Soft-x-ray harmonic comb from relativistic electron spikes

A. S. Pirozhkov, M. Kando, T. Zh Esirkepov, P. Gallegos, H. Ahmed, E. N. Ragozin, A. Ya Faenov, T. A. Pikuz, T. Kawachi, A. Sagisaka, J. K. Koga, M. Coury, J. Green, P. Foster, C. Brenner, B. Dromey, D. R. Symes, M. Mori, K. Kawase, T. KameshimaY. Fukuda, L. Chen, I. Daito, K. Ogura, Y. Hayashi, H. Kotaki, H. Kiriyama, H. Okada, N. Nishimori, T. Imazono, K. Kondo, T. Kimura, T. Tajima, H. Daido, P. Rajeev, P. McKenna, M. Borghesi, D. Neely, Y. Kato, S. V. Bulanov

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62 Citations (Scopus)


We demonstrate a new high-order harmonic generation mechanism reaching the "water window" spectral region in experiments with multiterawatt femtosecond lasers irradiating gas jets. A few hundred harmonic orders are resolved, giving mu J/sr pulses. Harmonics are collectively emitted by an oscillating electron spike formed at the joint of the boundaries of a cavity and bow wave created by a relativistically self-focusing laser in underdense plasma. The spike sharpness and stability are explained by catastrophe theory. The mechanism is corroborated by particle-in-cell simulations.

Original languageEnglish
Article number135004
Pages (from-to)-
Number of pages5
JournalPhysical Review Letters
Issue number13
Publication statusPublished - 30 Mar 2012


  • x-ray harmonic comb
  • harmonic comb
  • relativistic electron spikes
  • electron spikes

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