Optical Trapping in a Dark Focus

TL;DR

This paper explores the theoretical use of bottle beams, created by superimposing Gaussian and Laguerre-Gauss modes, as optical traps for dielectric particles, including potential applications for trapping living organisms.

Contribution

It introduces a theoretical framework for trapping dielectric particles with dark focus beams and analyzes stability across different particle sizes, proposing an experimental approach for biological applications.

Findings

Stable trapping of larger dielectric particles is possible.

The forces on particles are derived within the dipole approximation.

An experimental setup for trapping living organisms is proposed.

Abstract

The superposition of a Gaussian mode and a Laguerre-Gauss mode with $\ell=0,p\neq0$ generates the so-called bottle beam: a dark focus surrounded by a bright region. In this paper, we theoretically explore the use of bottle beams as an optical trap for dielectric spheres with a refractive index smaller than that of their surrounding medium. The forces acting on a small particle are derived within the dipole approximation and used to simulate the Brownian motion of the particle in the trap. The intermediate regime of particle size is studied numerically and it is found that stable trapping of larger dielectric particles is also possible. Based on the results of the intermediate regime analysis, an experiment aimed at trapping living organisms in the dark focus of a bottle beam is proposed.