Speaker
Description
High-gain harmonic generation (HGHG) is a seeding scheme for free-electron lasers (FELs), which improves the longitudinal coherence of the radiation output and reduces fluctuations of pulse energy, arrival time, and central wavelength compared to self-amplified spontaneous emission. In the HGHG scheme, laser-induced energy modulation is followed by a dispersive section, where part of the electrons form density maxima (“microbunches”) with the periodicity of the laser wavelength. The electrons between the microbunches have an energy spread correlated with the longitudinal coordinate. Longitudinal space charge (LSC) in a drift section tends to dilute the microbunches, while the correlated energy spread is reduced and even changes sign, if the drift section is long enough. In this case, a second dispersive section can be used to form new density maxima from the electrons between the initial microbunches, and the resulting energy modulation amplitude may be significantly larger than the initial one. Results from an experimental demonstration of this novel LSC-enhanced modulation scheme at FERMI, a seeded FEL user facility in Trieste, Italy, are presented.
Funding Agency
Work supported by Heinrich-Hertz-Stiftung, MKW NRW, and by BMFTR (contracts 05K22PE1, 05K22PE4)
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