Optical Angular Momentum in Classical Electrodynamics

TL;DR

This paper explores the nature of electromagnetic angular momentum in classical electrodynamics, demonstrating its relationship with energy, mechanical effects, and particle interactions through simple examples.

Contribution

It provides a detailed analysis of electromagnetic angular momentum using Maxwell's equations and illustrates its physical implications and interactions.

Findings

EM energy and angular momentum are closely related.

Radiating EM angular momentum results in mechanical momentum transfer.

Spin and orbital angular momenta induce different responses in particles.

Abstract

Invoking Maxwell's classical equations in conjunction with expressions for the electromagnetic (EM) energy, momentum, force, and torque, we use a few simple examples to demonstrate the nature of the EM angular momentum. The energy and the angular momentum of an EM field will be shown to have an intimate relationship; a source radiating EM angular momentum will, of necessity, pick up an equal but opposite amount of mechanical angular momentum; and the spin and orbital angular momenta of the EM field, when absorbed by a small particle, will be seen to elicit different responses from the particle.