Optimizing optical tweezing with directional scattering in composite microspheres

TL;DR

This paper demonstrates a novel method to optimize optical trapping of high-index microspheres by employing directional scattering and zero backward scattering conditions, enabling stable trapping even with aberrations.

Contribution

It introduces a composite microsphere design with silica inclusions in SiC to achieve zero backward scattering, enhancing optical trapping capabilities for high-index materials.

Findings

Stable trapping achieved with composite microspheres.

Zero backward scattering is essential for trapping high-index materials.

Method remains effective despite spherical aberrations.

Abstract

Trapping of microspheres with a single focused laser beam is usually limited to materials with relative refractive indexes slightly larger than one. We show that directional light scattering can be employed to optically trap high-index materials. For this purpose, we propose a material platform to achieve zero backward scattering (ZBS), also known as the first Kerker condition, in a composite media containing spherical inclusions of silica embedded in a SiC microsphere. By tuning the volume filling fraction of inclusions and the microsphere radius, stable trapping can be achieved, provided that ZBS is combined with the condition for destructive interference between the fields reflected at the external and internal interfaces of the microsphere when located at the focal point. We show that our proposal also holds even in the presence of a significant amount of spherical aberration, which is a common condition in most optical tweezers setups. In this case, achieving ZBS is essential for trapping high-index materials.