Transverse optical binding for a dual dipolar dielectric nanoparticle dimer

Abstract

The physical origins of the transverse optical binding force and torque beyond the Rayleigh approximation have not been clearly expressed to date. Here, we present analytical expressions of the force and torque for a dual dipolar dielectric dimer illuminated by a plane wave propagating perpendicularly to the dimer axis. Using this analytical model, we explore the roles of the hybridized electric dipolar, magnetic dipolar, and electric-magnetic dipolar coupling interactions in the total force and torque on the particles. We find significant departures from the predictions of the Rayleigh approximation, particularly for high-refractive-index particles, where the force is governed by the magnetic interaction. This results in an enhancement of the dimer stability by one to four orders of magnitude compared to the predictions of the Rayleigh approximation. For the case of torque, this is dominated by the coupling interaction and increases by an order of magnitude. Our results will help to guide future experimental work in optical binding of high-refractive-index dielectric particles.

Asymmetric longitudinal optical binding force between two identical dielectric particles with electric and magnetic dipolar responses

“…Consequently, FRay grossly underestimates the LOBF and even departs from Fe where the magnetic and electric-magnetic coupling effects are considered. This is similar to the TOBF for dielectric particles [30]. On the other hand, we focus on the stable and unstable equilibrium positions of FRay and LOBF (also termed the stable and unstable equilibrium separations of the two particles).…”

“…In the framework of the optical force on a single dielectric particle [28] and electromagnetic wave mutual scattering [29] (or see Appendices in Ref. [30]), the LOBF is analytically decomposed into the electric dipolar, magnetic dipolar, and electric-magnetic dipolar coupling components. In detail, the electric dipolar component of the LOBF on particle j (j=A or B) is expressed as…”

“…1 (a)], ∂/∂R denotes the partial derivative with respect to R. k=2π/λ is the wavenumber in the medium, λ and λ0 are respectively the incident wavelength in the medium and vacuum with relation λ=λ0/ns. μ=exp(ikR)(k 2 R 2 +ikR-1)/(4πR 3 ) and η=exp(ikR)(ik 2 R 2 -kR)/(4πR 3 ) are respectively the eigenvalues of the electric and magnetic dyadic Green's functions of a point dipole [30]. Note that the terms on the right side of Eq.…”

“…In detail, the hybridization refers to the fact that the ED (MD) in one particle is affected by the radiated electric (magnetic) fields of the ED and MD in the neighboring particle [34]. On the other hand, the coupling comes from the interaction between the ED and MD in one particle [30]. For the ED (MD) moment in Eq.…”

Optical trapping with structured light: a review

“…The double-well potential can be used to study collective particle dynamics, e.g., optical binding 21 and forces between levitated particles. 210 Arita et al 211 demonstrated trapping and rotation of two microparticles in vacuum using an SLM-based approach, allowing individual control over the rotation direction and rate to each trap and the interparticle separation. By trapping and rotating two vaterite birefringent microparticles with circularly polarized light, they observed macroscopic Raman-like modulation of the incident light field at the sum and difference frequencies with respect to the individual rotation rates.…”