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

Rebernik Ribic, P.; Abrami, A.; Badano, L.; Bossi, M.; Braun, H. -H.; Bruchon, N.; Capotondi, F.; Castronovo, D.; Cautero, M.; Cinquegrana, P.; Coreno, M.; Couprie, M. E.; Cudin, I.; Boyanov Danailov, M.; De Ninno, G.; Demidovich, A.; Di Mitri, S.; Diviacco, B.; Fawley, W. M.; 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, N. S.; Petrov Nikolov, I.; Penco, G. M.; 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.; Trovo, M.; Veronese, M.; Vivoda, D.; Xiang, D.; Zaccaria, M.; Zangrando, D.; Zangrando, M.; Allaria, E. M.

doi:10.1038/s41566-019-0427-1

X-ray free-electron lasers (FELs), which amplify light emitted by a relativistic electron beam, are extending nonlinear optical tech- niques 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) con- figuration. 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 wave- lengths as short as 5.9 nm (~211 eV) at the FERMI FEL user facility. Low sensitivity to electron-beam imperfections and observa- tion 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.

Coherent soft X-ray pulses from an echo-enabled harmonic generation free-electron laser / Rebernik Ribic, P.; Abrami, A.; Badano, L.; Bossi, M.; Braun, H. -H.; Bruchon, N.; Capotondi, F.; Castronovo, D.; Cautero, M.; Cinquegrana, P.; Coreno, M.; Couprie, M. E.; Cudin, I.; Boyanov Danailov, M.; De Ninno, G.; Demidovich, A.; Di Mitri, S.; Diviacco, B.; Fawley, W. M.; 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, N. S.; Petrov Nikolov, I.; Penco, G. M.; 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.; Trovo, M.; Veronese, M.; Vivoda, D.; Xiang, D.; Zaccaria, M.; Zangrando, D.; Zangrando, M.; Allaria, E. M.. - In: NATURE PHOTONICS. - ISSN 1749-4885. - 13:8(2019), pp. 555-561. [10.1038/s41566-019-0427-1]