Optical trapping of anti-reflection coating-coated spheres

TL;DR

This paper demonstrates that anti-reflection coatings on spheres can enhance optical trapping by reducing scattering and increasing gradient forces, with theoretical and experimental validation focusing on spherical particles and specific beam conditions.

Contribution

It provides a rigorous analysis of how anti-reflection coatings improve optical trapping by reducing backward scattering and increasing gradient forces, supported by both theory and experiments.

Findings

Anti-reflection coating reduces backward scattering.

Coating enhances gradient force by increasing particle size.

The approach is effective only for spherical particles with aplanatic beams.

Abstract

It was theoretically proposed and experimentally demonstrated that anti-reflection coating allows one to trap a high dielectric sphere, at the same time enhancing the transverse optical force. Here, by explicitly calculating the gradient force and the scattering force, we rigorously show that these were mainly consequences of the reduction in scattering force due to the suppression of backward scattering, and enhancement in gradient force due to the increased in overall particle size. The reduction of scattering force can be understood within a ray optics theory and also the Mie theory. The coating approach only works for a spherical particle trapped by an aplanatic beam, and it does not work in general.