We studied experimentally and theoretically the structural transition of diamond under an irradiation with an intense femtosecond extreme ultraviolet laser (XUV) pulse of 24–275 eV photon energy provided by free-electron lasers. Experimental results obtained showed that the irradiated diamond undergoes a solid-to-solid phase transition to graphite, and not to an amorphous state. Our theoretical findings suggest that the nature of this transition is nonthermal, stimulated by a change of the interatomic potential triggered by the excitation of valence electrons. Ultrashort laser pulse duration enables to identify the subsequent steps of this process: electron excitation, band gap collapse, and the following atomic motion. A good agreement between the experimentally measured and theoretically calculated damage thresholds for the XUV range supports our conclusions.
Local defects in diamond caused by focused XUV FEL pulse depicted by Nomarski DIC (differential interference contrast) microscopy.
1 Université de Bordeaux, CEA, CNRS, CELIA, UMR 5107, F-33400 Talence, France
2 European XFEL GmbH, Albert-Einstein-Ring 19, D-22761 Hamburg, Germany
3 Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany
4 Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, CZ-182 21 Prague 8, Czech Republic
5 HASYLAB/DESY, Notkestrasse 85, D-22607 Hamburg, Germany
6 Institut für Theoretische Physik, Goethe-Universität Frankfurt am Main, Max-von-Laue-Strasse 1, D-60438 Frankfurt, Germany
7 Institute of Physics Polish Academy of Sciences, Al. Lotników 32/46, PL-02-668 Warsaw, Poland
8 SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
9 Dutch Institute for Fundamental Energy Research, P.O. Box 1207, NL-3430 BE Nieuwegein, The Netherlands
10 RIKEN/SPring-8 Kouto 1-1-1, Sayo, Hyogo 679-5148, Japan
11 Institute of Materials Research, Slovak Academy of Sciences, SK-04001 Kosice, Slovak Republic
12 Institute of Physics, P. J. Šafárik University, Park Angelinum, SK-04154 Kosice, Slovak Republic
13 Faculty of Nuclear Science and Physical Engineering, Czech Technical University, CR-11519 Prague 1, Czech Republic
14 Institute of Nuclear Physics, Polish Academy of Sciences, Radzikowskiego 152, PL-31-342 Krakow, Poland
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