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.

Polarization control in an X-ray free-electron laser


X-ray free-electron lasers are unique sources of high-brightness coherent radiation. However, existing devices supply only linearly polarized light, precluding studies of chiral dynamics. A device called the Delta undulator has been installed at the Linac Coherent Light Source (LCLS) to provide tunable polarization. With a reverse tapered planar undulator line to pre-microbunch the beam and the novel technique of beam diverting, hundreds of microjoules of circularly polarized X-ray pulses are produced at 500–1,200 eV. These X-ray pulses are tens of femtoseconds long, have a degree of circular polarization of 0.98–0.04+0.02 at 707 eV and may be scanned in energy. We also present a new two-colour X-ray pump–X-ray probe operating mode for the LCLS. Energy differences of ΔE/E = 2.4% are supported, and the second pulse can be adjusted to any elliptical polarization. In this mode, the pointing, timing, intensity and wavelength of the two pulses can be modified.

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: Reverse taper and beam diverting.
Figure 2: X-ray profiles in the diverted-beam scheme.
Figure 3: Circular polarization performance at 707 eV.
Figure 4: Two-colour, two-polarization scheme.
Figure 5: Two-colour, two-polarization experimental demonstration.


  1. Schütz, G. et al. Absorption of circularly polarized X rays in iron. Phys. Rev. Lett. 58, 737–740 (1987).

    ADS  Article  Google Scholar 

  2. Hergenhahn, U. et al. Photoelectron circular dichroism in core level ionization of randomly oriented pure enantiomers of the chiral molecule camphor. J. Chem. Phys. 120, 4553–4556 (2004).

    ADS  Article  Google Scholar 

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

    ADS  Article  Google Scholar 

  4. Nguyen, L. A., He, H. & Pham-Huy, C. Chiral drugs: an overview. Int. J. Biomed. Sci. 2, 85–100 (2006).

    Google Scholar 

  5. Böwering, N. et al. Asymmetry in photoelectron emission from chiral molecules induced by circularly polarized light. Phys. Rev. Lett. 86, 1187–1190 (2001).

    ADS  Article  Google Scholar 

  6. von Korff Schmising, C. et al. Imaging ultrafast demagnetization dynamics after a spatially localized optical excitation. Phys. Rev. Lett. 112, 217203 (2014).

    ADS  Article  Google Scholar 

  7. Rohringer, N. et al. Atomic inner-shell X-ray laser at 1.46 nanometres pumped by an X-ray free-electron laser. Nature 481, 488–491 (2012).

    ADS  Article  Google Scholar 

  8. Stöhr, J. & Siegmann, H. Magnetism: From Fundamentals to Nanoscale Dynamics (Springer Series in Solid-State Sciences, Springer, 2006).

    Google Scholar 

  9. Elleaume, P. Generation of various polarization states from insertion devices: a review. Rev. Sci. Instrum. 60, 1830–1833 (1989).

    ADS  Article  Google Scholar 

  10. Chen, C. T., Sette, F., Ma, Y. & Modesti, S. Soft-X-ray magnetic circular dichroism at the l2,3 edges of nickel. Phys. Rev. B 42, 7262–7265 (1990).

    ADS  Article  Google Scholar 

  11. Sasaki, S., Shimada, T., ichi Yanagida, K., Kobayashi, H. & Miyahara, Y. First observation of undulator radiation from apple-1. Nucl. Instrum. Methods A 347, 87–91 (1994).

    ADS  Article  Google Scholar 

  12. Popmintchev, T. et al. Bright coherent ultrahigh harmonics in the keV X-ray regime from mid-infrared femtosecond lasers. Science 336, 1287–1291 (2012).

    ADS  MathSciNet  Article  Google Scholar 

  13. Vodungbo, B. et al. Polarization control of high order harmonics in the EUV photon energy range. Opt. Express 19, 4346–4356 (2011).

    ADS  Article  Google Scholar 

  14. Litvinenko, V. N. et al. The OK-5/Duke storage ring VUV FEL with variable polarization. Nucl. Instrum. Methods A 475, 407–416 (2001).

    ADS  Article  Google Scholar 

  15. Allaria, E. et al. Highly coherent and stable pulses from the Fermi seeded free-electron laser in the extreme ultraviolet. Nature Photon. 6, 699–704 (2012).

    ADS  Article  Google Scholar 

  16. Allaria, E. et al. Two-stage seeded soft-X-ray free-electron laser. Nature Photon. 7, 913–918 (2013).

    ADS  Article  Google Scholar 

  17. Allaria, E. et al. The FERMI free-electron lasers. J. Synchrotron Radiat. 22, 485–491 (2015).

    Article  Google Scholar 

  18. Pfau, B. et al. Magnetic imaging at linearly polarized X-ray sources. Opt. Express 18, 13608–13615 (2010).

    ADS  Article  Google Scholar 

  19. Wang, T. et al. Femtosecond single-shot imaging of nanoscale ferromagnetic order in Co/Pd multilayers using resonant X-ray holography. Phys. Rev. Lett. 108, 267403 (2012).

    ADS  Article  Google Scholar 

  20. Emma, P. et al. First lasing and operation of an angstrom-wavelength free-electron laser. Nature Photon. 4, 641–647 (2009).

    ADS  Article  Google Scholar 

  21. Nuhn, H.-D. et al. in Proc. 35th Int. Free Electron Laser Conf. (FEL2013) 348–350 (Curran Associates, 2014).

  22. Temnykh, A. B. Delta undulator for Cornell Energy Recovery LINAC. Phys. Rev. ST Accel. Beams 11, 120702 (2008).

    ADS  Article  Google Scholar 

  23. Schneidmiller, E. A. & Yurkov, M. V. Obtaining high degree of circular polarization at X-ray free electron lasers via a reverse undulator taper. Phys. Rev. ST Accel. Beams 16, 110702 (2013).

    ADS  Article  Google Scholar 

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

    ADS  Article  Google Scholar 

  25. Lutman, A. A. et al. Experimental demonstration of femtosecond two-color X-ray free-electron lasers. Phys. Rev. Lett. 110, 134801 (2013).

    ADS  Article  Google Scholar 

  26. Marinelli, A. et al. Multicolor operation and spectral control in a gain-modulated X-ray free-electron laser. Phys. Rev. Lett. 111, 134801 (2013).

    ADS  Article  Google Scholar 

  27. Ratner, D. et al. Experimental demonstration of a soft X-ray self-seeded free-electron laser. Phys. Rev. Lett. 114, 054801 (2015).

    ADS  Article  Google Scholar 

  28. Amman, J. et al. Demonstration of self-seeding in a hard-X-ray free-electron laser. Nature Photon. 6, 693–698 (2012).

    ADS  Article  Google Scholar 

  29. Lutman, A. A. et al. Demonstration of single-crystal self-seeded two-color X-ray free-electron lasers. Phys. Rev. Lett. 113, 254801 (2014).

    ADS  Article  Google Scholar 

  30. Kim, K. J. A synchrotron radiation source with arbitrarily adjustable elliptical polarization. Nucl. Instrum. Methods 219, 425–429 (1984).

    Article  Google Scholar 

  31. Deng, H. et al. Polarization switching demonstration using crossed-planar undulators in a seeded free-electron laser. Phys. Rev. ST Accel. Beams 17, 020704 (2014).

    ADS  Article  Google Scholar 

  32. Ferrari, E. et al. Single shot polarization characterization of XUV FEL pulses from crossed polarized undulators. Sci. Rep. 5, 13531 (2015).

    ADS  Article  Google Scholar 

  33. Ding, Y. & Huang, Z. Statistical analysis of crossed undulator for polarization control in a self-amplified spontaneous emission free electron laser. Phys. Rev. ST Accel. Beams 11, 030702 (2008).

    ADS  Article  Google Scholar 

  34. Allaria, E. et al. Control of the polarization of a vacuum-ultraviolet, high-gain, free-electron laser. Phys. Rev. X 4, 041040 (2014).

    Google Scholar 

  35. Hartmann, G. et al. Circular dichroism measurements at an X-ray free-electron laser with polarization control. Preprint manuscript no. SLAC-PUB-16514 (SLAC-PUB, 2016).

  36. Higley, D. J. et al. Femtosecond X-ray magnetic circular dichroism absorption spectroscopy at an X-ray free electron laser. Rev. Sci. Instrum. 87, 033110 (2016).

    ADS  Article  Google Scholar 

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

    ADS  Article  Google Scholar 

  38. Marinelli, A. et al. High-intensity double-pulse X-ray free-electron laser. Nature Commun. 6, 6369 (2015).

    ADS  Article  Google Scholar 

Download references


The authors thank C.P. O'Grady for the online data-handling system. This work was supported by Department of Energy contract no. DE-AC02-76SF00515. A.O.L. acknowledges funding from the Knut and Alice Wallenberg Foundation through the Max IV synchrotron radiation facility programme. K.H. thanks the AvH Foundation for financial support through the Feodor-Lynen programme. M.I. acknowledges funding from the Volkswagen Foundation within a Peter Paul Ewald-Fellowship.

Author information

Authors and Affiliations



A.A.L., J.P.M., M.I., A.O.L., Z.H. and H.-D.N. co-wrote the manuscript. A.A.L. conceived the beam-diverting and two-colour, two-polarization schemes. J.P.M., A.Ma., Y.D. and Z.H. provided modelling and theoretical support for the reverse taper and beam-diverting techniques. A.A.L., J.P.M., Y.D., A.Ma., T.M., F.P., Z.R.W., Z.H. and H.-D.N. configured the LCLS and the Delta for photon beam generation during the experiments. M.I., A.O.L., J.B., R.N.C., L.D., L.G., J.G., G.H., N.H., S.M., A.Mi, T.O., M.P., I.S., F.S., J.S., J.V. and P.W. prepared the online diagnostic experiments with the TOF polarimeter. M.I., A.O.L., J.B., R.N.C., L.D., J.G., G.H., N.H., S.M., T.O., M.P., F.S., I.S., J.S., J.V. and P.W. performed the experiments with the TOF polarimeter, and A.O.L., M.I., G.H. and J.B. analysed the data offline. A.O.L. provided online data analysis. D.H., G.L.D., H.A.D., K.H. and W.F.S. measured the photon beam with the XMCD technique, and D.H. and K.H. analysed the data. F.P. designed the Delta built at SLAC. Z.R.W. and Y.I.L. measured and tuned the Delta before installation. H.-D.N. is the Delta undulator project lead.

Corresponding author

Correspondence to Alberto A. Lutman.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Lutman, A., MacArthur, J., Ilchen, M. et al. Polarization control in an X-ray free-electron laser. Nature Photon 10, 468–472 (2016).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

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