The Large Near-Field Enhancement due to Strong Coupling Between the LSP on the Metal Coupled Nanodisks and on the Gold Film for Short Attosecond Pulse Generation

Abstract

Within a mid-IR few-cycle laser, the generation of MHz isolated attosecond pulses via nanoplasmonic field enhancement in a structure that consisted of a metal coupled nanoparticle-disk, an insulator spacer, and a thin metal film is theoretically investigated. The interaction between the localized surface plasmons caused by the coupled nanodisks and the metal layer results in increased electric field. The resonance wavelengths of these two types of surface plasmons supported by the nanostructure are tailored by changing the coupled nanoparticle-disk size and the material type. Numerical calculations are used to optimize nanostructure and attain plasmonic field enhancement factors up to 86. The HHG process is studied by the time–frequency analysis. Our studies show that only short trajectories contribute to HHG and also, the chirp of these harmonics is very low. As a result, an isolated 40 as pulse without phase compensation is obtained directly by superposing the chirp-free high-order harmonics.