Spatiotemporal control of surface plasmon polariton wave packets with nanocavities

TL;DR

This paper demonstrates how nanocavities can control the spatiotemporal dynamics of surface plasmon polariton wave packets, enabling tunable group velocities including superluminal and negative speeds.

Contribution

It introduces a method to modulate surface plasmon polariton wave packets using nanocavities with tunable eigenmodes, achieving controllable group velocity effects.

Findings

Spectral clipping of SPP wave packets by nanocavities.

Adjustable spatial shifts corresponding to different group velocities.

Demonstration of superluminal, subluminal, and negative group velocities.

Abstract

Modulation of the optical index by means of atomic and material resonances provides a basis for controlling light propagation in natural and artificially fabricated materials. In addition, recent advances in the tuning of spatiotemporal couplings of ultrashort laser pulses have enabled almost arbitrary control over the group velocity of light. Here, using femtosecond time-resolved microscopy and numerical calculations, we investigate the spatiotemporal dynamics of a surface plasmon polariton wave packet (SPP WP) that interacts with a plasmonic nanocavity. The nanocavity consists of metal-insulator-metal multilayer films that function as subwavelength meta-atom possessing tunable discretized eigenmodes. When a chirp-induced femtosecond SPP WP is incident on a nanocavity, only the spectral component matching the resonance energy is transmitted. This spectral clipping effect is accompanied by a spatial shift of the WP. The shift can be adjusted in either the positive or negative direction by controlling the resonance energy or the chirp. If this spatial shift is regarded as a modulation of the apparent group velocity in the nanocavity, the range of modulation includes superluminal, subluminal, and negative group velocities.