Radiation force and torque of light-sheets illuminating a cylindrical particle of arbitrary geometrical cross-section exhibiting circular dichroism

Abstract

Unlike standard dielectric materials, the interaction of light-sheets of arbitrary wavefronts with a particle exhibiting circular dichroism, such as chiral, topological insulator, liquid crystal, or metamaterials to name a few examples, requires additional fundamental developments from the standpoint of scattering, radiation force and torque theories.The purpose of this work is therefore directed toward developing an exact analytical formalism applicable to a 2D object exhibiting TM ⇄ TE mode conversion and possessing an arbitrary geometrical cross-section. Exact mathematical expressions for the longitudinal and transverse optical radiation force and axial torque components are derived stemming from series expansions for the incident and scattered electromagnetic fields using the mode matching method in cylindrical coordinates. The generalized radiation force and torque expressions depend on the beam-shape coefficients (BSCs) of the incident light-sheet, and the scattering coefficients of the object. Extra new terms describing the generation of the scattered cross-polarized waves induced due to TM ⇄ TE mode conversion contribute to the radiation force and torque series. Numerical illustrative examples for a circular lossy electromagnetic conductor (LEMC) cylinder are provided assuming illumination by various wavefronts, ranging from plane progressive, standing and quasi-standing waves to other non-paraxial Airy light-sheets with linear and circular polarization. In essence, the present theoretical formalism provides a complete analysis in the framework of the generalized Lorenz–Mie theory in 2D for any particle exhibiting circular dichroism in any structured light-sheet. Potential applications are in the design, optimization and the numerical predictions and computation of the optical radiation force and torque for particle transport and rotation in the realm of optical tweezers, particle manipulation and stabilization. Some perspectives are discussed and replies to misleading comments made in the literature on the publication [F.G. Mitri, J Quant Spectro Rad Transf 2020;250:106994] given by Ref. [33] are provided.