High-repetition-rate seeded free-electron laser with direct-amplification of an external coherent laser

Abstract

Various scientific and industrial researches such as spectroscopy and advanced nano-technologies have been demanding high flux and fully coherent EUV and X-ray radiation. These demands can be commendably satisfied with a MHz-level repetition-rate seeded free-electron laser (FEL). Dictated by the seed laser system, seeded FELs have faced obstacles for the realization of MHz repetition rate. Reducing the required peak power of an external coherent seed laser can effectively increase the repetition rate of a seeded FEL. This paper presents a novel technique that employs a long modulator as a carrier for laser amplification and electron modulation, which is quite different from nominal seeded FELs. Applications of the proposed technique into high-gain harmonic generation (HGHG) and echo-enabled harmonic generation (EEHG) are investigated. Simulation results demonstrate that seed laser power is reduced by about three orders of magnitude and the FEL radiation possesses consistently high coherence and power stability with respect to the nominal HGHG or EEHG. The proposed technique paves the way for the realization of fully coherent EUV and soft X-ray FELs with a repetition rate of MHz and an average power of about 100 W.

High-repetition-rate seeded free-electron laser enhanced by self-modulation

“… – 37 In addition, a resonator-like seed recirculation feedback system has been proposed to reuse the radiation in the modulator section to modulate the following electron bunches 38 – 41 The use of a relatively longer modulator has been suggested to reduce the peak power requirements of the external seed laser 32 , 42 , 43 . More analysis of various methods to high-repetition-rate seeded FELs has been studied 44 .…”

“…[38][39][40][41] The use of a relatively longer modulator has been suggested to reduce the peak power requirements of the external seed laser. 32,42,43 More analysis of various methods to high-repetition-rate seeded FELs has been studied. 44 Compared with the seeded oscillator-amplifier scheme 40 and the modulator lengthening scheme, 43 the self-modulation scheme 30 does not require extra optical elements or a considerably long modulator.…”

“…32,42,43 More analysis of various methods to high-repetition-rate seeded FELs has been studied. 44 Compared with the seeded oscillator-amplifier scheme 40 and the modulator lengthening scheme, 43 the self-modulation scheme 30 does not require extra optical elements or a considerably long modulator. The self-modulation scheme can be easily applied to all existing seeded FEL facilities with minimal hardware addition, especially in synergy with EEHG setups.…”

High-repetition-rate seeded free-electron laser enhanced by self-modulation

“…In addition, a resonator-like seed recirculation feedback system is proposed to reuse the radiation in the modulator section to modulate the following electron bunches [31][32][33]. The use of a relatively longer modulator has been suggested to reduce the peak power requirements of the external seed laser [34][35][36]. Recently, the self-modulation of the electron beam has been experimentally demonstrated to be an effective method of reducing the requirement for an external seed laser [37,38].…”

Enhanced harmonic generation for high-repetition-rate soft x-ray free-electron laser

“…However, due to state-of-the-art laser system limitations, the ultraviolet (UV) seed laser is challenging to induce sufficient energy modulation with high repetition rates. Recently, the self-modulation scheme experimentally demonstrated that the peak power requirement of a seed laser could be reduced by around one order of magnitude in an HGHG setup [7,8]. In this paper, start-to-end simulations of the self-modulation-enhanced HB-HGHG scheme [9] are conducted with realistic electron beam parameters of the SXFEL user facility.…”