A laser pulse propagating in plasma excites collective oscillations of charged particles such as electrons as well as ions. By exploiting the collective oscillation of electrons, a.k.a. plasma wave, laser-driven electron acceleration in underdense plasma has made great achievements. Since ions are much heavier than electrons, the collective oscillation of ions, which we call ion wave, can be significant only with strong excitation, which happens when propagating ultra-intense laser pulses in near- or over-critical relativistically transparent plasma. Although there are some differences between the ion wave and its electronic counterpart, they share some intrinsic features. The successful methods used in electron acceleration inspire us to find new approaches for high-energy ion acceleration, which appear promising.

B. Liu, M. Shi, M. Zepf, B. Lei, and D. Seipt, Accelerating Ions by Crossing Two Ultraintense Lasers in a Near-Critical Relativistically Transparent Plasma, Phys. Rev. Lett. 129, 274801 (2022).

B. Liu, J. Meyer-ter-Vehn, and H. Ruhl, Self-trapping and acceleration of ions in laser-driven relativistically transparent plasma, Physics of Plasmas 25, 103117 (2018).

B. Liu, J. Meyer-ter-Vehn, K.-U. Bamberg, W. J. Ma, J. Liu, X. T. He, X. Q. Yan, and H. Ruhl, Ion wave breaking acceleration, Phys. Rev. Accel. Beams 19, 073401 (2016).