Owing to their ultra-high accelerating gradients, combined with injection inside micrometer-scale accelerating wakefield buckets, plasma-based accelerators hold great potential to drive a new generation of free-electron lasers (FELs). Indeed, the first demonstration of plasma-driven FEL gain was reported recently, representing a major milestone for the field. Several groups around the world are pursuing these novel light sources, with methodology varying in the use of wakefield driver (laser-driven or beam-driven), plasma structure, phase-space manipulation, beamline design, and undulator technology, among others. This paper presents our best attempt to provide a comprehensive overview of the global community efforts towards plasma-based FEL research and development.

High gain free electron laser devices, operating in the self amplified spontaneous emission regime, are under construction and was designed as the next generation of synchrotron radiation sources. In this paper we discuss the relevant physical aspects and derive simple relations for laser and higher order harmonic power, which can usefully be exploited in the preliminary design of these sources