Lagrangian PAFs in multiple optical scattering by two absorptive dielectric parallel cylinders

Abstract

The objective of this work is to derive semi-analytical integral expressions for the Lagrangian longitudinal (L) and transverse (T) photophoretic asymmetry factors (PAFs) for an aggregate pair of parallel absorptive dielectric cylinders of arbitrary radii in plane waves with arbitrary incidence angles and polarizations. Based on the multiple scattering theory of waves and its rigorous mathematical formalism, the components of the internal electric field vectors in cylindrical coordinates are determined and used subsequently to compute the PAFs. The L- and T-PAFs are directly proportional to the L and T components of the photophoretic (known also as radiometric) force vector, respectively, induced by light absorption inside each dielectric cylinder. The modal expansion method in cylindrical coordinates and adequate boundary matching at the surface of each particle are used to determine the internal coefficients to compute the PAFs. Subsequently, the integral expressions are derived and evaluated assuming TE- and TM-polarized plane waves with arbitrary angles in the polar plane. Additional computations for the dimensionless intensity function are performed, and the corresponding results provide quantitative assessment of the internal heated portions of the absorptive dielectric cylinders at different interparticle distances while illuminated by plane waves with variable incidence angles and polarizations. The results are of some importance in electromagnetic/optical multiple scattering theory and related applications in optical binding, optical tweezers, particle manipulation, and photophoresis.