An intense laser pulse in a plasma can accelerate electrons1,2,3,4 to GeV energies in centimetres5,6,7. Transverse betatron motion8,9 in the plasma wake results in X-ray photons with an energy that depends on the electron energy, oscillation amplitude and frequency of the betatron motion10,11,12. Betatron X-rays from laser-accelerator electrons have hitherto been limited to spectra peaking between 1 and 10 keV (ref. 13). Here we show that the betatron amplitude is resonantly enhanced when electrons interact with the rear of the laser pulse14,15. At high electron energy, resonance occurs when the laser frequency is a harmonic of the betatron frequency, leading to a significant increase in the photon energy. 108 gamma-ray photons, with spectra peaking between 20 and 150 keV, and a peak brilliance >1023 photons s−1 mrad−2 mm−2 per 0.1% bandwidth, are measured for 700 MeV beams, with 107 photons emitted between 1 and 7 MeV. Femtosecond duration gamma-rays may find uses in imaging, isotope production, probing dense matter, homeland security and nuclear physics16.

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We acknowledge the support of the UK EPSRC, STFC, the Laserlab-Europe consortium and the Extreme Light Infrastructure (ELI) project. Over the past decade many current and previous members of the ALPHA-X consortium have made contributions to the project, for which we extend thanks. We also thank D. Clark and T. McCanny for their technical support, without which the project would not have been possible. The authors would like to thank the OSIRIS consortium (UCLA/IST) for the use of OSIRIS. The work of NRCL was partially supported by FCT Portugal through the grant SFRH/BD/37838/2007

Author information


  1. University of Strathclyde, Department of Physics, Scottish Universities Physics Alliance, John Anderson Building, 107 Rottenrow, Glasgow, G4 0NG, UK

    • Silvia Cipiccia
    • , Mohammad R. Islam
    • , Bernhard Ersfeld
    • , Richard P. Shanks
    • , Enrico Brunetti
    • , Gregory Vieux
    • , Xue Yang
    • , Riju C. Issac
    • , Samuel M. Wiggins
    • , Gregor H. Welsh
    • , Maria-Pia Anania
    •  & Dino A. Jaroszynski
  2. University of Glasgow, Department of Physics and Astronomy, Scottish Universities Physics Alliance, Glasgow, G12 8QQ, UK

    • Dzmitry Maneuski
    • , Rachel Montgomery
    • , Gary Smith
    • , Matthias Hoek
    • , David J. Hamilton
    •  & Val O. Shea
  3. GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Avenida Rovisco Pais 1049-001, Lisbon, Portugal

    • Nuno R. C. Lemos
    •  & João M. Dias
  4. Central Laser Facility, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, OX11 0QX, UK

    • Dan Symes
    •  & Pattathil P. Rajeev


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The experiment was conceived by D.A.J. The experiments and equipment calibration were undertaken by S.C., R.P.S, E.B., G.V., X.Y., R.C.I., S.M.W., G.H.W., M-P.A., D.M., R.M., G.S., M.H., D.J.H., N.R.C.L., V.O.S., J.M.D. and D.A.J. Theoretical analysis, interpretation and simulations were carried out by M.R.I., B.E., S.C. and D.A.J. The laser and target area operators were D.S. and P.P.R. The manuscript was prepared in the main by D.A.J., S.C., B.E. and M.R.I., with the reviewing and comment input of R.C.I., S.M.W., G.H.W., N.R.C.L. and J.M.D.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Dino A. Jaroszynski.

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