Optical forces in nanorod metamaterial

TL;DR

This paper explores how a 3D nanorod metamaterial can enhance optical manipulation of nano-objects by supporting near-field interactions and controlling optical forces, with minimal impact from topological dispersion transitions.

Contribution

It introduces a nanorod metamaterial platform for optical manipulation that maintains force distribution across topological transitions, supported by a semi-analytical model and numerical simulations.

Findings

Metamaterial supports near-field interactions for optical trapping.

Topological transition does not significantly alter force distribution.

Semi-analytical model agrees with full-wave simulations.

Abstract

Optomechanical manipulation of micro and nano-scale objects with laser beams finds use in a large span of multidisciplinary applications. Auxiliary nanostructuring could substantially improve performances of classical optical tweezers by means of spatial localization of objects and intensity required for trapping. Here we investigate a three-dimensional nanorod metamaterial platform, serving as an auxiliary tool for the optical manipulation, able to support and control near-field interactions and generate both steep and flat optical potential profiles. It was shown that the 'topological transition' from the elliptic to hyperbolic dispersion regime of the metamaterial, usually having a significant impact on various light-matter interaction processes, does not strongly affect the distribution of optical forces in the metamaterial. This effect is explained by the predominant near-fields contributions of the nanostructure to optomechanical interactions. Semi-analytical model, approximating the finite size nanoparticle by a point dipole and neglecting the mutual re-scattering between the particle and nanorod array, was found to be in a good agreement with full-wave numerical simulation. In-plane (perpendicular to the rods) trapping regime, saddle equilibrium points and optical puling forces (directed to the excitation light source along the rods), acting on a particle situated inside or at the nearby the metamaterial, were found. The auxiliary metamaterials, employed for optical manipulation, provide additional degrees of freedom in flexible nano-mechanical control and could be employed in various cross-disciplinary applications.