Study on the seed laser phase error multiplication in seeded free electron lasers

Seeded free-electron lasers (FELs) hold a great promise for generating high brilliant radiation with a narrow bandwidth. However, it has been pointed out that the initial seed laser noise will be amplified in the harmonic up-conversion process, which may degrade the output radiation pulse quality of a seeded FEL. In this paper, theoretical and simulation studies of seeded FEL schemes with seed laser imperfections are presented. It is found that the slippage effect in the modulator will slow down the multiplication process of the seed laser phase error, which may aid in the production of transform-limited short-wavelength pulses for seeded FELs.