Historical Survey of Free Electron Lasers

Abstract

Free electron lasers are presently unique tuneable powerful lasers ranging from the infrared to the X-ray, serving for the exploration of light–matter interaction.They make use of a simple and elegant gain medium. The coherent radiation is generated using free electrons in a periodic permanent magnetic field generated by a so-called undulator as an amplification medium. The light–electron interaction in the undulator leads to a bunching process, setting in phase the electron emitters and establishing a longitudinal coherence. The amplifica-tion of the light wave takes place to the detriment of the kinetic energy of the electrons. First, the origins of the free electron laser, starting from the photon–matter interaction, the early times of synchrotron radiation and the undulator, the development of vacuum tubes, masers, and lasers are introduced. Then, motivated by the search of an exotic laser, the invention of the free electron conceptual idea laser is discussed, with a quantum approach followed by a classical one. The first low gain free electron laser experiments are then presented. Finally, some insight is given in the case of the high gain free electron lasers.