Abstract
3D optical vortex trapping upon a polystyrene nanoparticle (NP) by a 1D gold dimer array is studied theoretically. The optical force field shows that the trapping mode can be contact or non-contact. For the former, the NP is attracted toward a corresponding dimer. For the latter, it is trapped toward a stagnation point of zero force with a 3D spiral trajectory, revealing optical vortex. Additionally the optical torque causes the NP to transversely spin, even though the system is irradiated by a linearly polarized light. The transverse spin-orbit interaction is manifested from the opposite helicities of the spin and spiral orbit. Along with the growth and decline of optical vortices the trapped NP performs a step-like motion, as the array continuously moves. Our results, in agreement with the previous experiment, identify the role of optical vortex in the near-field trapping of plasmonic nanostructure.
Highlights
On the other hand, the light-matter interaction reveals the optical spin Hall effect, which is associated with the spin-orbit interaction (SOI) or the spin-momentum locking, linking the linear and spin/orbital angular momenta, have drawn lots of attentions recently[27,28,29,30,31,32,33,34,35,36,37,38,39,40]
We theoretically study the plasmon-enhanced trapping of a 1D gold dimer array induced by a normally incident linearly polarized (LP) near infrared (NIR) Gaussian beam to identify the role of 3D optical vortex playing[15]
These typical 3D spiral trajectories of the NP’s center toward the stagnation point manifest the 3D optical vortex caused by the optical force
Summary
The light-matter interaction reveals the optical spin Hall effect, which is associated with the spin-orbit interaction (SOI) or the spin-momentum locking, linking the linear and spin/orbital angular momenta, have drawn lots of attentions recently[27,28,29,30,31,32,33,34,35,36,37,38,39,40]. The transverse SOI was identified via the optomechanical responses of a metallic NP in an evanescent or surface plasmon polarition field[30,31,32,36]. The concept of vortex nanogear transmission has been proposed, which involves strong coupling SOIs of plasmonic dimer array[43,44]. We theoretically study the plasmon-enhanced trapping of a 1D gold dimer array induced by a normally incident linearly polarized (LP) NIR Gaussian beam to identify the role of 3D optical vortex playing[15]. The height of the focal plane and waist of the Gaussian beam with x-polarization are denoted by hf and w0. If we neglect the gravity and buoyancy forces as well as Brownian motion, the speed of a moving NP driven by the optical force will reach the terminal speed as the optical driving force F is balanced by the reactive drag force
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