title: Multicolor High-Gain Free-Electron Laser Driven by Seeded Microbunching Instability.
abstract: Laser-heater systems are essential tools to control and optimize high-gain free-electron lasers (FELs) working in the x-ray wavelength range. Indeed, these systems induce a controllable increase of the energy spread of the electron bunch. The heating suppresses longitudinal microbunching instability which otherwise would limit the FEL performance. Here, we demonstrate that, through the action of the microbunching instability, a long-wavelength modulation of the electron beam induced by the laser heater at low energy can persist until the beam entrance into the undulators. This coherent longitudinal modulation is exploited to control the FEL spectral properties, in particular, multicolor extreme-ultraviolet FEL pulses can be generated through a frequency mixing of the modulations produced by the laser heater and the seed laser in the electron beam. We present an experimental demonstration of this novel configuration carried out at the FERMI FEL.
authors.affiliation: Elettra-Sincrotrone Trieste, Strada Statale 14-km 163,5 in AREA Science Park, 34149 Basovizza, Trieste, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Roussel
authors.affiliation: Elettra-Sincrotrone Trieste, Strada Statale 14-km 163,5 in AREA Science Park, 34149 Basovizza, Trieste, Italy.|Università degli Studi di Trieste, Dipartimento di Fisica, Piazzale Europa 1, 34127 Trieste, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Ferrari
authors.affiliation: Elettra-Sincrotrone Trieste, Strada Statale 14-km 163,5 in AREA Science Park, 34149 Basovizza, Trieste, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Allaria
authors.affiliation: Elettra-Sincrotrone Trieste, Strada Statale 14-km 163,5 in AREA Science Park, 34149 Basovizza, Trieste, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Penco
authors.affiliation: Elettra-Sincrotrone Trieste, Strada Statale 14-km 163,5 in AREA Science Park, 34149 Basovizza, Trieste, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Di Mitri
authors.affiliation: Elettra-Sincrotrone Trieste, Strada Statale 14-km 163,5 in AREA Science Park, 34149 Basovizza, Trieste, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Veronese
authors.affiliation: Elettra-Sincrotrone Trieste, Strada Statale 14-km 163,5 in AREA Science Park, 34149 Basovizza, Trieste, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Danailov
authors.affiliation: Elettra-Sincrotrone Trieste, Strada Statale 14-km 163,5 in AREA Science Park, 34149 Basovizza, Trieste, Italy.
authors.forename: D
authors.initials: D
authors.lastname: Gauthier
authors.affiliation: Elettra-Sincrotrone Trieste, Strada Statale 14-km 163,5 in AREA Science Park, 34149 Basovizza, Trieste, Italy.|ENEA Frascati, Via E. Fermi 45, 00044 Frascati, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Giannessi