Free-electron lasers

A review of free-electron lasers (FELs) is presented. Recent advances in increasing the power, improving the efficiency, and operating at shorter wavelengths have pushed the FEL to the forefront in the quest for ultrahigh-power lasers. The tunability of FELs is beginning to be exploited for medical applications and other basic research programs. The important properties of the FEL are discussed, and a history of the experiments leading up to the state-of-the-art devices is presented. Some important technical issues, which must be dealt with in the design of any FEL, are described. A brief look at the future of FEL research is given.