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Abstract

The generation of extremely bright coherent X-ray pulses in the femtosecond and attosecond regime is currently one of the most exciting frontiers of physics–allowing, for the first time, measurements with unprecedented temporal resolution1,2,3,4,5,6. Harmonics from laser–solid target interactions have been identified as a means of achieving fields as high as the Schwinger limit2,7 (E=1.3×1016 V m−1) and as a highly promising route to high-efficiency attosecond (10−18 s) pulses8 owing to their intrinsically phase-locked nature. The key steps to attain these goals are achieving high conversion efficiencies and a slow decay of harmonic efficiency to high orders by driving harmonic production to the relativistic limit1. Here we present the first experimental demonstration of high harmonic generation in the relativistic limit, obtained on the Vulcan Petawatt laser9. High conversion efficiencies (η>10−6 per harmonic) and bright emission (>1022 photons s−1 mm−2 mrad−2 (0.1% bandwidth)) are observed at wavelengths <4 nm (the `water-window' region of particular interest for bio-microscopy).

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Acknowledgements

We would like to acknowledge the support of the European Social Fund (B.D.). M.Z. holds a Royal Society-Wolfson Research Merit Award.

Author information

Affiliations

  1. Department of Physics and Astronomy, Queen's University Belfast BT7 1NN, UK

    • B. Dromey
    •  & M. Zepf
  2. Blackett Laboratory, Imperial College, London SW7 2BZ, UK

    • A. Gopal
    • , K. Lancaster
    • , M. S. Wei
    •  & K. Krushelnick
  3. Department of Electronics, Technological Educational Institute of Crete, 73133 Chania, Greece

    • M. Tatarakis
  4. Technical University of Crete, Institute of Matter Struct. & Laser Phys. Chania, 73132 Chania, Greece

    • N. Vakakis
    •  & S. Moustaizis
  5. ILE University of Osaka, 565-0871 Osaka, Japan

    • R. Kodama
    •  & M. Tampo
  6. Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623-1299, USA

    • C. Stoeckl
  7. Central Laser Facility, CCLRC Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UK

    • R. Clarke
    • , H. Habara
    • , D. Neely
    • , S. Karsch
    •  & P. Norreys

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The authors declare no competing financial interests.

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Correspondence to M. Zepf.

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https://doi.org/10.1038/nphys338

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