Optical resonator of powerful free-electron laser

The basic principles of calculation and design of an optical resonator for the high-power free-electron laser of the Siberian Center for Photochemical Research are presented. The resonator has two a time stage of development. The first is a so-called start optical resonator. The main task of the resonator is the determination of fundamental FEL parameters and search of optimal regimes. This resonator has adjustable output coupling and inner vacuum calorimeters for the measurement of high power. Only a small amount of the whole intra-cavity power is output to the atmosphere for diagnostic purposes. The second stage of the resonator has optimal output coupling and maximum output power for user applications. A method for a simple analytical calculation of losses in the laser resonator is described. Resonator losses measured by a fast Schottky detector are in reasonable agreement with calculated values