Fundamental Limits of Optical Force and Torque

TL;DR

This paper investigates the fundamental upper limits of optical force and torque exerted by plane wave illumination on particles, deriving bounds for different interaction channels and illustrating how these can be maximized for various applications.

Contribution

It analytically derives upper bounds for optical force and torque contributions from different light-matter interaction channels on isotropic particles.

Findings

Derived analytical upper bounds for optical force and torque.

Identified how different interaction channels contribute to maximum force and torque.

Provided examples of particles achieving these bounds.

Abstract

Optical force and torque provide unprecedented control on the spatial motion of small particles. A valid scientific question, that has many practical implications, concerns the existence of fundamental upper bounds for the achievable force and torque exerted by a plane wave illumination with a given intensity. Here, while studying isotropic particles, we show that different light-matter interaction channels contribute to the exerted force and torque; and analytically derive upper bounds for each of the contributions. Specific examples for particles that achieve those upper bounds are provided. We study how and to which extent different contributions can add up to result in the maximum optical force and torque. Our insights are important for applications ranging from molecular sorting, particle manipulation, nanorobotics up to ambitious projects such as laser-propelled spaceships.