Visualization and Control of Quasi-Monoenergetic Proton Shock Waves in a Single Nanoplasma

This work demonstrates direct visualization and deterministic control of quasi-monoenergetic proton shock waves from isolated gold nanoparticles under intense femtosecond laser irradiation. Using single-shot nano-velocity map imaging, we observe a continuous circular shock wave profile in momentum space, reflecting the formation of a symmetric proton shell in space. Two-stage simulations, combining a modified particle-in-cell method with a dissipative Gross–Pitaevskii equation, reveal their formation and expansion on femtosecond–picosecond timescales. Crucially, the proton shock wave energy can be modulated by tuning the laser intensity. These findings provide fundamental insights into strong-field nanoplasma dynamics and establish a practical scheme for compact, laser-driven ion sources with on-demand energy tunability.