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Laser plasma acceleration with a negatively chirped pulse: all-optical control over dark current in the blowout regime
New Journal of Physics (2012)
  • Serguei Y. Kalmykov
  • Arnaud Beck
  • Xavier Davoine
  • Erik Lefebvre
  • Bradley A. Shadwick

Recent experiments with 100 terawatt-class, sub-50 femtosecond laser pulses show that electrons self-injected into a laser-driven electron density bubble can be accelerated above 0.5 gigaelectronvolt energy in a sub-centimetre length rarefied plasma. To reach this energy range, electrons must ultimately outrun the bubble and exit the accelerating phase; this, however, does not ensure high beam quality. Wake excitation increases the laser pulse bandwidth by red-shifting its head, keeping the tail unshifted. Anomalous group velocity dispersion of radiation in plasma slows down the red-shifted head, compressing the pulse into a few-cycle-long piston of relativistic intensity. Pulse transformation into a piston causes continuous expansion of the bubble, trapping copious numbers of unwanted electrons (dark current) and producing a poorly collimated, polychromatic energy tail, completely dominating the electron spectrum at the dephasing limit. The process of piston formation can be mitigated by using a broad-bandwidth (corresponding to a few-cycle transform-limited duration), negatively chirped pulse. Initial blue-shift of the pulse leading edge compensates for the nonlinear frequency red-shift and delays the piston formation, thus significantly suppressing the dark current, making the leading quasi-monoenergetic bunch the dominant feature of the electron spectrum near dephasing. This method of dark current control may be feasible for future experiments with ultrahigh-bandwidth, multi-joule laser pulses.

  • Laser wakefield acceleration,
  • blowout regime,
  • electron self-injection,
  • optical shock,
  • particle-in-cell simulations
Publication Date
Spring March 15, 2012
Citation Information
Serguei Y. Kalmykov, Arnaud Beck, Xavier Davoine, Erik Lefebvre, and Bradley A. Shadwick. "Laser plasma acceleration with a negatively chirped pulse: all-optical control over dark current in the blowout regime" New Journal of Physics 14 (2012) 033025. Available at: