Rotation of an elliptical dielectric particle in the focus of a circularly polarized Gaussian beam

A force and a torque exerted on an elliptical dielectric particle in the focus of a spherical circularly polarized laser beam are considered. The numerical simulation is conducted using a diffraction field obtained by an FDTD method, with the force and torque derived using a Maxwell’s stress tensor. It is shown that an optical torque is exerted on the center of an elliptical particle put in the focus of a circularly polarized spherical wave, making it rotate around the optical axis. The rotation occurs when the elliptical microparticle is situated in a transverse plane to the optical axis. When shifting the ellipsoid from the optical axis, an optical trapping force appears that prevents its displacement, meaning that the particle finds itself in an optical trap on the optical axis.