Tailoring optical pulling forces with composite microspheres

TL;DR

This paper develops a theoretical framework to tailor optical pulling forces on composite microspheres using superpositions of plane waves, enabling new control strategies for tractor beams beyond traditional Bessel beam methods.

Contribution

It introduces a novel theoretical approach combining Mie theory and Wigner rotations to analyze and optimize optical pulling forces on composite particles with plasmonic inclusions.

Findings

Composite particles can generate polarization-dependent pulling forces.

Adding plasmonic inclusions enhances the optical pulling force capabilities.

The framework enables tailored optical forces for improved tractor beam applications.

Abstract

Optical pulling forces or tractor beams can pull particles against light propagation by redirecting the incident photons forward. This is typically achieved using Bessel beams with very small half-cone angles, which considerably limits its applicability. One can circumvent such issue by using a superposition of plane waves. In order to investigate optical pulling forces exerted by a pair of non-colinear plane waves, we develop a theoretical framework based on Mie theory, Debye potentials and Wigner rotation matrices. We apply this framework to calculate the optical pulling force on metallo-dielectric composite particles, which we put forward as an alternative material platform to optimize and tailor tractor beams. Indeed we demonstrate that by adding a few plasmonic inclusions to low-refractive index dielectric particles of arbitrary sizes, we are able to produce polarization dependent optical pulling forces that cannot occur in the corresponding homogeneous particles. Altogether our findings not only provide innovative theoretical methods to compute optical pulling forces, but also provide new strategies to tailor and optimize them, paving the way to increase their applicability.