, the free-electron laser (FEL) produces femtosecond-duration pulses with a peak brilliance seven orders of magni-tude higher than synchrotrons. Several large international teams are constructing FELs to pro-duce x-ray radiation through self-amplified spontaneous emis