Plasma dynamics in transient electrostatic shocks driven by relativistic few-cycle laser pulses

The rapid advancement of laser compression techniques has brought increasing attention to few-cycle laser-plasma interactions. Through comprehensive particle-in-cell simulations, we demonstrate that compressing laser pulses to sub-10-femtosecond durations significantly enhances transient electrostatic shocks. Crucially, the plasma dynamics are strongly modulated by the laser carrier-envelope phase ( Φ CEP ). Our results reveal a pronounced cosinelike dependence of the proton cutoff energy on Φ CEP , with certain values of Φ CEP yielding superior performance due to enhanced electron displacement and stronger charge-separation fields. Phase-space analysis uncovers expanding “source”-like electron orbits, whose gyration radii correlate with Φ CEP -dependent energy transfer. We further develop an analytical model connecting the electrostatic shock strength, inferred from the proton energy, to the laser-plasma interaction parameters. This model is validated through extensive parameter scans over target density, thickness, laser intensity, and Φ CEP . Our findings establish a predictive framework for Φ CEP -controlled plasma dynamics in short-pulse laser interactions, providing insight into mechanisms relevant to laboratory high-energy proton sources and origin of energetic cosmic rays in astrophysical environments.