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

TL;DR

This paper introduces a novel seeded free-electron laser technique that significantly reduces seed laser power requirements, enabling high-repetition-rate, fully coherent EUV and X-ray radiation with stable high power.

Contribution

A new method employing a long modulator for laser amplification and electron modulation, allowing MHz repetition rates and high coherence with lower seed laser power.

Findings

Seed laser power reduced by about three orders of magnitude.

FEL radiation maintains high coherence and power stability.

Enables realization of MHz repetition-rate EUV and X-ray FELs.

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.