Free electron laser oscillator efficiency

The efficiency of Free Electron Laser (FEL) Oscillator devices is a fairly complicated function of the various parameters which characterize the device itself. We explore the relevant dependences by the use of the scaling formulas describing the FEL Oscillator dynamics and providing the relevant design elements. We obtain a quantitative dependence of the efficiency on the key FEL parameters (small signal gain coefficient, saturation intensity, electron beam qualities...) and discuss the use of the results obtained in the paper as a further element for the FEL Oscillator optimization.