Coherent control with a short-wavelength free-electron laser

Journal name:
Nature Photonics
Year published:
Published online

Extreme ultraviolet and X-ray free-electron lasers (FELs) produce short-wavelength pulses with high intensity, ultrashort duration, well-defined polarization and transverse coherence, and have been utilized for many experiments previously possible only at long wavelengths: multiphoton ionization1, pumping an atomic laser2 and four-wave mixing spectroscopy3. However one important optical technique, coherent control, has not yet been demonstrated, because self-amplified spontaneous emission FELs have limited longitudinal coherence4, 5, 6, 7. Single-colour pulses from the FERMI seeded FEL are longitudinally coherent8, 9, and two-colour emission is predicted to be coherent. Here, we demonstrate the phase correlation of two colours, and manipulate it to control an experiment. Light of wavelengths 63.0 and 31.5 nm ionized neon, and we controlled the asymmetry of the photoelectron angular distribution10, 11 by adjusting the phase, with a temporal resolution of 3 as. This opens the door to new short-wavelength coherent control experiments with ultrahigh time resolution and chemical sensitivity.

At a glance


  1. Machine configuration used in the present study.
    Figure 1: Machine configuration used in the present study.

    Red waves indicate the first-harmonic radiation, and blue waves the second-harmonic radiation.

  2. Spectrometer set-up and image.
    Figure 2: Spectrometer set-up and image.

    a, Schematic set-up of the experimental station. The bichromatic light beam with fixed phase relation crosses the atomic jet of neon and ionizes the atoms. The VMI spectrometer measures the angular distribution of ejected electrons. The intensity is higher on the left or right, depending on the phase difference. b, Typical inverted VMI image, 6,000 shots. The strong, sharp ring is due to Ne 2p electrons, emitted by first- and second-harmonic light. A line profile across the centre of the image is shown (black line) at the bottom, demonstrating the left-right asymmetry (white arrows).

  3. Ionization scheme, β parameter variation and time resolution.
    Figure 3: Ionization scheme, β parameter variation and time resolution.

    a, Level diagram of the present experiment. A photoelectron may be ejected as a p-wave by a two-photon process, or as an (s+d)-wave by a one-photon process. b, Asymmetry parameter ALR as a function of Δɸ (red curve), and β1 (blue), β3 (magenta) and β2 (black) parameters as a function of Δɸ. Markers: experimental data; lines: sinusoidal fits for β1 and β3, linear fit for β2. Error bars determined using the procedure described in the Methods. c, Phase setting as a function of asymmetry parameter at the steepest part of the delay curve. Step size: 0.056 rad (900 zs). Steps were not sequential, so the measurement includes errors due to hysteresis in the system, if present. The residuals (difference between the straight line fit and the data) have a standard deviation of the phase corresponding to 3.1 as.


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Author information


  1. Elettra-Sincrotrone Trieste, 34149 Basovizza, Trieste, Italy

    • K. C. Prince,
    • E. Allaria,
    • C. Callegari,
    • R. Cucini,
    • G. De Ninno,
    • S. Di Mitri,
    • B. Diviacco,
    • E. Ferrari,
    • P. Finetti,
    • D. Gauthier,
    • L. Giannessi,
    • N. Mahne,
    • G. Penco,
    • O. Plekan,
    • L. Raimondi,
    • P. Rebernik,
    • E. Roussel,
    • C. Svetina,
    • M. Trovò &
    • M. Zangrando
  2. Molecular Model Discovery Laboratory, Department of Chemistry and Biotechnology, Swinburne University of Technology, Melbourne 3122, Australia

    • K. C. Prince
  3. Istituto Officina dei Materiali, Consiglio Nazionale delle Ricerche, 34149 Basovizza, Italy

    • K. C. Prince &
    • M. Zangrando
  4. Laboratory of Quantum Optics, University of Nova Gorica, Nova, Gorica 5001, Slovenia

    • G. De Ninno
  5. ENEA C.R. Frascati, 00044 Frascati, Rome, Italy

    • L. Giannessi
  6. University of Trieste, Graduate School of Nanotechnology, 34127 Trieste, Italy

    • C. Svetina
  7. Dipartimento di Fisica, CNR-IFN, Politecnico di Milano, Piazza Leonardo da Vinci, 32, 20133 Milan, Italy

    • M. Negro,
    • P. Carpeggiani,
    • M. Reduzzi &
    • G. Sansone
  8. Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow 119991, Russia

    • A. N. Grum-Grzhimailo,
    • E. V. Gryzlova &
    • S. I. Strakhova
  9. Department of Physics and Astronomy, Drake University, Des Moines, Iowa 50311, USA

    • K. Bartschat,
    • N. Douguet &
    • J. Venzke
  10. Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan

    • D. Iablonskyi,
    • Y. Kumagai,
    • T. Takanashi &
    • K. Ueda
  11. Max Planck Institute for Nuclear Physics, Heidelberg 69117, Germany

    • A. Fischer
  12. ISM, Consiglio Nazionale delle Ricerche, 34149 Basovizza, Italy

    • M. Coreno
  13. Physikalisches Institut, Universität Freiburg, 79106 Freiburg, Germany

    • F. Stienkemeier
  14. Institut für Optik und Atomare Physik, TU Berlin, Berlin, Germany

    • Y. Ovcharenko
  15. European XFEL, Albert-Einstein-Ring 19, 22761 Hamburg, Germany

    • T. Mazza &
    • M. Meyer


The experiment was conceived by K.C.P., G.S., A.N.G.G. and K.U., and the method of operating FERMI to carry it out was devised by E.A. and L.G. The experiment was prepared and carried out by K.C.P., E.A., C.C., R.C., G.D.N., S.D.M., B.D., E.F., P.F., D.G., L.G., N.M., G.P., O.P., L.R., P.R., E.R., C.S., M.T., M.Z., G.S., P.C., D.I., Y.K., T.T., K.U., A.F., F.S., E.O., T.M., M.N., M.C. and M.M. Theoretical calculations (of machine properties or neon spectra) were performed by E.A., L.G., A.N.G.G., E.V.G., S.I.S., K.B., N.D. and J.V. Detailed data analysis was performed by M.R., P.C. and D.I. The manuscript was drafted by K.C.P. and completed in consultation with all authors.

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