Strong-field photoelectron (PE) emission of plasmonic nanoparticles (NPs)*

We measured [1] and numerically simulated [2] velocity-map-imaging (VMI) maps resulting from the strong-field PE emission of metal NPs by intense infrared laser pulses. Our semi-classical model consists of two distinct steps: (i) PE release by tunneling induced by an intense IR laser pulse and (ii) classical PE propagation to the detector within a trajectory sampling approach [3], distinguishing the effects of PE correlation, PE - residual-charge interactions, PE rescattering and recombination, and transient laser-induced plasmonic fields. By comparing our experimental and numerical results for 5, 30, and 70 nm diameter gold nanospheres and peak laser-pulse intensities of 8×10¹² and 1.2×10¹³ W/cm², we showed how VMI maps are distinctly shaped by PE Coulomb repulsion, residual-charge accumulations, and plasmonic near fields. Compared to gaseous atomic targets [4], we find much larger PE cutoff energies. These exceed the incident laser-pulse ponderomotive energy by two orders of magnitude, for both directly emitted and rescattered PEs.