Storage ring free electron laser: operation with two undulators having opposite circular polarizations

In Storage Ring Free Electron Lasers two undulators, having opposite helical polarizations and arranged as an Optical-Klystron, may be exploited to obtain linearly polarized radiation, without additional problems associated with mirror degradation, due to the higher on axis harmonic emission. In this paper we explore the dynamical behavior of this device and discuss possible configurations allowing such a possibility.