FEMTOSECOND STABLE LASER-TO-RF PHASE DETECTION USING OPTICAL MODULATORS

Free-Electron Lasers like FLASH and the European XFEL require the synchronization of RF stations to the optical timing reference of the accelerator. For this purpose, a new technique to phase-lock RF sources to an optical pulse train has been invented. The new technique uses an opto-microwave coupling device together with an ultra-low phase-noise RF source operating at a frequency of 1.3 GHz. In our arrangement, the Laser-to-RF phase detector is insensitive to amplitude fluctuations of the optical reference pulse train, which allows the detector to achieve femtosecond precision over long time periods. In this paper, we present the balanced Laser-to-RF phase detection principle along with a tolerance study of the arrangement and first results from our prototype setup.