Optical Forces in Coupled Chiral Particles

TL;DR

This paper explores the complex optical forces between coupled chiral particles, revealing how their interactions depend on handedness, resonance modes, and coupling, with implications for optical manipulation and chiral light-matter interactions.

Contribution

It introduces a combined numerical and analytical approach to study optical forces in coupled chiral particles, highlighting the role of resonance modes and handedness in force behavior.

Findings

Attractive forces are stronger between particles of opposite handedness.

Resonance modes significantly enhance interaction forces.

Electric and magnetic dipole forces can have same or opposite signs depending on handedness.

Abstract

Structural chirality can induce counter-intuitive optical forces due to inherent symmetry properties. While optical forces on a single chiral particle in the Rayleigh regime have been well studied, optical forces in coupled chiral particles remain less explored. By using full-wave numerical simulations and analytical methods of source representation and coupled mode theory, we investigated the optical forces induced by a plane wave on two chiral particles coupling with each other via the evanescent near fields. We found that the induced electric and magnetic dipoles of the chiral particles have complicated couplings that give rise to dark and bright modes. The interaction force between the particles can be either attractive or repulsive, and its magnitude can be significantly enhanced by the resonance modes. The attractive force is much stronger if two particles are of opposite handedness compared with the case of same handedness. The electric dipole force and the magnetic dipole force have the same sign for two particles with the same handedness, while they are of different signs for two particles with opposite handedness. The results can lead to a better understanding of chirality-induced optical forces with potential applications in optical manipulations and chiral light-matter interactions.