Abstract
We propose a new scheme to generate high-brightness and temporal coherent soft x-ray radiation in a seeded free-electron laser. The proposed scheme is based on the coherent harmonic generation (CHG) and superradiant principles. A CHG scheme is first used to generate a coherent signal at ultrahigh harmonics of the seed. This coherent signal is then amplified by a series of chicane-undulator modules via the fresh bunch and superradiant processes in the following radiator. Using a representative of a realistic set of parameters, three-dimensional simulations have been carried out and the simulations results demonstrated that 10 GW-level ultrashort ($\ensuremath{\sim}20\text{ }\text{ }\mathrm{fs}$) coherent radiation pulses in the water window can be achieved by using a 1.6 GeV electron beam based on the proposed technique.
Highlights
Intense, ultrashort, coherent soft x-ray pulses generated by free-electron lasers (FELs) are becoming an essential tool for achieving significant breakthroughs in various scientific domains such as femtochemistry, material science, biology, and so on
We propose a more straightforward method, termed high-brightness high-gain harmonic generation (HGHG) (HB-HGHG), to significantly enhance the output peak power of a seeded FEL
The HB-HGHG scheme has been proposed in this paper for enhancing the harmonic up-conversion efficiency and the output intensity of a seeded FEL
Summary
Ultrashort, coherent soft x-ray pulses generated by free-electron lasers (FELs) are becoming an essential tool for achieving significant breakthroughs in various scientific domains such as femtochemistry, material science, biology, and so on. The final output pulses from these schemes still suffer from large intensity or central wavelength fluctuations due to the energy jitter of the electron beam. An alternative way to significantly improve the temporal coherence of SASE relies on the manipulation of the electron beam longitudinal phase space through seeding schemes using external laser. An ultrashort coherent radiation pulse at the target harmonic of the seed laser is generated by a small part of the electron beam via the CHG process. This coherent signal is continually amplified by the fresh part of the electron beam in a long radiator with a series of temporal shifters to enhance the peak brightness of the FEL.
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