High-repetition-rate seeding schemes using a resonator-amplifier setup

The spectral and temporal properties of Free-Electron Lasers (FEL) operating on the basis of self-amplified spontaneous emission (SASE) suffer from the stochastic behavior of the start-up process that fluctuates on a bunch-to-bunch basis. Several so-called ”seeding”-techniques using external radiation fields to overcome this limitation have been proposed and demonstrated. The external seed is usually generated by high-power laser systems, which are not yet available with a sufficient laser pulse energy at the high repetition rates of superconducting FEL facilities. In this contribution we discuss several seeding schemes that lower the requirements for the used laser systems, enabling seeded operation at high repetition rates by the means of a resonatoramplifier setup.