Optical momentum distributions in monochromatic, isotropic random vector fields

TL;DR

This paper analyzes how electromagnetic energy flows in complex random light fields by decomposing the Poynting momentum into orbital and spin parts, revealing their similar distributions and distinct spatial organizations.

Contribution

It provides a detailed analytical and numerical study of optical momentum decomposition in isotropic random fields, highlighting differences from paraxial cases and extending to helicity-specific fields.

Findings

Orbital and spin momenta are identically distributed in magnitude in isotropic random fields.

Orbital currents form broad unidirectional channels, while spin currents show vorticity and rapid directional changes.

Results extend to fields with pure helicity, emphasizing electric-magnetic symmetry in optical momenta.

Abstract

We investigate the decomposition of the electromagnetic Poynting momentum density in three-dimensional random monochromatic fields into orbital and spin parts, using analytical and numerical methods. In sharp contrast with the paraxial case, the orbital and spin momenta in isotropic random fields are found to be identically distributed in magnitude, increasing the discrepancy between the Poynting and orbital pictures of energy flow. Spatial correlation functions reveal differences in the generic organization of different optical momenta in complex natural light fields, with the orbital current typically forming broad channels of unidirectional flow, and the spin current manifesting larger vorticity and changing direction over subwavelength distances. These results are extended to random fields with pure helicity, in relation to the inclusion of electric-magnetic democracy in the definition of optical momenta.