Triple modulator-chicane scheme for seeding sub-nanometer x-ray free-electron lasers

Abstract

We propose a novel triple modulator-chicane (TMC) scheme to convert external input seed into shorter wavelengths. In this scheme, high-power seed lasers are used in the first and the third modulator, while only a very-lowpower seed is used in the second modulator. By properly choosing the parameters of the lasers and chicanes, we show that ultrahigh harmonics can be generated in the TMC scheme while simultaneously keeping the energy spread growth much smaller than the beam's initial slice energy spread. As an example, we show the feasibility of generating significant bunching at 1 nm and below from a lowpower (∼100 kW) high harmonic generation seed at 20 nm assisted by two highpower (∼100MW) UV lasers at 200 nm while keeping the energy spread growth within 40%. The supreme up-frequency conversion efficiency of the proposed TMC scheme, together with its unique advantage in maintaining beam energy spread, opens up new opportunities for generating fully coherent x-rays at subnanometer wavelength from external seeds.© IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.