Whispering-gallery modes promote enhanced optical backflow in a perforated dielectric microsphere

TL;DR

This paper investigates how whispering-gallery modes in a perforated dielectric microsphere can enhance optical backflow, revealing new ways to manipulate energy flow for improved optical trapping.

Contribution

It introduces a perforated microsphere with a pinhole that isolates and enhances optical backflow, enabling more efficient optical tweezers.

Findings

Multiple enhancement of backflow intensity at WGM resonance

Pinhole isolates energy backflow region

Perforated microsphere acts as an efficient optical tweezer

Abstract

Optical energy flow inside a dielectric microsphere is usually codirected with the optical wavevector. At the same time, if the optical field in a microsphere is in resonance with one of the high-quality spatial eigenmodes (whispering-gallery modes - WGMs), a region of reverse energy flow emerges in the shadow hemisphere. This area is of considerable practical interest due to increased optical trapping potential. In this Letter, we consider a perforated microsphere with an air-filled single pinhole fabricated along the particle diameter and numerically analyze the peculiarities of WGM excitation in a nanostructured microsphere. A pinhole isolates the energy backflow region of a resonant mode and changes a perforated microsphere into an efficient optical tweezer. For the first time to our knowledge, we reveal the multiple enhancement of backflow intensity in the pinhole at a WGM resonance and discuss the way for its manipulation.