光波纳米推进技术中的表面等离激元增益光镊作用机理

Mechanisms of Optical Tweezing Enhancement by Surface Plasmon Polariton in Plasmon Force Propulsion Technology

关键词:  光波纳米推进  表面等离激元  光镊作用  数值计算  粒子图像测速试验

Key words:  Plasmonic force propulsion  Surface plasmon polariton  Optical tweezing effect  Numerical calculation  Particle image velocimetry test

摘要:

为研究天线不同结构对表面等离激元（SPP）增益光镊作用的影响，建立天线-基底的电磁波传输耦合激元电场触发光梯度力的数值模型，并利用数值模型分析天线不同结构对SPP电场的影响规律，同时，这种电场变化规律对光镊增益有直接的数学关系，基于上述物理机制，获得不同天线结构对光梯度力产生的优化策略。为验证上述物理机制与优化策略的有效性，开展纳米颗粒的粒子图像测速（PIV）试验，天线材料为银，基底为二氧化硅，纳米颗粒为银，试验能够完好地观测到纳米颗粒在天线通道的运动情况。结果表明，光梯度力的增益机制在于激元电场强度和梯度两方面因素，前者随天线不对称性增强而先增大后减小，后者呈现一直增大趋势；纳米颗粒推动作用力的计算误差约为5.5%~13.8%，且试验值与计算值的趋势相符，一方面验证本文研究机理及优化策略的有效性，另一方面证明PFP技术的原理可行。

Abstract:

The enhancement of the optical tweezing by the surface plasmon polariton （SPP） has played an important role in the performance improvement of the plasmon force propulsion （PFP） technology. In order to study the effects of the antenna configurations on the optical tweezing enhancement by the SPP， a numerical model to solve the electromagnetic wave transmission and the optical gradient force induced by the SPP field has been established. Based on this model， the pattern of the SPP electric field under different antenna configuration was analyzed numerically， and a direct mathematical relationship was built between the SPP field pattern and the optical tweezing effect. According to the mechanism above， the optimization strategy of the optical gradient force under different antenna configurations was obtained. A nano-particle image velocimetry test was conducted to verify the mechanism and optimization strategy proposed by the present study. The antenna material was Ag， the substrate material was SiO₂， and the nano-particle material was Ag. The transportation of the nano-particle along the antenna channel could be clearly observed by the PIV test. The main conclusion shows as follow： （1） The enhancement mechanism of the optical gradient force is associated with two parameters， the SPP electric field intensity and the gradient of the field intensity. With the asymmetry of the antenna structure increasing， the former parameter increases first and then decreases， and the latter parameter is growing all the time. （2） The calculation error of the push force of the nano-particle ranges from 5.5% to 13.8% approximately， and the calculation results are consistent with the measuring results. On one hand， the mechanism and optimization strategy proposed by the present study can be validated； on the other hand， the PFP technology can be proved feasible.