Scattering of inhomogeneous circularly polarized optical field and mechanical manifestation of the internal energy flows

TL;DR

This paper investigates how inhomogeneous circularly polarized light interacts with spherical particles, revealing the distinct mechanical effects of spin and orbital energy flows through numerical analysis based on Mie theory.

Contribution

It provides a detailed numerical analysis of the mechanical effects of spin and orbital energy flows in inhomogeneous circularly polarized light on spherical particles, highlighting their different scaling behaviors.

Findings

Transverse forces depend on particle size and type, with specific power-law behaviors.

Asymmetry in forward and backward momentum fluxes is linked to spin energy flow.

Distinct mechanisms (dipole and non-dipole) govern the forces from spin and orbital flows.

Abstract

Based on the Mie theory and on the incident beam model via superposition of two plane waves, we analyze numerically the momentum flux of the field scattered by a spherical microparticle placed within the spatially inhomogeneous circularly polarized paraxial light beam. The asymmetry between the forward- and backward-scattered momentum fluxes in the Rayleigh scattering regime appears due to the spin part of the internal energy flow in the incident beam. The transverse ponderomotive forces exerted on dielectric and conducting particles of different sizes are calculated and special features of the mechanical actions produced by the spin and orbital parts of the internal energy flow are recognized. In particular, the transverse orbital flow exerts the transverse force that grows as a^3 for conducting and as a^6 for dielectric subwavelength particle with radius a, in compliance with the dipole mechanism of the field-particle interaction; the force associated with the spin flow behaves as a^8 in both cases, which testifies for the non-dipole mechanism. The results can be used for experimental identification and separate investigation of the spin and orbital parts of the internal energy flow in light fields.