Femtosecond imaging of spatial deformation of surface plasmon polariton wave packet during resonant interaction with nanocavity.

The spatiotemporal dynamics of a surface plasmon polariton (SPP) wave packet (WP) that interacts with a plasmonic nanocavity on a metal surface are investigated via femtosecond time-resolved two-photon fluorescence microscopy and numerical calculations. The nanocavity, which consists of a metal-insulator-metal (MIM) laminar structure (longitudinal length: ∼100 nm), behaves as a subwavelength meta-atom possessing discretized eigenenergies. When a chirp-induced femto-second SPP WP is incident on the nanocavity, only the spectral component matching a particular eigenenergy is transmitted to continue propagation on the metal surface.

Spectral and temporal modulations of femtosecond SPP wave packets induced by resonant transmission/reflection interactions with metal-insulator-metal nanocavities.

To study the dynamical optical interactions of nano-scaled metal-insulator-metal (MIM) structures in temporal-frequency domain, femtosecond surface plasmon polariton (SPP) wave packets propagate over a surface with a MIM structure. The resonance nature of the SPP-cavity interaction is reflected as strong modulations in the spectra of transmitted and reflected SPP wavepackets, which show peaks and valleys, respectively, corresponding to the MIM cavity's eigenmode. These features indicate that the MIM structure acts as a Fabry-Pérot etalon-type spectrum filter.