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Open Access Publications from the University of California

Coherent soft X-ray pulses from an echo-enabled harmonic generation free-electron laser

  • Author(s): Rebernik Ribič, P
  • Abrami, A
  • Badano, L
  • Bossi, M
  • Braun, HH
  • Bruchon, N
  • Capotondi, F
  • Castronovo, D
  • Cautero, M
  • Cinquegrana, P
  • Coreno, M
  • Couprie, ME
  • Cudin, I
  • Boyanov Danailov, M
  • De Ninno, G
  • Demidovich, A
  • Di Mitri, S
  • Diviacco, B
  • Fawley, WM
  • Feng, C
  • Ferianis, M
  • Ferrari, E
  • Foglia, L
  • Frassetto, F
  • Gaio, G
  • Garzella, D
  • Ghaith, A
  • Giacuzzo, F
  • Giannessi, L
  • Grattoni, V
  • Grulja, S
  • Hemsing, E
  • Iazzourene, F
  • Kurdi, G
  • Lonza, M
  • Mahne, N
  • Malvestuto, M
  • Manfredda, M
  • Masciovecchio, C
  • Miotti, P
  • Mirian, NS
  • Petrov Nikolov, I
  • Penco, GM
  • Penn, G
  • Poletto, L
  • Pop, M
  • Prat, E
  • Principi, E
  • Raimondi, L
  • Reiche, S
  • Roussel, E
  • Sauro, R
  • Scafuri, C
  • Sigalotti, P
  • Spampinati, S
  • Spezzani, C
  • Sturari, L
  • Svandrlik, M
  • Tanikawa, T
  • Trovó, M
  • Veronese, M
  • Vivoda, D
  • Xiang, D
  • Zaccaria, M
  • Zangrando, D
  • Zangrando, M
  • Allaria, EM
  • et al.

X-ray free-electron lasers (FELs), which amplify light emitted by a relativistic electron beam, are extending nonlinear optical techniques to shorter wavelengths, adding element specificity by exciting and probing electronic transitions from core levels. These techniques would benefit tremendously from having a stable FEL source, generating spectrally pure and wavelength-tunable pulses. We show that such requirements can be met by operating the FEL in the so-called echo-enabled harmonic generation (EEHG) configuration. Here, two external conventional lasers are used to precisely tailor the longitudinal phase space of the electron beam before emission of X-rays. We demonstrate high-gain EEHG lasing producing stable, intense, nearly fully coherent pulses at wavelengths as short as 5.9 nm (~211 eV) at the FERMI FEL user facility. Low sensitivity to electron-beam imperfections and observation of stable, narrow-band, coherent emission down to 2.6 nm (~474 eV) make the technique a prime candidate for generating laser-like pulses in the X-ray spectral region, opening the door to multidimensional coherent spectroscopies at short wavelengths.

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