Influence of absorption on optical trapping force of spherical particles in a focused Gaussian beam

Based on the extended geometrical optics model, a theoretical study of the optical trapping force on a spherical particle with the absorption considered is presented. In this study, the numerical simulation on transverse trapping force is given. The results suggest that the absorption coefficient and the axial shift of the particle center from the focused Gaussian beam waist greatly influence the trapping properties. Spherical particles with weak absorption could be stably trapped on the optical axis of the Gaussian beam, and the stiffness of trapping decreases with the increasing absorption coefficient of the particle. A highly absorbing particle has more complex trapping characteristics. As the particle location changes from the upstream to the downstream direction of the beam, the stable trapping position may firstly locate on the beam axis, secondly be along a circular route centered on the beam axis, and finally vanish. If the stable trapping position is along a circular route, the stiffness of trapping increases with the increasing absorption coefficient.