Optical Forces Between Coupled Plasmonic Nano-particles near Metal Surfaces and Negative Index Material Waveguides

TL;DR

This paper investigates how light-induced forces between coupled plasmonic nanoparticles are affected by different slab geometries, including metal and negative index materials, revealing complex interactions and the importance of loss reduction.

Contribution

It introduces a non-perturbative Green function approach to analyze optical forces near complex slab geometries, including NIMs, highlighting the effects of slow-light modes and loss reduction.

Findings

Optical forces are significantly influenced by surface plasmon polariton and slow-light waveguide modes.

Optical quenching reduces the spatial range of inter-particle forces.

Reducing NIM loss enhances the forces through better radiation propagation.

Abstract

We present a study of light-induced forces between two coupled plasmonic nano-particles above various slab geometries including a metallic half-space and a 280-nm thick negative index material (NIM) slab waveguide. We investigate optical forces by non-perturbatively calculating the scattered electric field via a Green function technique which includes the particle interactions to all orders. For excitation frequencies near the surface plasmon polariton and slow-light waveguide modes of the metal and NIM, respectively, we find rich light-induced forces and significant dynamical back-action effects. Optical quenching is found to be important in both metal and NIM planar geometries, which reduces the spatial range of the achievable inter-particle forces. However, reducing the loss in the NIM allows radiation to propagate through the slow-light modes more efficiently, thus causing the light-induced forces to be more pronounced between the two particles. To highlight the underlying mechanisms by which the particles couple, we connect our Green function calculations to various familiar quantities in quantum optics.