# Optical trapping below the diffraction limit with a tunable beam waist using super-oscillating beams

## TL;DR

This paper demonstrates how super-oscillating beams can create sub-diffraction light spots for enhanced optical trapping, with trap stiffness depending non-monotonically on particle-to-beam size ratio, optimizing trapping conditions.

## Contribution

It introduces a tunable beam waist technique using super-oscillating beams for improved sub-diffraction optical trapping and analyzes the effect of particle size on trap performance.

## Key findings

- Optimal trapping occurs when particle size exceeds beam waist but avoids the side ring.
- Trap stiffness varies non-monotonically with particle-to-beam size ratio.
- Super-oscillating beams outperform regular traps in localization of submicron particles.

## Abstract

Super-oscillating beams can be used to create light spots whose size is below the diffraction limit with a side ring of high intensity adjacent to them. Optical traps made of the super-oscillating part of such beams exhibit superior localization of submicron beads compared to regular optical traps. Here we focus on the effect of the ratio of particle size to trap size on the localization and stiffness of optical traps made of super-oscillating beams. We find a non-monotonic dependence of trapping stiffness on the ratio of particle size to beam size. Optimal trapping is achieved when the particle is larger than the beam waist of the superoscillating feature but small enough not to overlap with the side ring.