Gain of the LELA free electron laser and characteristics of the optical cavity

Abstract After a brief discussion of the influence of the e-beam finite emittance on the small signal gain of the LELA free electron laser, the optical cavity of the FEL built on the ADONE storage ring in Frascati is described. Particular attention is devoted to the description of the alignment and tuning problems, both of which have been solved by means of a remote control system.