Optical forces and optical force categorizations exerted on quadrupoles in the framework of generalized Lorenz-Mie theory

In the framework of a systematic study of the categorization of optical forces in generalized Lorenz-Mie theory, the present paper is devoted to the categorization of forces exerted on quadrupoles and, more importantly, to their explicit expressions in terms of beam shape coefficients (and of Mie coefficients) which allow one to calculate any kind of forces of the categorization in terms of the essential quantities involved in them. Three levels of categorization are presented. The first level, known since decades, distinguishes between mixing forces and recoil forces. The second level distinguishes between gradient and non-gradient forces. Although these non-gradient forces are usually denoted as scattering forces, we argue that a third level may be introduced in which the so-called scattering forces are actually decomposed in scattering forces and non-standard forces, this last distinction having been found necessary in previous studies devoted to electric dipoles, including Rayleigh scattering, and to magnetodielectric small particles.

Automated summary

In this study, the categorization of optical forces in generalized Lorenz-Mie theory is systematically examined. The focus is on the forces exerted on quadrupoles and their explicit expressions in terms of beam shape coefficients and Mie coefficients. The categorization is done at three levels, distinguishing between mixing forces and recoil forces, and between gradient and non-gradient forces. A third level is proposed to further decompose the so-called scattering forces into scattering forces and non-standard forces.