Roussel E, Ferrari E, Allaria E, Penco G, Di Mitri S, Veronese M, Danailov M, Gauthier D, Giannessi L
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.
Phys Rev Lett. 2015 Nov 20;115(21):214801. doi: 10.1103/PhysRevLett.115.214801.
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.
激光加热系统是控制和优化工作在X射线波长范围内的高增益自由电子激光器（FEL）的重要工具。实际上，这些系统能使电子束的能量分散可控增加。这种加热抑制了纵向微聚束不稳定性，否则它会限制自由电子激光器的性能。在此，我们证明，通过微聚束不稳定性的作用，激光加热器在低能量时引起的电子束长波长调制可以一直持续到束流进入波荡器。这种相干纵向调制被用于控制自由电子激光器的光谱特性，特别是，通过激光加热器产生的调制与种子激光在电子束中产生的调制进行频率混合，可以产生多色极紫外自由电子激光脉冲。我们展示了在费米自由电子激光器上进行的这种新型配置的实验演示。
