# Non-intuitive Computational Optimization of Illumination Patterns for Maximum Optical Force and Torque

## TL;DR

This paper presents a numerical framework for designing structured illumination to significantly enhance optical force and torque on micro- and nano-scale objects, outperforming traditional methods.

## Contribution

It introduces a novel computational approach combining Bessel basis, boundary element method, and local optimization for optimized illumination design.

## Key findings

- Achieved 20-fold increase in optical torque compared to circular polarization.
- Demonstrated effectiveness across 2000 random initial configurations.
- Analyzed the impact of multipolar plasmon resonances on force and torque enhancement.

## Abstract

This paper aims to maximize optical force and torque on arbitrary micro- and nano-scale objects using numerically optimized structured illumination. By developing a numerical framework for computer-automated design of 3d vector-field illumination, we demonstrate a 20-fold enhancement in optical torque per intensity over circularly polarized plane wave on a model plasmonic particle. The nonconvex optimization is efficiently performed by combining a compact cylindrical Bessel basis representation with a fast boundary element method and a standard derivative-free, local optimization algorithm. We analyze the optimization results for 2000 random initial configurations, discuss the tradeoff between robustness and enhancement, and compare the different effects of multipolar plasmon resonances on enhancing force and torque. All results are obtained using open-source computational software available online.