Free Electron Laser: current status and challenges ahead.

The Free Electron Laser (FEL) is one of the historical activities of ENEA, where the relevant studies in the mid seventies of the last century started. The Agency researchers contributed to its theoretical and experimental understanding and to the development of the associated technologies, which created significant advantages in different fields of research. FELs have nowadays merged with synchrotron radiation sources and are expected to provide coherent radiation with unprecedented characteristics. In this article the various aspects of this tool are reviewed.