Enhanced optical trapping assisted by resonant energy backflow in a perforated dielectric microsphere

TL;DR

This paper demonstrates that a perforated dielectric microsphere with resonant whispering-gallery modes can significantly enhance optical trapping forces by isolating energy backflow regions, making it an efficient optical tweezer.

Contribution

It introduces a perforated microsphere design that isolates energy backflow regions, enhancing optical trapping via resonant WGMs, which is a novel approach for improved nanoobject manipulation.

Findings

Resonant WGMs induce regions of reverse energy flow in the microsphere.

A perforated design isolates backflow regions, boosting optical forces.

The perforated microsphere acts as an efficient optical tweezer.

Abstract

Optical energy flow inside a dielectric microsphere exposed to an optical wave is usually codirected with its wave vector. At the same time, if the optical field in a microparticle is in resonance with a high-quality spatial eigenmode, referred to as the whispering-gallery mode (WGM), at least two regions of reverse energy flow emerge in the illuminated and shadow particle hemispheres. These areas are of considerable practical interest due to their enhanced optical trapping potential provided they should be previously cleared from particle material. In this paper, we consider a perforated microsphere with an air-filled pinhole fabricated along the particle diameter and theoretically analyze the conditions for WGMs excitation. A pinhole isolates the energy backflow regions of WGM and multiple enhances the optical pull-in force that transforms a perforated microsphere into an efficient optical tweezer for trapping various nanoobjects.