Internal flows and energy circulation in light beams

TL;DR

This paper reviews the internal energy redistribution and flow patterns in monochromatic light beams, analyzing spin and orbital contributions, and their effects on beam behavior and interactions with particles.

Contribution

It provides a comprehensive description of internal energy flows in light beams, including nonparaxial and paraxial fields, and explores spin-orbit interactions and flow singularities.

Findings

Detailed analysis of spin and orbital energy flows.

Insights into energy transport in standard beam models.

Description of spin-orbit interactions during beam focusing.

Abstract

We review optical phenomena associated with the internal energy redistribution which accompany propagation and transformations of monochromatic light fields in homogeneous media. The total energy flow (linear-momentum density, Poynting vector) can be divided into spin part associated with the polarization and orbital part associated with the spatial inhomogeneity. We give general description of the internal flows in the coordinate and momentum (angular spectrum) representations for both nonparaxial and paraxial fields. This enables one to determine local densities and integral values of the spin and orbital angular momenta of the field. We analyse patterns of the internal flows in standard beam models (Gaussian, Laguerre-Gaussian, flat-top beam, etc.), which provide an insightful picture of the energy transport. The emphasize is made to the singular points of the flow fields. We describe the spin-orbit and orbit-orbit interactions in the processes of beam focusing and symmetry breakdown. Finally, we consider how the energy flows manifest themselves in the mechanical action on probing particles and in the transformations of a propagating beam subjected to a transverse perturbation.