Tailoring optical pulling forces with composite microspheres
Rfaqat Ali, F. A. Pinheiro, R. S. Dutra, Paulo A. Maia Neto
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 their applicability. One can circumvent such an issue by using a superposition of plane waves. In order to investigate optical pulling forces exerted by a pair of noncollinear 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 metallodielectric 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 strategies to tailor and optimize them, paving the way to increase their applicability.