基于有限元算法和Maxwell应力张量法, 分析了紧聚焦高斯光束照明下金基底表面的金纳米球所受光力。利用无结构的平整金基底, 被捕获的金纳米颗粒和金基底之间能够产生间隙表面等离激元和局域表面等离激元共振效应, 将电磁场局域在金球与金基底之间的纳米间隙内, 增强了金纳米球所受光力以及光阱刚度。通过研究入射光的偏振态、金纳米球的半径、基底类型以及聚焦光束焦点到基底表面距离对光力的影响, 得到了实现基底附近金纳米球稳定捕获以及获得最大光力的优化方案。

The optical force and optical trap stiffness of an Au nanosphere near the Au substrate under the illumination of a tightly focused Gaussian beam were calculated with the finite element method and the Maxwell’s stress tensor. By utilizing the GSPP excited in the Au nanosphere-substrate nano-gap combined with the localized surface plasmon resonance (LSPR) of the Au nanosphere, the electromagnetic field localized in the gap was drastically enhanced which results in an enhanced optical force and optical trap stiffness exerted on the nanosphere. By investigating the impact of the polarization state of the incident light, the radius of the gold nanosphere, the type of the substrate and the defocusing amount of the focused beam on the optical force, an optimal scheme for achieving stable capture of the gold nanosphere near the substrate and obtaining the strongest optical force was obtained.