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.

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

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).

Laserdiodepolarization

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).

S-polarization vs p-polarization

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

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

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

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

Alberto A. Lutman, James P. MacArthur, Markus Ilchen, Ryan N. Coffee, Georgi L. Dakovski, Yuantao Ding, Hermann A. Dürr, Nick Hartmann, Daniel Higley, Konstantin Hirsch, Yurii I. Levashov, Agostino Marinelli, Tim Maxwell, Ankush Mitra, Stefan Moeller, Timur Osipov, Franz Peters, William F. Schlotter, Zachary R. Wolf, Zhirong Huang & Heinz-Dieter Nuhn

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

Linearly polarized light

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).

P-polarized light

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

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).

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).

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).

Linearpolarization

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.

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

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).

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).

Laser polarizationapp

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).

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

Lutman, A., MacArthur, J., Ilchen, M. et al. Polarization control in an X-ray free-electron laser. Nature Photon 10, 468–472 (2016). https://doi.org/10.1038/nphoton.2016.79

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

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

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

Unpolarizedlaser

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

Circularpolarization

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

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

Stanford Institute for Materials and Energy Sciences (SIMES), SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, 94025, California, USA

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.

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).

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

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).

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).

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