Optical pulling forces enhancement through near field and momentum based on the coupling of borophene and metal surface plasmon polariton resonances

Abstract

Backward optical pulling force (BOPF) has gained much attention due to flexible optical manipulation compared to forward optical pushing force (FOPF). A multilayer borophene-dielectric-metal structure was designed to enhance electric field intensity and photonic momentum change, achieving the BOPF enhancement on gold nanowires. In the structure, the excitation of borophene plasmon polaritons (BSPs) is a key to improving BOPF. The electric intensity is enhanced by the strong coupling between BSP and cavity resonance modes. The resonances of coupled modes generate radiation, resulting in a longitudinal force $F_y$. When the BSPs were excited by oblique incidence light, lateral momentum $\hslash k_x$ was generated, resulting in a lateral BOPF $F_x$. Both the longitudinal force $F_y$ and lateral force $F_x$ were enhanced by the strong coupling resonances. Moreover, metal surface plasmon polaritons (MSPPs) were excited by the periodic grating in the structure. When the negative MSPP mode coincides with the BSP modes, the coupling between them is generated through the scattering of the gold nanowire, resulting in a large photonic momentum increment (the sum of the momenta of BSP and MSPP, $\hslash k_{BSP}+\hslash k_{MSPP}$). Based on the conservation of momentum, the lateral BOPF was enhanced extremely. The switching between lateral FOPF and BOPF is achieved by the exchange between MSPP and BSP. The BOPF enhancement has important applications in light-matter interaction techniques, such as signal processing, particle trapping, and optical tweezers.