Orbital analysis of single nanoparticle in-plane motion driven by an optical vortex

Quantitative evaluation of optical forces on nanoscale objects caused by optical vortices is significant for application of optical vortex to nanotechnology. In this study, we analyze an orbital motion of single gold nanoparticles with a diameter of 150 nm driven by the Laguerre-Gaussian beam. A nanofluidic channel with a height of 300 nm is used to confine the orbital motion into two-dimensional plane by restricting their Brownian motion perpendicular to a focal plane of objective lens, resulting in the visualization by dark-field microscopy. A particle tracking analysis of the acquired images allows the quantitative evaluation of optical forces, such as trapping stiffness and driving force of the orbital motion, and show a reasonable agreement with a theoretical estimation.