Measuring the temporal structure of few-femtosecond free-electron laser X-ray pulses directly in the time domain

W. Helml, A. R. Maier, W. Schweinberger, I. Grguraš, P. Radcliffe, G. Doumy, C. Roedig, J. Gagnon, M. Messerschmidt, S. Schorb, C. Bostedt, F. Grüner, L. F. Dimauro, D. Cubaynes, J. D. Bozek, Th Tschentscher, J. T. Costello, M. Meyer, R. Coffee, S. DüstererA. L. Cavalieri, R. Kienberger

Research output: Contribution to journalArticlepeer-review

94 Scopus citations


Short-wavelength free-electron lasers are now well established as essential and unrivalled sources of ultrabright coherent X-ray radiation. One of the key characteristics of these intense X-ray pulses is their expected few-femtosecond duration. No measurement has succeeded so far in directly determining the temporal structure or even the duration of these ultrashort pulses in the few-femtosecond range. Here, by deploying the so-called streaking spectroscopy technique at the Linac Coherent Light Source, we demonstrate a non-invasive scheme for temporal characterization of X-ray pulses with sub-femtosecond resolution. This method is independent of photon energy, decoupled from machine parameters, and provides an upper bound on the X-ray pulse duration. We measured the duration of the shortest X-ray pulses currently available to be on average no longer than 4.4...fs. Analysing the pulse substructure indicates a small percentage of the free-electron laser pulses consisting of individual high-intensity spikes to be on the order of hundreds of attoseconds.

Original languageEnglish (US)
Pages (from-to)950-957
Number of pages8
JournalNature Photonics
Issue number12
StatePublished - Nov 27 2014
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Atomic and Molecular Physics, and Optics


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