Two-stage seeded soft-X-ray free-electron laser

Abstract

We report the first generation of coherent, tunable, variable-polarization, soft X-ray femtosecond pulses, generated by a\ud seeded free-electron laser (FEL) operating in the fresh bunch, two-stage harmonic upshift configuration. Characterization\ud of the radiation proves this FEL configuration can produce single-transverse-mode, narrow-spectral-bandwidth output\ud pulses of several tens of microjoules energy and low pulse-to-pulse wavelength jitter at final wavelengths of 10.8 nm and\ud below. The fresh bunch configuration enhances the FEL emission at high harmonic orders by avoiding a gain depression\ud due to the energy spread induced by the first-stage FEL interaction. Coherent signals measured down to 4.3 nm suggest\ud this configuration is directly scalable to photon energies that will enable scientific investigations below the carbon K-edge,\ud including access to the L-edges of many magnetic materials, with an energy per pulse unlocking the gate for experiments\ud in the soft X-ray region with close to Fourier-transform-limited pulses

X-ray holography with a customizable reference

“…The experiment was performed at FERMI [24][25][26] , a seeded soft X-ray free-electron laser. It is a highly suitable source for coherent X-ray imaging because of its high brightness and excellent coherence properties 8 .…”

Echoes of photons past

“…One is High Gain Harmonic Generation 5 (HGHG), a process which may be cascaded to obtain larger harmonic upshifts 6 . However, as its name suggests, this process relies upon the high-gain FEL mechanism so that, unlike EEHG, the effects of intrinsic noise or beam inhomogeneities can become amplified during the harmonic up-shifting process, limiting the total harmonic upshift achievable 7,8 .…”

Direct Phasing of Finite Crystals Illuminated with a Free-Electron Laser

“…Measurements were carried out at the coherent diffraction imaging (CDI) experimental station at the DiProI beamline [37] of the FERMI@Elettra FEL [38][39][40]. We chose to perform our investigations at an FEL source so that the relevant effects of shot-by-shot wavefront phase and intensity variations would be present in our data.…”