Exciting space-time surface plasmon polaritons by irradiating a nanoslit structure

TL;DR

This paper demonstrates, through simulations, that space-time wave packets can be effectively coupled to surface plasmon polaritons via a nanoslit, creating localized, propagation-invariant plasmonic waves with tunable velocities.

Contribution

It introduces a novel excitation method for surface-bound space-time wave packets using a nanoslit, enabling diffractionless, dispersionless plasmonic 'bullets' with tunable speeds.

Findings

Successful coupling of ST wave packets to ST-SPPs via nanoslit

Surface-bound ST-SPPs are localized and propagate without diffraction or dispersion

Tunable group velocity of plasmonic bullets achieved

Abstract

Space-time (ST) wave packets are propagation-invariant pulsed optical beams that travel freely in dielectrics at a tunable group velocity without diffraction or dispersion. Because ST wave packets maintain these characteristics even when only one transverse dimension is considered, they can realize surface-bound waves (e.g., surface plasmon polaritons at a metal-dielectric interface, which we call ST-SPPs) that have the same unique characteristics of their freely propagating counterparts. However, because the spatio-temporal spectral structure of ST-SPPs is key to their propagation invariance on the metal surface, their excitation methodology must be considered carefully. We show here using finite-difference time-domain (FDTD) simulations that an appropriately synthesized ST wave packet in free space can be couples to a ST-SPP via a single nano-scale slit inscribed in the metal surface. Our calculations confirm that this excitation methodology yields surface-bound ST-SPPs that are locarized in all dimensions (and can thus be considered as plasmonic 'bullets'), which travel rigidly at the metal-dielectric interface without diffraction or dispersion at a tunable group velocity.