Optical radiation force on a perfect electromagnetic conductor (PEMC) sphere

Abstract

This work extends the scope of the previous study on the electromagnetic radiation force on a perfect electromagnetic conductor (PEMC) cylinder [F.G. Mitri, J. Quant. Spectr. Rad. Transfer, 233 (2019) 21–28] to the case of a sphere of arbitrary size, illuminated by linearly-polarized plane progressive waves. In contrast with the PEMC cylinder case, the analysis shows that the effect of the cross-polarized waves compensates that of the co-polarized waves such that the optical radiation force is unaffected by the change of the electromagnetic admittance parameter M of the sphere. The multipole series expansion method in spherical coordinates is used to derive exact mathematical series for the co-polarized and cross-polarized components of the longitudinal radiation force. Numerical results for the radiation force efficiency and its co-polarized and cross-polarized components demonstrate the individual contributions. The results show that the cross-polarized component of the radiation force efficiency can be positive or negative as the dimensionless size ka varies. Moreover, it vanishes for ka ≈ 1.78 regardless of the admittance parameter of the PEMC sphere. Notice that the total force (i.e. the sum of the co-polarized and cross-polarized components) is always repulsive (i.e., positive). It is also verified that the results are in complete agreement with the law of energy conservation applied to scattering, where the extinction and scattering energy efficiencies are equal, and independent of M. Furthermore, an equivalent expression for the longitudinal radiation force efficiency is derived stemming from an analysis of the asymmetry parameter and the law of energy conservation applied to scattering. Additional computations for the co-polarized and cross-polarized components of the scattering asymmetry parameter are presented and discussed. The results are of some importance from the standpoint of the basics of the electromagnetic radiation force theory and related applications in particle manipulation.