Numerical Study on Dynamical Behavior of Nanoparticles in Optical Vortex

摘要

When nanoparticles are exposed to an optical field with orbital angular momentum, that is optical vortex, such particles are swirled around optical axis. Although such a phenomenon was observed experimentally, theoretical and numerical approaches have not been developed enough. In this study, we propose a numerical model for dynamical motions of a single nanoparticle. Based on Rayleigh scattering regime, the gradient force which dominantly acts on a nanoparticle is computed. The gradient force is usually derived from time averaged electric field and then, a tangential component is vanished. Herein, we carefully treat the tangential term by using time dependent electromagnetic fields. Consequently, it is found that a tangential component in the gradient force induce swirling motions of a nanoparticle.