Optical spin precession

TL;DR

This paper extends the concept of optical spin angular momentum to non-monochromatic fields, revealing precessional dynamics analogous to magnetization behavior, with implications for light-matter interactions.

Contribution

It introduces a new formulation of optical spin for non-monochromatic fields and uncovers their precessional dynamics, previously unexplored in this context.

Findings

Discovered precessional dynamics of electromagnetic spin in polychromatic fields.

Formulated a Landau-Lifshitz-like equation for optical spin dynamics.

Demonstrated the parallel between photonic spin and magnetization dynamics.

Abstract

Period-averaged electromagnetic spin angular momentum is a well-established quantity for monochromatic fields, governing phenomena such as light-matter interactions with chiral particles and spin-orbit coupling effects. In contrast, the spin angular momentum of non-monochromatic fields remains unexplored. Here, we extend the concept of optical spin to the domain of non-monochromatic electromagnetic fields. Through this formulation, we uncover the precessional dynamics of electromagnetic spin in specific polychromatic configurations, including the superposition of circularly and linearly polarized plane waves propagating orthogonally at different frequencies, as well as fields generated by a precessing magnetic dipole. We discover that the dynamics of the electromagnetic spin in these cases obeys a Landau-Lifshitz-like equation establishing a profound parallel between dynamics of magnetization and photonic spin.