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 X-ray free-electron laser emitting in the sub-ångström region


The free-electron laser, first proposed by Madey1 in 1971, has significantly reduced laser wavelengths to the vacuum ultraviolet2,3 and soft X-ray regions4. Recently, an X-ray free-electron laser (XFEL) was operated at 1.2 Å at the Linac Coherent Light Source (LCLS)5. Here, we report the successful generation of sub-ångström laser light using a compact XFEL source, combining a short-period undulator with an 8 GeV electron beam. The shortest wavelength attained—0.634 Å (63.4 pm)—is four orders of magnitude smaller than the 694 nm generated by Maiman's first laser6. The maximum power exceeded 10 GW with a pulse duration of 10−14 s. This achievement will contribute to the widespread use of XFEL sources and provide broad opportunities for exploring new fields in science.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Schematic of SACLA.
Figure 2: Spectra comparison.
Figure 3: Intensity evolution along the undulator.
Figure 4: Intensity versus photon energy.


  1. Madey, J. J. M. Stimulated emission of bremsstrahlung in a periodic magnetic field. J. Appl. Phys. 42, 1906–1913 (1971).

    Article  ADS  Google Scholar 

  2. Ayvazyan, V. et al. Generation of GW radiation pulses from a VUV free-electron laser operating in the femtosecond regime. Phys. Rev. Lett. 88, 104802 (2002).

    Article  ADS  Google Scholar 

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

    Article  Google Scholar 

  4. Ackermann, W. et al. Operation of a free-electron laser from the extreme ultraviolet to the water window. Nature Photon. 1, 336–342 (2007).

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  6. Maiman, T. H. Stimulated optical radiation in ruby. Nature 187, 493–494 (1960).

    Article  ADS  Google Scholar 

  7. MacGowan, B. J. et al. Short wavelength X-ray laser research at the Lawrence Livermore National Laboratory. Phys. Fluids B 4, 2326–2337 (1992).

    Article  ADS  Google Scholar 

  8. Spielmann, C. et al. Generation of coherent X-rays in the water window using 5-femtosecond laser pulses. Science 278, 661–664 (1997).

    Article  ADS  Google Scholar 

  9. Takahashi, E. J. et al. Coherent water window X ray by phase-matched high-order harmonic generation in neutral media. Phys. Rev. Lett. 101, 253901 (2008).

    Article  ADS  Google Scholar 

  10. Seres J. et al. Source of coherent kiloelectronvolt X-rays. Nature 433, 596 (2005).

    Article  ADS  Google Scholar 

  11. Elias, L. R., Fairbank, W. M., Madey, J. M. J., Schwettman, H. A. & Smith, T. I. Observation of stimulated emission of radiation by relativistic electrons in a spatially periodic transverse magnetic field. Phys. Rev. Lett. 36, 717–720 (1976).

    Article  ADS  Google Scholar 

  12. 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 

  13. Bonifacio, R., Pellegrini, C. & Narducci, L. M. Collective instabilities and high-gain regime in a free-electron laser. Opt. Commun. 50, 373–377 (1984).

    Article  ADS  Google Scholar 

  14. Milton, S. V. et al. Exponential gain and saturation of a self-amplified spontaneous emission free-electron laser. Science 292, 2037–2041 (2001).

    Article  ADS  Google Scholar 

  15. Altarelli, M. et al. (eds) XFEL: the European X-Ray Free-Electron Laser, Technical Design Report, Preprint DESY 2006-097 (DESY Hamburg, 2006).

    Google Scholar 

  16. Altarelli, M. The European X-ray Free-Electron Laser Facility in Hamburg. Nucl. Instrum. Methods B269, 2845–2849 (2011).

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  18. Huang, Z. & Kim, K. J. Review of X-ray free-electron laser theory. Phys. Rev. ST Accel. Beams 10, 034801 (2007).

    Article  ADS  Google Scholar 

  19. Shintake, T., Matsumoto, H., Ishikawa, T. & Kitamura, H. SPring-8 Compact SASE Source (SCSS). Proc. SPIE 4500, 12–23 (2001).

    Article  ADS  Google Scholar 

  20. Tanaka, T. & Shintake, T. (eds) SCSS X-FEL Conceptual Design Report (RIKEN Harima Institute, 2005).

    Google Scholar 

  21. Kitamura, H. Recent trends of insertion-device technology for X-ray sources. J. Synchrotron Rad. 7, 121–130 (2000).

    Article  Google Scholar 

  22. Togawa, K. et al. CeB6 electron gun for low-emittance injector. Phys. Rev. ST Accel. Beams 10, 020703 (2007).

    Article  ADS  Google Scholar 

  23. Togawa, K., Hara, T. & Tanaka, H. Electron bunch compression using an over-correction method for a compact X-ray free-electron laser. Phys. Rev. ST Accel. Beams 12, 080706 (2009).

    Article  ADS  Google Scholar 

  24. Nuhn, H. D. et al. Characterization of second harmonic afterburner radiation at the LCLS. Proc. FEL 2010, 690–695 (2010).

  25. Saldin, E. L., Schneidmiller, E. A. & Yurkov, M. V. (eds) in The Physics of Free Electron Lasers Ch. 6 (Springer, 1999).

    Google Scholar 

  26. Tanaka, T. FEL simulation code for undulator performance estimation. Proc. FEL 2004, 435–438 (2004).

  27. Ego, H. et al. Transverse C-band deflecting structure for longitudinal phase space diagnostics in the XFEL/SPring-8 ‘SACLA’. Proc. IPAC 2011, 1221–1223 (2011).

  28. Kim, K. J. An analysis of self-amplified spontaneous emission. Nucl. Instrum. Methods A250, 396–403 (1986).

    Article  ADS  Google Scholar 

  29. Hara, T. et al. Cryogenic permanent magnet undulators. Phys. Rev. ST Accel. Beams 7, 050702 (2004).

    Article  ADS  Google Scholar 

  30. Tono, K. et al. Single-shot beam-position monitor for X-ray free electron laser. Rev. Sci. Instrum. 82, 023108 (2011).

    Article  ADS  Google Scholar 

Download references


The authors thank the staff of SACLA/SPring-8 for their continuous support and M.E. Couprie for fruitful discussions. The authors also thank H. Matsumoto and H. Baba for developing the basic components of the C-band accelerator system.

Author information

Authors and Affiliations



All authors contributed to the design and construction of SACLA, and to conducting the experiments. T.I., H.K. and T.S. proposed a concept for the compact XFEL source. N.K. supervised the construction project for SACLA. H.T., T.H., K.T., T.T. and M.Y. summarized the strategy for the beam commissioning, and led experiments and data analyses.

Corresponding authors

Correspondence to Hitoshi Tanaka or Makina Yabashi.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

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

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


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