paper

Internal flows and energy circulation in light beams

arXiv:1011.0862 · doi:10.1088/2040-8978/13/5/053001

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.

50 pages, 21 figs, 173 refs. The final version of manuscript (v1) is modified according to the referee's remarks and recent data. Main changes: additional discussion of the energy flows in Bessel beams (section 4.1), new refs, Conclusion shortened and made more accurate. 01.11.2023: Eq. (4.5) corrected. 22.02.2026: Eq. (3.38), Fig. 2b and its caption corrected, a note added beneath (6.25)

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