Enhanced cutoff energies for direct and rescattered strong-field photoelectron emission of plasmonic nanoparticles*

We here demonstrate the generation of photoelectrons (PEs) by exposing plasmonic nanostructures to intense laser pulses in the infrared (IR) spectral regime and analyze the susceptibility of PE spectra to competing for elementary interactions for direct and rescattered photoemission pathways. Specifically, we measured and numerically simulated emitted PE momentum distributions from prototypical spherical gold nanoparticles (NPs) with diameters between 5 and 70 nm generated by short laser pulses with peak intensities of 8×10¹² and 1.2 ×10¹³ W/cm² [1,2], demonstrating the shaping of PE spectra by the Coulomb repulsion between PEs, accumulating residual charges on the NP, and induced plasmonic electric fields[2]. We scrutinized the controllability of the direct and rescattered PE yield and cutoff energy by tuning the laser intensity and NP size. Compared to well-understood PE cutoff energies for strong-field photoemission from gaseous atomic targets (10 × the ponderomotive energy), our measured and simulated PE spectra reveal a dramatic cutoff-energy increase of two orders of magnitude with a significantly higher contribution from direct photoemission. Our findings indicate that direct PEs reach up to 93% of the rescattered electron cutoff energy, in contrast to 20% for gaseous atoms, suggesting a novel scheme for the development of compact tunable tabletop electron sources [3].