Detecting nonlinear acoustic waves in liquids with nonlinear dipole optical antennae

TL;DR

This paper proposes using nonlinear optical nanoantennas made of silver nanorods to detect high-frequency acoustic waves in water through Brillouin light scattering, enabling high-resolution ultrasound imaging at the nanoscale.

Contribution

It introduces a novel method of detecting nonlinear acoustic waves using high-order plasmon modes in silver nanorods as optical dipole antennas.

Findings

Demonstrated theoretical feasibility of detecting acoustic waves with nanorods.

Showed enhancement of third-harmonic generation in high-order plasmon modes.

Proposed a new nanoscale ultrasound detection technique.

Abstract

Ultrasound is an important imaging modality for biological systems. High-frequency ultrasound can also (e.g., via acoustical nonlinearities) be used to provide deeply penetrating and high-resolution imaging of vascular structure via catheterisation. The latter is an important diagnostic in vascular health. Typically, ultrasound requires sources and transducers that are greater than, or of order the same size as the wavelength of the acoustic wave. Here we design and theoretically demonstrate that single silver nanorods, acting as optical nonlinear dipole antennae, can be used to detect ultrasound via Brillouin light scattering from linear and nonlinear acoustic waves propagating in bulk water. The nanorods are tuned to operate on high-order plasmon modes in contrast to the usual approach of using fundamental plasmon resonances. The high-order operation also gives rise to enhanced optical third-harmonic generation, which provides an important method for exciting the higher-order Fabry-Perot modes of the dipole antenna.