Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

A compact and cost-effective hard X-ray free-electron laser driven by a high-brightness and low-energy electron beam


We present the first lasing results of SwissFEL, a hard X-ray free-electron laser (FEL) that recently came into operation at the Paul Scherrer Institute in Switzerland. SwissFEL is a very stable, compact and cost-effective X-ray FEL facility driven by a low-energy and ultra-low-emittance electron beam travelling through short-period undulators. It delivers stable hard X-ray FEL radiation at 1-Å wavelength with pulse energies of more than 500 μJ, pulse durations of ~30 fs (root mean square) and spectral bandwidth below the per-mil level. Using special configurations, we have produced pulses shorter than 1 fs and, in a different set-up, broadband radiation with an unprecedented bandwidth of ~2%. The extremely small emittance demonstrated at SwissFEL paves the way for even more compact and affordable hard X-ray FELs, potentially boosting the number of facilities worldwide and thereby expanding the population of the scientific community that has access to X-ray FEL radiation.

This is a preview of subscription content

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Schematic of SwissFEL.
Fig. 2: Electron and photon beam properties at SwissFEL.
Fig. 3: Transient response in Bi(111) peak intensity displaying a coherent optical phonon, displacively excited by an 800-nm pulse.
Fig. 4: SwissFEL special operation modes.

Data availability

The data that support the figures in this paper and other findings of this study are available from the corresponding author upon reasonable request.

Code availability

The FEL code Genesis 1.3 is available at


  1. 1.

    McNeil, B. W. J. & Thompson, N. R. X-ray free-electron lasers. Nat. Photon. 4, 814–821 (2010).

    ADS  Google Scholar 

  2. 2.

    Pellegrini, C., Marinelli, A. & Reiche, S. The physics of X-ray free-electron lasers. Rev. Mod. Phys. 88, 015006 (2016).

    ADS  Google Scholar 

  3. 3.

    Bostedt, C. et al. Linac Coherent Light Source: the first five years. Rev. Mod. Phys. 88, 015007 (2016).

    ADS  Google Scholar 

  4. 4.

    Kern, J. et al. Simultaneous femtosecond X-ray spectroscopy and diffraction of photosystem II at room temperature. Science 340, 491–495 (2013).

    ADS  Google Scholar 

  5. 5.

    Nango, E. et al. A three-dimensional movie of structural changes in bacteriorhodopsin. Science 354, 1552–1557 (2016).

    ADS  Google Scholar 

  6. 6.

    Nogly, P. et al. Retinal isomerization in bacteriorhodopsin captured by a femtosecond X-ray laser. Science 361, eaat0094 (2018).

    Google Scholar 

  7. 7.

    Dell’Angela, M. et al. Real-time observation of surface bond breaking with an X-ray laser. Science 339, 1302–1305 (2013).

    ADS  Google Scholar 

  8. 8.

    Öström, H. et al. Probing the transition state region in catalytic CO oxidation on Ru. Science 347, 978–982 (2015).

    ADS  Google Scholar 

  9. 9.

    Graves, C. E. et al. Nanoscale spin reversal by non-local angular momentum transfer following ultrafast laser excitation in ferrimagnetic GdFeCo. Nat. Mater. 12, 293–298 (2013).

    ADS  Google Scholar 

  10. 10.

    Beaud, P. et al. A time-dependent order parameter for ultrafast photoinduced phase transitions. Nat. Mater. 13, 923–927 (2014).

    ADS  Google Scholar 

  11. 11.

    Dornes, C. et al. The ultrafast Einstein–de Haas effect. Nature 565, 209–212 (2019).

    ADS  Google Scholar 

  12. 12.

    Liu, W. et al. Serial femtosecond crystallography of G protein-coupled receptors. Science 342, 1521–1524 (2013).

    ADS  Google Scholar 

  13. 13.

    Redecke, L. et al. Natively inhibited Trypanosoma brucei cathepsin B structure determined by using an X-ray laser. Science 339, 227–230 (2012).

    ADS  Google Scholar 

  14. 14.

    Kang, Y. et al. Crystal structure of rhodopsin bound to arrestin by femtosecond X-ray laser. Nature 523, 561–567 (2015).

    ADS  Google Scholar 

  15. 15.

    Glover, T. E. et al. X-ray and optical wave mixing. Nature 488, 603–608 (2012).

    ADS  Google Scholar 

  16. 16.

    Tamasaku, K. et al. X-ray two-photon absorption competing against single and sequential multiphoton processes. Nat. Photon. 8, 313–316 (2014).

    ADS  Google Scholar 

  17. 17.

    Szlachetko, J. et al. Establishing nonlinearity thresholds with ultraintense X-ray pulses. Sci. Rep. 6, 33292 (2016).

    ADS  Google Scholar 

  18. 18.

    Kondratenko, A. M. & Saldin, E. L. Generation of coherent radiation by a relativistic electron beam in an ondulator. Part. Accel. 10, 207–216 (1980).

    Google Scholar 

  19. 19.

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

    Google Scholar 

  20. 20.

    Emma, P. et al. First lasing and operation of an ångström-wavelength free-electron laser. Nat. Photon. 4, 641–647 (2010).

    ADS  Google Scholar 

  21. 21.

    Ishikawa, T. et al. A compact X-ray free-electron laser emitting in the sub-ångström region. Nat. Photon. 6, 540–544 (2012).

    ADS  Google Scholar 

  22. 22.

    Kang, H.-S. et al. Hard X-ray free-electron laser with femtosecond-scale timing jitter. Nat. Photon. 11, 708–713 (2017).

    ADS  Google Scholar 

  23. 23.

    Decking, W. et al. A MHz-repetition-rate hard X-ray free-electron laser driven by a superconducting linear accelerator. Nat. Photon. 14, 391–397 (2020).

    ADS  Google Scholar 

  24. 24.

    Ganter, R. et al. SwissFEL Conceptual Design Report PSI Report 10-04 (Paul Scherrer Institut, 2012).

  25. 25.

    Shintake, T. et al. A compact free-electron laser for generating coherent radiation in the extreme ultraviolet region. Nat. Photon. 2, 555–559 (2008).

    Google Scholar 

  26. 26.

    Zennaro, R., Bopp, M., Citterio, A., Reiser, R. & Stapf, T. C-band RF pulse compressor for SwissFEL. In Proceedings of the 4th International Particle Accelerator Conference 2827–2829 (JACoW Publishing, 2013).

  27. 27.

    Raguin, J.-Y. & Bopp, M. The Swiss FEL C-band accelerating structure: RF design and thermal analysis. In Proceedings of LINAC 2012, 501–503 (JACoW Publishing, 2013).

  28. 28.

    Cartlidge, E. European XFEL to shine as brightest, fastest X-ray source. Science 354, 22–23 (2016).

    ADS  Google Scholar 

  29. 29.

    Fraser, J. S., Sheffield, R. L., Gray, E. R. & Rodenz, G. W. High-brightness photoemitier injector for electron accelerators. IEEE Trans. Nucl. Sci. 32, 1791–1793 (1985).

    ADS  Google Scholar 

  30. 30.

    Trisorio, A., Divall, M., Vicario, C., Hauri, C. P. & Courjaud, A. New concept for the SwissFEL gun laser. In Proceedings of FEL 2013, Vol. 35, 442–446 (JACoW Publishing, 2013).

  31. 31.

    Raguin, J.-Y., Bopp, M., Citterio, A. & Scherer, A. The Swiss FEL RF gun: RF design and thermal analysis. In Proceedings of 26th International Linear Accelerator Conference 2012, 442–444 (JACoW Publishing, 2013).

  32. 32.

    Roux, R. Conception of photoinjectors for the CTF3 experiment. Int. J. Mod. Phys. A 22, 3925–3941 (2007).

    ADS  Google Scholar 

  33. 33.

    Xiao, L. et al. Dual feed RF gun design for the LCLS. In Proceedings of the 2005 Particle Accelerator Conference 3432–3434 (IEEE, 2005).

  34. 34.

    Bettoni, S., Pedrozzi, M. & Reiche, S. Low emittance injector design for free electron lasers. Phys. Rev. ST Accel. Beams 18, 123403 (2015).

    ADS  Google Scholar 

  35. 35.

    Ferrario, M. et al. Direct measurement of the double emittance minimum in the beam dynamics of the sparc high-brightness photoinjector. Phys. Rev. Lett. 99, 234801 (2007).

    ADS  Google Scholar 

  36. 36.

    Dehler, M. et al. X-band rf structure with integrated alignment monitors. Phys. Rev. ST Accel. Beams 12, 062001 (2009).

    ADS  Google Scholar 

  37. 37.

    Dowell, D. H., Hayward, T. D. & Vetter, A. M. Magnetic pulse compression using a third harmonic RF linearizer. In Proceedings of the 1995 Particle Accelerator Conference 992–994 (IEEE, 1996).

  38. 38.

    Follath, R. et al. Optical design of the ARAMIS-beamlines at SwissFEL. In Proceedings of the 12th International Conference on Synchrotron Radiation Instrumentation, Vol. 1741, 020009 (AIP, 2016).

  39. 39.

    Erny, C. & Hauri, C. P. The SwissFEL experimental laser facility. J. Synchrotron Radiat. 23, 1143–1150 (2016).

    Google Scholar 

  40. 40.

    Redford, S. et al. Operation and performance of the JUNGFRAU photon detector during first FEL and synchrotron experiments. J. Instrum. 13, C11006 (2018).

    Google Scholar 

  41. 41.

    Milne, C. et al. Opportunities for chemistry at the SwissFEL X-ray free electron laser. CHIMIA Int. J. Chem. 71, 299–307 (2017).

    Google Scholar 

  42. 42.

    Chapman, H. N. et al. Femtosecond X-ray protein nanocrystallography. Nature 470, 73–77 (2011).

    ADS  Google Scholar 

  43. 43.

    Ingold, G. et al. Experimental station Bernina at SwissFEL: condensed matter physics on femtosecond time scales investigated by X-ray diffraction and spectroscopic methods. J. Synchrotron Radiat. 26, 874–886 (2019).

    Google Scholar 

  44. 44.

    Milne, C. J. et al. SwissFEL: the Swiss X-ray Free Electron Laser. Appl. Sci. 7, 720 (2017).

    Google Scholar 

  45. 45.

    Heifets, S., Stupakov, G. & Krinsky, S. Coherent synchrotron radiation instability in a bunch compressor. Phys. Rev. ST Accel. Beams 5, 064401 (2002).

    ADS  Google Scholar 

  46. 46.

    Prat, E., Bettoni, S., Braun, H.-H., Ganter, R. & Schietinger, T. Measurements of copper and cesium telluride cathodes in a radio-frequency photoinjector. Phys. Rev. ST Accel. Beams 18, 043401 (2015).

    ADS  Google Scholar 

  47. 47.

    Prat, E. et al. Emittance measurements and minimization at the SwissFEL injector test facility. Phys. Rev. ST Accel. Beams 17, 104401 (2014).

    ADS  Google Scholar 

  48. 48.

    Prat, E. et al. Generation and characterization of intense ultralow-emittance electron beams for compact X-ray free-electron lasers. Phys. Rev. Lett. 123, 234801 (2019).

    ADS  Google Scholar 

  49. 49.

    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 

  50. 50.

    Sokolowski-Tinten, K. et al. Femtosecond X-ray measurement of coherent lattice vibrations near the Lindemann stability limit. Nature 422, 287–289 (2003).

    ADS  Google Scholar 

  51. 51.

    Smolentsev, G. et al. Taking a snapshot of the triplet excited state of an OLED organometallic luminophore using X-rays. Nat. Commun. 11, 2131 (2020).

    ADS  Google Scholar 

  52. 52.

    Svetina, C. et al. Towards X-ray transient grating spectroscopy. Opt. Lett. 44, 574–577 (2019).

    Google Scholar 

  53. 53.

    Skopintsev, P. et al. Femtosecond-to-millisecond structural changes in a light-driven sodium pump. Nature 583, 314–318 (2020).

    ADS  Google Scholar 

  54. 54.

    Saldin, E. L., Schneidmiller, E. A. & Yurkov, M. V. Statistical properties of radiation from VUV and X-ray free electron laser. Opt. Commun. 148, 383–403 (1998).

    ADS  Google Scholar 

  55. 55.

    Ayvazyan, V. et al. Study of the statistical properties of the radiation from a VUV SASE FEL operating in the femtosecond regime. Nucl. Instrum. Methods Phys. Res. A 507, 368–372 (2003).

    ADS  Google Scholar 

  56. 56.

    Inubushi, Y. et al. Determination of the pulse duration of an X-ray free electron laser using highly resolved single-shot spectra. Phys. Rev. Lett. 109, 144801 (2012).

    ADS  Google Scholar 

  57. 57.

    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 

  58. 58.

    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 

  59. 59.

    Duris, J. et al. Tunable isolated attosecond X-ray pulses with gigawatt peak power from a free-electron laser. Nat. Photon. 14, 30–36 (2019).

    Google Scholar 

  60. 60.

    Patterson, B. D. et al. Coherent science at the SwissFEL X-ray laser. New J. Phys. 12, 035012 (2010).

    ADS  Google Scholar 

  61. 61.

    Prat, E., Dijkstal, P., Ferrari, E. & Reiche, S. Demonstration of large bandwidth hard X-ray free-electron laser pulses at SwissFEL. Phys. Rev. Lett. 124, 074801 (2020).

    ADS  Google Scholar 

  62. 62.

    Dijkstal, P., Malyzhenkov, A., Reiche, S. & Prat, E. Demonstration of two-color X-ray free-electron laser pulses with a sextupole magnet. Phys. Rev. Accel. Beams 23, 030703 (2020).

    ADS  Google Scholar 

  63. 63.

    Inoue, I. et al. Observation of femtosecond X-ray interactions with matter using an X-ray–X-ray pump–probe scheme. Proc. Natl Acad. Sci. USA 113, 1492–1497 (2016).

    ADS  Google Scholar 

  64. 64.

    Calvi, M. et al. A GdBCO bulk staggered array undulator. Supercond. Sci. Technol. 33, 014004 (2020).

    ADS  Google Scholar 

  65. 65.

    Prat, E., Bettoni, S. & Reiche, S. Enhanced X-ray free-electron-laser performance from tilted electron beams. Nucl. Instrum. Methods Phys. Res. A 865, 1–8 (2017).

    ADS  Google Scholar 

  66. 66.

    Lutman, A. A. et al. Fresh-slice multicolour X-ray free-electron lasers. Nat. Photon. 10, 745–750 (2016).

    ADS  Google Scholar 

  67. 67.

    Paraliev, M. et al. Commissioning and stability studies of the SwissFEL bunch-separation system. In Proceedings of the 2009 Free Electron Laser Conference 404–407 (JACoW Publishing, 2019).

  68. 68.

    Schmidt, T. & Calvi, M. APPLE X undulator for the SwissFEL soft X-ray beamline athos. Synchrotron Radiat. News 31, 35–40 (2018).

    Google Scholar 

  69. 69.

    Abela, R. et al. The SwissFEL soft X-ray free-electron laser beamline: Athos. J. Synchrotron Radiat. 26, 1073–1084 (2019).

    Google Scholar 

  70. 70.

    Harmand, M. et al. Achieving few-femtosecond time-sorting at hard X-ray free-electron lasers. Nat. Photon. 7, 215–218 (2013).

    ADS  Google Scholar 

  71. 71.

    Guetg, M. W., Beutner, B., Prat, E. & Reiche, S. Optimization of free electron laser performance by dispersion-based beam-tilt correction. Phys. Rev. ST Accel. Beams 18, 030701 (2015).

    ADS  Google Scholar 

  72. 72.

    Aiba, M. & Böge, M. Beam-based alignment of an X-FEL undulator section utilizing the corrector pattern. In Proceedings of the 2012 Free Electron Laser Conference 293–296 (JACoW Publishing, 2013).

  73. 73.

    Emma, P., Carr, R. & Nuhn, H.-D. Beam-based alignment for the LCLS FEL undulator. Nucl. Instrum. Methods Phys. Res. A 429, 407–413 (1999).

    ADS  Google Scholar 

  74. 74.

    Calvi, M. et al. General strategy for the commissioning of the ARAMIS undulators with a 3-GeV electron beam. In Proceedings of the 2014 Free Electron Laser Conference 107–110 (JACoW Publishing, 2015).

  75. 75.

    Prat, E. Symmetric single-quadrupole-magnet scan method to measure the 2D transverse beam parameters. Nucl. Instrum. Methods Phys. Res. A 743, 103–108 (2014).

    ADS  Google Scholar 

  76. 76.

    Ischebeck, R., Prat, E., Thominet, V. & Ozkan Loch, C. Transverse profile imager for ultrabright electron beams. Phys. Rev. ST Accel. Beams 18, 082802 (2015).

    ADS  Google Scholar 

  77. 77.

    Orlandi, G. L. et al. Design and experimental tests of free electron laser wire scanners. Phys. Rev. Accel. Beams 19, 092802 (2016).

    ADS  Google Scholar 

  78. 78.

    Orlandi, G. et al. Bunch length and energy measurements in the bunch compressor of a free-electron laser. Phys. Rev. Accel. Beams 22, 072803 (2019).

    ADS  Google Scholar 

  79. 79.

    Craievich, P., Ischebeck, R., Löhl, F., Orlandi, G. L. & Prat, E. Transverse deflecting structures for bunch length and slice emittance measurements on SwissFEL. In Proceedings of the 2013 Free Electron Laser Conference 236–241 (JACoW Publishing, 2013).

  80. 80.

    Keil, B. et al. First beam commissioning experience with the SwissFEL Cavity BPM system. In Proceedings of the 2017 International Beam Instrumentation Conference 251–254 (JACoW Publishing, 2017).

  81. 81.

    Frei, F. et al. Development of electron bunch compression monitors for SwissFEL. In Proceedings of the 2013 International Beam Instrumentation Conference 769–771 (JACoW Publishing, 2013).

  82. 82.

    Arsov, V. et al. First results from the bunch arrival-time monitors at SwissFEL. In Proceedings of the 2018 International Beam Instrumentation Conference 420–424 (JACoW Publishing, 2019).

  83. 83.

    Juranić, P. et al. SwissFEL Aramis beamline photon diagnostics. J. Synchrotron Radiat. 25, 1238–1248 (2018).

    Google Scholar 

Download references


We thank all the technical groups involved in the construction, installation and operation of SwissFEL. We also thank K. Sokolowski Tinten and M. Horn-von Hoegen for providing the thin-film Bi samples used in the timing characterization. This work has been supported by SNF grant no. 200021 175498 and no. 51NF40-183615 (NCCR:MUST). Moreover, this project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 695197 DYNAMOX).

Author information




E.P. wrote the initial version of the manuscript with the help of P.J., R.I., H.T.L., F.L., C.J.M., S. Reiche, T. Schietinger and H.-H.B. All authors contributed to the final version of the document. All authors participated in the design, construction or commissioning of SwissFEL. F.L. was the machine coordinator of SwissFEL. H.-H.B., R.A. and L.P. were the project leaders of SwissFEL.

Corresponding author

Correspondence to Eduard Prat.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Prat, E., Abela, R., Aiba, M. et al. A compact and cost-effective hard X-ray free-electron laser driven by a high-brightness and low-energy electron beam. Nat. Photonics 14, 748–754 (2020).

Download citation

Further reading


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing