Ultrafast Acousto-Plasmonics in Gold Nanoparticles Superlattice

TL;DR

This study explores ultrafast generation and detection of coherent acoustic phonons in gold nanoparticle superlattices using femtosecond pump-probe techniques, revealing insights into phonon dynamics and elastic properties at the nanoscale.

Contribution

It provides new experimental insights into phonon generation mechanisms and elastic responses in plasmonic gold nanoparticle superlattices.

Findings

Estimated collective elastic response and sound velocity of NPS.

Observed phonon pulse extension of about 45 nm.

Identified ultrafast heating and volume plasmon excitation as phonon generation mechanisms.

Abstract

We report the investigation of the generation and detection of GHz coherent acoustic phonons in plasmonic gold nanoparticles superlattices (NPS). The experiments have been performed from an optical femtosecond pump-probe scheme across the optical plasmon resonance of the superlattice. Our experiments allow to estimate the collective elastic response (sound velocity) of the NPS as well as an estimate of the nano-contact elastic stiffness. It appears that the light-induced coherent acoustic phonon pulse has a typical in-depth spatial extension of about 45 nm which is roughly 4 times the optical skin depth in gold. The modeling of the transient optical reflectivity indicates that the mechanism of phonon generation is achieved through ultrafast heating of the NPS assisted by light excitation of the volume plasmon. These results demonstrate how it is possible to map the photon-electron-phonon interaction in subwavelength nanostructures.