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Generation and measurement of intense few-femtosecond superradiant extreme-ultraviolet free-electron laser pulses


Free-electron lasers producing ultrashort pulses with high peak power promise to extend ultrafast non-linear spectroscopic techniques into the extreme-ultraviolet–X-ray regime. Key aspects are the synchronization between pump and probe, and the control of the pulse properties (duration, intensity and coherence). Externally seeded free-electron lasers produce coherent pulses that can be synchronized with femtosecond accuracy. An important goal is to shorten the pulse duration, but the simple approach of shortening the seed is not sufficient because of the finite-gain bandwidth of the conversion process. An alternative is the amplification of a soliton in a multistage, superradiant cascade: here, we demonstrate the generation of few-femtosecond extreme-ultraviolet pulses, whose duration we measure by autocorrelation. We achieve pulses four times shorter, and with a higher peak power, than in the standard high-gain harmonic generation mode and we prove that the pulse duration matches the Fourier transform limit of the spectral intensity distribution.

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Fig. 1: FEL layout.
Fig. 2: Pulse duration.
Fig. 3: Pulse energy.
Fig. 4: Pulse spectrum.
Fig. 5: Frequency pulling.

Data availability

Source data are provided with this paper. The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

Code availability

The simulation reported in Fig. 4 was carried out with version 2 and version 4 of the code GENESIS 1.3 available at and


  1. Schreck, S., Beye, M. & Föhlisch, A. Implications of stimulated resonant X-ray scattering for spectroscopy, imaging, and diffraction in the regime from soft to hard X-rays. J. Mod. Opt. 62, S34–S45 (2015).

    ADS  MathSciNet  MATH  Google Scholar 

  2. Calegari, F. et al. Ultrafast electron dynamics in phenylalanine initiated by attosecond pulses. Science 346, 336–339 (2014).

    ADS  Google Scholar 

  3. Berrah, N. A perspective for investigating photo-induced molecular dynamics from within with femtosecond free electron lasers. Phys. Chem. Chem. Phys. 19, 19536–19544 (2017).

    Google Scholar 

  4. Rudenko, A. et al. Femtosecond response of polyatomic molecules to ultra-intense hard X-rays. Nature 546, 129–132 (2017).

    ADS  Google Scholar 

  5. Bencivenga, F., Capotondi, F., Principi, E., Kiskinova, M. & Masciovecchio, C. Coherent and transient states studied with extreme ultraviolet and X-ray free electron lasers: present and future prospects. Adv. Phys. 63, 327–404 (2015).

    ADS  Google Scholar 

  6. Prince, K. C. et al. Coherent control with a short-wavelength free-electron laser. Nat. Photonics 10, 176–179 (2016).

    ADS  Google Scholar 

  7. Danailov, M. B. et al. Towards jitter-free pump-probe measurements at seeded free electron laser facilities. Opt. Express 22, 12869–12879 (2014).

    ADS  Google Scholar 

  8. Allaria, E. et al. Highly coherent and stable pulses from the FERMI seeded free-electron laser in the extreme ultraviolet. Nat. Photonics 6, 699–704 (2012).

    ADS  Google Scholar 

  9. De Ninno, G. et al. Single-shot spectro-temporal characterization of XUV pulses from a seeded free-electron laser. Nat. Commun. 6, 8075 (2015).

    ADS  Google Scholar 

  10. Gorobtsov, O. Y. et al. Seeded X-ray free-electron laser generating radiation with laser statistical properties. Nat. Commun. 9, 4498 (2018).

    ADS  Google Scholar 

  11. Finetti, P. et al. Pulse duration of seeded free-electron lasers. Phys. Rev. X 7, 021043 (2017).

    Google Scholar 

  12. Allaria, E. et al. Two-colour pump–probe experiments with a twin-pulse-seed extreme ultraviolet free-electron laser. Nat. Commun. 4, 2476 (2013).

    ADS  Google Scholar 

  13. McNeil, B. W. J., Thompson, N. R., Dunning, D. J. & Sheehy, B. High harmonic attosecond pulse train amplification in a free electron laser. J. Phys. B 44, 065404 (2011).

    ADS  Google Scholar 

  14. Gauthier, D. et al. Chirped pulse amplification in an extreme-ultraviolet free-electron laser. Nat. Commun. 7, 13688 (2016).

    ADS  Google Scholar 

  15. Tanaka, T. & Rebernic Ribič, P. Shortening the pulse duration in seeded free-electron lasers by chirped microbunching. Opt. Express 27, 30875–30892 (2019).

    ADS  Google Scholar 

  16. Maroju, P. K. et al. Attosecond pulse shaping using a seeded free-electron laser. Nature 578, 386–391 (2020).

    ADS  Google Scholar 

  17. Duris, J. et al. Tunable isolated attosecond X-ray pulses with gigawatt peak power from a free-electron laser. Nat. Photonics 14, 30–36 (2020).

    Google Scholar 

  18. Emma, P. et al. Femtosecond and subfemtosecond X-ray pulses from a self-amplified spontaneous-emission based free-electron laser. Phys. Rev. Lett. 92, 074801 (2004).

    ADS  Google Scholar 

  19. Marinelli, A. et al. Optical shaping of X-ray free-electron lasers. Phys. Rev. Lett. 116, 254801 (2016).

    ADS  Google Scholar 

  20. Behrens, C. et al. Few-femtosecond time-resolved measurements of X-ray free-electron lasers. Nat. Commun. 5, 3762 (2014).

    ADS  Google Scholar 

  21. Ding, Y. et al. Generating femtosecond X-ray pulses using an emittance-spoiling foil in free-electron lasers. Appl. Phys. Lett. 107, 191104 (2015).

    ADS  Google Scholar 

  22. Zholents, A. A. & Penn, G. Obtaining attosecond x-ray pulses using a self-amplified spontaneous emission free electron laser. Phys. Rev. Spec. Top. Accel. Beams 8, 050704 (2005).

    ADS  Google Scholar 

  23. Guetg, M. W. et al. Generation of high-power high-intensity short X-ray free-electron-laser pulses. Phys. Rev. Lett. 120, 014801 (2018).

    ADS  Google Scholar 

  24. Ding, Y. et al. Beam shaping to improve the free-electron laser performance at the Linac Coherent Light Source. Phys. Rev. Accel. Beams 19, 100703 (2016).

    ADS  Google Scholar 

  25. Huang, S. et al. Generating single-spike hard X-ray pulses with nonlinear bunch compression in free-electron lasers. Phys. Rev. Lett. 119, 154801 (2017).

    ADS  Google Scholar 

  26. Marinelli, A. et al. Experimental demonstration of a single-spike hard-X-ray free-electron laser starting from noise. Appl. Phys. Lett. 111, 151101 (2017).

    ADS  Google Scholar 

  27. Giannessi, L., Musumeci, P. & Spampinati, S. Nonlinear pulse evolution in seeded free-electron laser amplifiers and in free-electron laser cascades. J. Appl. Phys. 98, 043110 (2005).

    ADS  Google Scholar 

  28. Bonifacio, R., De Salvo Souza, L., Pierini, P. & Piovella, N. The superradiant regime of a FEL: analytical and numerical results. Nucl. Instrum. Methods Phys. Res. A 296, 358–367 (1990).

    ADS  Google Scholar 

  29. Bonifacio, R., Piovella, N. & McNeil, B. W. J. Superradiant evolution of radiation pulses in a free-electron laser. Phys. Rev. A 44, R3441–R3444 (1991).

    ADS  Google Scholar 

  30. Yang, X., Mirian, N. & Giannessi, L. Postsaturation dynamics and superluminal propagation of a superradiant spike in a free-electron laser amplifier. Phys. Rev. Accel. Beams 23, 010703 (2020).

    ADS  Google Scholar 

  31. Watanabe, T. et al. Experimental characterization of superradiance in a single-pass high-gain laser-seeded free-electron laser amplifier. Phys. Rev. Lett. 98, 034802 (2007).

    ADS  Google Scholar 

  32. Giannessi, L. et al. High-order-harmonic generation and superradiance in a seeded free-electron laser. Phys. Rev. Lett. 108, 164801 (2012).

    ADS  Google Scholar 

  33. Giannessi, L. et al. Superradiant cascade in a seeded free-electron laser. Phys. Rev. Lett. 110, 044801 (2013).

    ADS  Google Scholar 

  34. Svelto, O. & Hanna, D. C. Principles of Lasers (Springer, 2010).

  35. Allaria, E., Ninno, G. D. & Spezzani, C. Experimental demonstration of frequency pulling in single-pass free-electron lasers. Opt. Express 19, 10619–10624 (2011).

    ADS  Google Scholar 

  36. Helml, W. et al. Ultrashort free-electron laser X-ray pulses. Appl. Sci. 7, 915 (2017).

    Google Scholar 

  37. Mitzner, R. et al. Direct autocorrelation of soft-x-ray free-electron-laser pulses by time-resolved two-photon double ionization of He. Phys. Rev. A 80, 025402 (2009).

    ADS  Google Scholar 

  38. Svetina, C. et al. The Low Density Matter (LDM) beamline at FERMI: optical layout and first commissioning. J. Synchrotron Radiat. 22, 538–543 (2015).

    Google Scholar 

  39. Zangrando, M. et al. Recent results of PADReS, the Photon Analysis Delivery and REduction System, from the FERMI FEL commissioning and user operations. J. Synchrotron Radiat. 22, 565–570 (2015).

    Google Scholar 

  40. Reiche, S. GENESIS 1.3: a fully 3D time-dependent FEL simulation code. Nucl. Instrum. Methods Phys. Res. A 429, 243–248 (1999).

    ADS  Google Scholar 

  41. Labat, M. et al. Pulse splitting in short wavelength seeded free electron lasers. Phys. Rev. Lett. 103, 264801 (2009).

    ADS  Google Scholar 

  42. De Ninno, G., Mahieu, B., Allaria, E., Giannessi, L. & Spampinati, S. Chirped seeded free-electron lasers: self-standing light sources for two-color pump-probe experiments. Phys. Rev. Lett. 110, 064801 (2013).

    ADS  Google Scholar 

  43. Mahieu, B. et al. Two-colour generation in a chirped seeded free-electron laser: a close look. Opt. Express 21, 22728–22741 (2013).

    ADS  Google Scholar 

  44. Bonifacio, R., Pellegrini, C. & Narducci, L. M. Collective instabilities and high-gain regime in a free electron laser. Opt. Commun. 50, 373–378 (1984).

    ADS  Google Scholar 

  45. Allaria, E. et al. Two-stage seeded soft-X-ray free-electron laser. Nat. Photonics 7, 913–918 (2013).

    ADS  Google Scholar 

  46. Henke, B. L., Gullikson, E. M. & Davis, J. C. X-ray interactions: photoabsorption, scattering, transmission, and reflection at E = 50–30,000 eV, Z = 1–92. At. Data Nucl. Data Tables 54, 181–342 (1993).

    ADS  Google Scholar 

  47. Düsterer, S. et al. Development of experimental techniques for the characterization of ultrashort photon pulses of extreme ultraviolet free-electron lasers. Phys. Rev. Spec. Top. Accel. Beams 17, 120702 (2014).

    ADS  Google Scholar 

  48. Roling, S. & Zacharias, H. in Synchrotron Light Sources and Free-Electron Lasers (eds Jaeschke, E. et al.) 891–925 (Springer, 2014).

  49. Eland, J. H. D. et al. Complete two-electron spectra in double photoionization: the rare gases Ar, Kr, and Xe. Phys. Rev. Lett. 90, 053003 (2003).

    ADS  Google Scholar 

  50. Squibb, R. J. et al. Acetylacetone photodynamics at a seeded free-electron laser. Nat. Commun. 9, 63 (2018).

    ADS  Google Scholar 

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We acknowledge S. Reiche for helpful discussions on bandwidth issues in the simulation of a multistage cascade in GENESIS 1.3. We are also grateful to the whole FERMI team for the dedicated work and support during this experiment.

Author information

Authors and Affiliations



N.S.M., S.S. and L.G. conceived the idea of the experiment. C.C. and T.M. conceived the ATI autocorrelation measurement scheme. N.S.M., S.S., E.A., L.B., G.D.N., S.D.M., G.P., P.R., C.S., G.G., M.T., X.Y. and L.G. contributed to the machine operation and tuning for the experiment. S.S., N.S.M. and F.S. simulated the FEL SRC dynamics in the experimental conditions. S.S. and F.S. investigated the energy detuning and the frequency-pulling effect. M.B.D. and A.D. tuned the seed laser for short-pulse operation. N.M., M.M., L.R. and M.Z. designed, aligned and operated the split-and-delay line; O.P., K.C.P., T.M., M.D.F., R.J.S. and C.C. operated the magnetic bottle electron spectrometer, acquired and analysed the cross-correlation data. T.M. and M.D.F. developed the analysis tools used during beam time. N.S.M., C.C., K.C.P. and L.G. wrote the manuscript, which was discussed and agreed by all the coauthors.

Corresponding author

Correspondence to Luca Giannessi.

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The authors declare no competing interests.

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Peer review informationNature Photonics thanks Agostino Marinelli and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–4, Discussion and references.

Source data

Source Data Fig. 2

Data file after analysis for Fig. 2.

Source Data Fig. 3

Data file after analysis for Fig. 3.

Source Data Fig. 4

Data file after analysis for Fig. 4.

Source Data Fig. 5

Zip file containing 7 + 7 HDF5 datasets of acquisitions of the FEL+linac parameters in SRC and HGHG configurations (Fig. 5a and Fig. 5b). Each file corresponds to a different tuning of the resonance in the final amplifier in the two configurations, SRC (Fig. 5a) and HGHG (Fig. 5b). The spectral raw data, to be averaged to prepare the figures, are in the folder /real time/spectrometer PRESTO/GetSpectrum. Each HDF5 file contains all the linac/undulator/beam data from a machine snapshot taken before the acquisition.

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Mirian, N.S., Di Fraia, M., Spampinati, S. et al. Generation and measurement of intense few-femtosecond superradiant extreme-ultraviolet free-electron laser pulses. Nat. Photon. 15, 523–529 (2021).

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