Anapole-Assisted Low-Power Optical Trapping

Abstract

Low-power optical trapping of nanoscale objects is important for nanoscience and life science research. In the previous researches, plasmonic nanoantennas has been demonstrated to provide spatially confined and enhanced electromagnetic fields, which generates strong optical force on nanoscale objects. However, they suffer from loss-induced heating effect. On the other hand, dielectric structure can provide low heating affect due to the nature of low loss but experience the problem of moderate light intensity enhancement. To address the problems of the dielectric as well as taking its advantage, this thesis reports a dielectric-metal hybrid nanoantenna system supporting non-radiating anapole modes that provides high electric field enhancements at a region spatially dislocated away from the high temperature region. The adjacent temperature rise in the metal region can be used to induce long-range electrothermoplasmonic flow on-demand with velocities of up to 100 um/s to rapidly transport target objects towards the electromagnetic hotspot of the anapole nanoantenna. Furthermore, the thesis shows the enhanced optical force and trapping potential in the dielectric nanoantenna system on sub-100 nm size nanoscale objects. This enhanced optical force combined with a positive thermophoretic force directed towards the dielectric region provides record metrics for high stability trapping of nanoscale objects.