High order harmonics from relativistic electron spikes

Alexander S. Pirozhkov, Masaki Kando, Timur Zh Esirkepov, Pablo Gallegos, Hamad Ahmed, Eugene N. Ragozin, Anatoly Ya Faenov, Tatiana A. Pikuz, Tetsuya Kawachi, Akito Sagisaka, James K. Koga, Mireille Coury, James Green, Peta Foster, Ceri Brenner, Brendan Dromey, Dan R. Symes, Michiaki Mori, Keigo Kawase, Takashi KameshimaYuji Fukuda, Liming Chen, Izuru Daito, Koichi Ogura, Yukio Hayashi, Hideyuki Kotaki, Hiromitsu Kiriyama, Hajime Okada, Nobuyuki Nishimori, Takashi Imazono, Kiminori Kondo, Toyoaki Kimura, Toshiki Tajima, Hiroyuki Daido, Pattathil Rajeev, Paul McKenna, Marco Borghesi, David Neely, Yoshiaki Kato, Sergei V. Bulanov

Research output: Contribution to journalArticlepeer-review

25 Citations (Scopus)

Abstract

A new regime of relativistic high-order harmonic generation has been discovered (Pirozhkov 2012 Phys. Rev. Lett. 108 135004). Multi-terawatt relativistic-irradiance (>1018W cm-2) femtosecond (∼30-50 fs) lasers focused to underdense (few × 1019cm-3) plasma formed in gas jet targets produce comb-like spectra with hundreds of even and odd harmonic orders reaching the photon energy of 360 eV, including the 'water window' spectral range. Harmonics are generated either by linearly or circularly polarized pulses from the J-KAREN (KPSI, JAEA) and Astra Gemini (CLF, RAL, UK) lasers. The photon number scalability has been demonstrated with a 120 TW laser, producing 40 μJ sr-1 per harmonic at 120 eV. The experimental results are explained using particle-in-cell simulations and catastrophe theory. A new mechanism of harmonic generation by sharp, structurally stable, oscillating electron spikes at the joint of the boundaries of the wake and bow waves excited by a laser pulse is introduced. In this paper, detailed descriptions of the experiments, simulations and model are provided and new features are shown, including data obtained with a two-channel spectrograph, harmonic generation by circularly polarized laser pulses and angular distribution.

Original languageEnglish
Article number093003
JournalNew Journal of Physics
Volume16
DOIs
Publication statusPublished - 2014

Keywords

  • gas jet target
  • high-order harmonics
  • relativistic electron spikes
  • relativistic laser plasma

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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