Femtosecond electronic response of atoms to ultra-intense X-rays


An era of exploring the interactions of high-intensity, hard X-rays with matter has begun with the start-up of a hard-X-ray free-electron laser, the Linac Coherent Light Source (LCLS). Understanding how electrons in matter respond to ultra-intense X-ray radiation is essential for all applications. Here we reveal the nature of the electronic response in a free atom to unprecedented high-intensity, short-wavelength, high-fluence radiation (respectively 1018 W cm−2, 1.5–0.6 nm, 105 X-ray photons per Å2). At this fluence, the neon target inevitably changes during the course of a single femtosecond-duration X-ray pulse—by sequentially ejecting electrons—to produce fully-stripped neon through absorption of six photons. Rapid photoejection of inner-shell electrons produces ‘hollow’ atoms and an intensity-induced X-ray transparency. Such transparency, due to the presence of inner-shell vacancies, can be induced in all atomic, molecular and condensed matter systems at high intensity. Quantitative comparison with theory allows us to extract LCLS fluence and pulse duration. Our successful modelling of X-ray/atom interactions using a straightforward rate equation approach augurs favourably for extension to complex systems.

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Figure 1: Diagram of the multiphoton absorption mechanisms in neon induced by ultra-intense X-ray pulses.
Figure 2: Neon charge-state yields for X-ray energies below, above and far above the 1 s -shell binding energy, 870 eV.
Figure 3: Intensity-induced X-ray transparency.
Figure 4: Electron spectra for inner-shell and valence photoelectrons and Auger electrons created by X-ray pulses at a photon energy of 1,050 eV.
Figure 5: The ratio of double- to single-core-hole formation as a function of X-ray pulse energy.


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We thank P. Emma, Z. Huang, R. Iverson, F. J. Decker, J. Frisch, and J. Turner for discussions that allowed us to realize, and subsequently utilize, the flexibility of the LCLS to maximum benefit. We are indebted to the operations staff for the performance of the LCLS in the many modes and energies that we requested throughout the course of this experiment. We thank the software engineers for producing advanced control, data acquisition and analysis capabilities during the experiment. This work was supported by the Chemical Sciences, Geosciences, and Biosciences Division of the Office of Basic Energy Sciences, Office of Science, US Department of Energy (DE-AC02-06CH11357, DE-FG02-04ER15614, DE-FG02-92ER14299). N.R. was supported by the US Department of Energy by Lawrence Livermore National Laboratory (DE-AC52-07NA27344). M.H. thanks the Alexander von Humboldt Foundation for a Feodor Lynen fellowship. P.H.B., J.P.C., S.G., J.M.G. and D.A.R. were supported through the PULSE Institute, which is jointly funded by the Department of Energy, Basic Energy Sciences, Chemical Sciences, Geosciences and Biosciences Division and Division of Materials Science and Engineering. Portions of this research were carried out at the LCLS at the SLAC National Accelerator Laboratory. LCLS is funded by the US Department of Energy’s Office of Basic Energy Sciences.

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L.Y., R.S., S.H.S., E.P.K. and B.K. conceived the experimental plan, acquired and analysed the data, and wrote the paper. R.S. and N.R. performed the theoretical calculations. J.D.B. and C.B. designed, commissioned and operated the AMO instrument. M.M. assisted during the experiment with upstream X-ray diagnostics. Y.L., A.M.M., S.T.P., L.F.D., G.D., C.A.R., N.B., L.F., M.H., P.H.B., J.P.C., S.G., J.M.G. and D.A.R. contributed to the experiment. All authors contributed to the work presented here and to the final paper.

Correspondence to L. Young.

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Young, L., Kanter, E., Krässig, B. et al. Femtosecond electronic response of atoms to ultra-intense X-rays. Nature 466, 56–61 (2010). https://doi.org/10.1038/nature09177

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