光子角动量在环形金属纳米孔异常透射过程中的作用

Role of optical angular momentum in enhanced transmission process of plasmonic coaxial nanoring aperture

在环形凹槽包围环形金属纳米孔的异常透射器件的研究中,环形凹槽可以将携带光子角动量的入射光转化为涡旋表面等离极化激元,这些涡旋表面等离极化激元传向几何中心并与直接照射在环形纳米孔上的光子发生干涉,当相互干涉的光子满足相位匹配条件时,环形纳米孔的透射率得到显著增强.本文利用理论分析和数值计算的方法研究了光子角动量和凹槽半径对环形纳米孔透射过程的影响.我们发现调节环形凹槽的半径和入射光携带的光子角动量可以调节光子在金膜上表面传输时的径向传播相位,进而影响了环形纳米孔附近的干涉电场强度,最终决定了环形纳米孔的透射率,进而可以通过调节凹槽的半径来调节携带不同光子角动量的光束在环形纳米孔的透射率.本文的研究结果对基于涡旋表面等离极化激元的异常透射器件的设计具有重要的指导意义.

The nano groove can highly improve the transmittance of coaxial nanoring aperture due to the excitation of surface plasmon polariton(SPP).The total angular momentum carried by incident beam is reserved in the whole process and transferred to the SPP,thus the vortex SPP carrying orbital angular momentum is generated.The enhanced transmittance of nano aperture by vortex SPP has a wide range of applications,but its physical mechanism has been ignored for a long time.Here we study the process of the enhanced transmittance of the coaxial nanoring aperture and provide a model to describe the process of photon transmission.When the incident light irradiates on the coaxial nanoring aperture and nano groove,the vortex SPP induced by the groove propagates to coaxial nanoring aperture.Some of the photons in the SPP are coupled into the coaxial nanoring aperture and some are reflected back.The reflected photons travel back and forth multiple times between the coaxial nanoring aperture and nano groove.The vortex SPP interacts with the incident beam at the round of coaxial nanoring aperture,which determines the intensity at the round of the coaxial nano aperture,and thus affecting the transmittance.We systematically study the influence of optical angular momentum and the radius of the nano groove on the transmittance of coaxial nanoring aperture by using theoretical analysis and numerical simulations.The results show that the optical angular momentum and radius of the nano groove both affect the radial propagation phase of vortex SPP from nano groove to coaxial nanoring aperture,hence affecting the intensity of the electric field at the round of coaxial nanoring aperture and consequently determine the transmittance.The transmittance peaks of incident beams with different optical angular momenta will appear at different radii of the nano grooves,which provides a potential way to modulate the transmittance by adjusting the radius of the nano groove.This study is instructive for designing the enhanced optical transmission nano device based on vortex SPP.