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Energy Bunching from Subcycle Ionization Injection in Laser Wakefield Acceleration

A. Angella*, E. Löfquist, C. Gustafsson, V. Poulain, F. D’Souza, C. Guo, A. Persson, P. Eng-Johnsson, C.-G. Wahlström et al.

O. Lundh†

  • Department of Physics, Lund University, P.O. Box 118, SE-22100 Lund, Sweden

  • *Contact author: andrea.angella@fysik.lu.se
  • †Contact author: olle.lundh@fysik.lu.se

Phys. Rev. Lett. 136, 065001 – Published 10 February, 2026

DOI: https://doi.org/10.1103/kwlg-yjl9

Abstract

We report the first experimental observation of carrier-envelope phase-driven energy bunching in laser wakefield acceleration. Using a few-cycle (∼9  fs), multiterawatt laser pulse and ionization injection in a helium-nitrogen gas mixture, we observe electron spectra composed of multiple quasimonoenergetic peaks with regular narrow energy spacing. This comb structure arises from intermittent trapping from successive half-cycles of the laser field enabled by the evolving carrier-envelope phase during propagation in the plasma. These findings establish subcycle ionization injection as a potential route to attosecond control in plasma acceleration, enabling trapping and beam structuring synchronized to the optical waveform on subfemtosecond timescales.

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