THE PHYSICS OF FREE-ELECTRON LASERS - AN INTRODUCTION

The present paper contains a systematic exposure of basic principles of free electron laser physics. FEL models are discussed wherein space charge fields, energy spread of the electrons in the beam and diffraction effects are taken into account. We present a detailed study of the one-dimensional theory of a FEL amplifier, FEL oscillator and FEL oscillator with multicomponent undulator. We present also an introduction to the analysis of the diffraction effects using the FEL amplifier model. When exposing linear theory we use analytical techniques and the investigation of nonlinear modes in the operation of FEL devices is performed using the results of numerical simulations. The results of the linear theory serve as a primary standard to check the accuracy of numerical simulations. We perform a thorough analysis of the saturation effects in the FEL devices and of the methods to increase the FEL efficiency. A theoretical study is performed with a wide use of similarity techniques, so the obtained results are simultaneously of high degree of generality and completely specified. Numerous universal graphs illustrating various modes of the FEL operation together with the reduced design formulae can help the reader to find FEL characteristics using simple dimensional analysis only. It may be useful also for FEL designers, especially at the design stage of an experiment.