Optical trapping characteristics of a metal microsphere coated with thick dielectric shell in the focused optical field

The scattering, gradient and net forces exerted on the metallic microspheres with the thick shell were calculated and the axial trapping force exerted on the oxidized copper microspheres with a force model were analyzed for a single-beam gradient trap on a core-shell (metal/dielectric) microsphere. Unlike the case for a purely metallic Mie particle, a metallic microsphere with thick dielectric shell can be trapped easily, but not be trapped in the high intensity region of focused beam. In the experiment the copper microparticles coated with copper oxide can be trapped in the focused Gaussian beam and also transported horizontally. The optical characteristics of core-shell structured metal particles could be analyzed with the theoretical analysis and experimental results, which extend the applications of optical tweezers.