High-harmonic generation driven by femtosecond lasers makes it possible to capture the fastest dynamics in molecules and materials. However, thus far, the shortest isolated attosecond pulses have only been produced with linear polarization, which limits the range of physics that can be explored. Here, we demonstrate robust polarization control of isolated extreme-ultraviolet pulses by exploiting non-collinear high-harmonic generation driven by two counter-rotating few-cycle laser beams. The circularly polarized supercontinuum is produced at a central photon energy of 33 eV with a transform limit of 190 as and a predicted linear chirp of 330 as. By adjusting the ellipticity of the two counter-rotating driving pulses simultaneously, we control the polarization state of isolated extreme-ultraviolet pulses—from circular through elliptical to linear polarization—without sacrificing conversion efficiency. Access to the purely circularly polarized supercontinuum, combined with full helicity and ellipticity control, paves the way towards attosecond metrology of circular dichroism.

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The experimental work was carried out at National Tsing Hua University, Institute of Photonics Technologies, supported by the Ministry of Science and Technology, Taiwan (grants 105-2112-M-007-030-MY3, 105-2112-M-001-030 and 104-2112-M-007-012-MY3). The concept of isolated circularly polarized attosecond pulses was developed by C.H.-G., D.D.H., M.M.M., C.G.D., H.C.K., A.B. and A.J.-B.. C.H.-G. acknowledges support from the Marie Curie International Outgoing Fellowship within the EU Seventh Framework Programme for Research and Technological Development (2007–2013), under Research Executive Agency grant agreement no. 328334. C.H.-G. and L.P. acknowledge support from Junta de Castilla y León (SA046U16) and the Ministerio de Economía y Competitividad (FIS2013-44174-P, FIS2016-75652-P). C.H.-G. acknowledges support from a 2017 Leonardo Grant for Researchers and Cultural Creators (BBVA Foundation). M.M.M. and H.C.K. acknowledge support from the Department of Energy Basic Energy Sciences (award no. DE-FG02-99ER14982) for the concepts and experimental set-up. For part of the theory, A.B., A.J.-B., C.G.D., M.M.M. and H.C.K. acknowledge support from a Multidisciplinary University Research Initiatives grant from the Air Force Office of Scientific Research (award no. FA9550-16-1-0121). A.J.-B. also acknowledges support from the US National Science Foundation (grant no. PHY-1734006). This work utilized the Janus supercomputer, which is supported by the US National Science Foundation (grant no. CNS-0821794) and the University of Colorado, Boulder. This research made use of the high-performance computing resources of the Castilla y León Supercomputing Center (SCAYLE, www.scayle.es), financed by the European Regional Development Fund (ERDF). J.L.E. acknowledges support from the National Science Foundation Graduate Research Fellowship (DGE-1144083). L.R. acknowledges support from the Ministerio de Educación, Cultura y Deporte (FPU16/02591).

Author information


  1. Institute of Photonics Technologies, National Tsing Hua University, Hsinchu, Taiwan

    • Pei-Chi Huang
    • , Jen-Ting Huang
    • , Po-Yao Huang
    • , Chih-Hsuan Lu
    • , Shang-Da Yang
    • , A. H. Kung
    •  & Ming-Chang Chen
  2. Institute of Atomic and Molecular Sciences, Academica Sinica, Taipei, Taiwan

    • Pei-Chi Huang
    • , Chih-Hsuan Lu
    •  & A. H. Kung
  3. Grupo de Investigación en Aplicaciones del Láser y Fotónica, Departamento de Física Aplicada, University of Salamanca, Salamanca, Spain

    • Carlos Hernández-García
    • , Laura Rego
    •  & Luis Plaja
  4. JILA – Department of Physics, University of Colorado and NIST, Boulder, CO, USA

    • Daniel D. Hickstein
    • , Jennifer L. Ellis
    • , Agnieszka Jaron-Becker
    • , Andreas Becker
    • , Henry C. Kapteyn
    •  & Margaret M. Murnane
  5. Department of Physics, Colorado School of Mines, Golden, CO, USA

    • Charles G. Durfee
  6. Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

    • Ming-Chang Chen


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P.-C.H., J.-T.H., P.-Y.H., C.-H.L., D.D.H., J.L.E., C.G.D., H.C.K., M.M.M., A.H.K. and M.-C.C. designed the experiment with circularly polarized isolated high-harmonic pulses. P.-C.H., J.-T.H., P.-Y.H., S.-D.Y., A.H.K. and M.-C.C. proposed the full polarization control of HHG and designed the EUV polarimeter. P.-C.H., J.-T.H., P.-Y.H., C.-H.L. and M.-C.C. performed the experiments. C.H.-G., A.B. and A.J.-B. performed the theoretical simulations on circularly polarized isolated attosecond pulses. C.H.-G., L.R. and L.P. worked on the theoretical methods and simulations of the full polarization control of HHG. P.-C.H., C.H.-G., J.-T.H., P.-Y.H., L.R., L.P. and M.-C.C. analysed data. P.-C.H., C.H.-G., L.P., M.M.M. and M.-C.C. wrote the manuscript, to which all authors suggested improvement.

Competing interests

The authors declare no competing interests.

Corresponding authors

Correspondence to Pei-Chi Huang or Ming-Chang Chen.

Supplementary information

  1. Supplementary Information

    Supplementary notes, figures and table

  2. Supplementary Video 1

    Interference patterns of circularly polarized extreme-ultraviolet pulses versus time delays.

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