金属基底上光学偶极纳米天线的自发辐射宽带增强:表面等离激元直观模型  

Broadband enhancement of spontaneous emission by optical dipole nanoantenna on metallic substrate:An intuitive model of surface plasmon polariton

作　　者：张炼 王化雨 王宁 陶灿[1,2] 翟学琳 马平准 钟莹 刘海涛[1,2] Zhang Lian;Wang Hua-Yu;Wang Ning;Tao Can;Zhai Xue-Lin;Ma Ping-Zhun;Zhong Ying;Liu Hai-Tao(Institute of Modern Optics,College of Electronic Information and Optical Engineering,Nankai University,Tianjin 300350,China;Tianjin Key Laboratory of Micro-scale Optical Information Science and Technology,Nankai University,Tianjin 300350,China;College of Physics and Electronic Engineering,Zhengzhou Normal University,Zhengzhou 450044,China;State Key Laboratory of Precision Measurement Technology and Instruments,School of Precision Instrument and Opto-Electronics Engineering,Tianjin University,Tianjin 300072,China)

机构地区：[1]南开大学电子信息与光学工程学院,现代光学研究所,天津300350 [2]南开大学,天津市微尺度光学信息技术科学重点实验室,天津300350 [3]郑州师范学院物理与电子工程学院,郑州450044 [4]天津大学精密仪器与光电子工程学院,精密测试技术及仪器国家重点实验室,天津300072

出　　处：《物理学报》2022年第11期341-355,共15页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:62075104,61775105)资助的课题.

摘　　要：本文提出一种具有宽波段自发辐射增强性能的金属基底上光学偶极纳米天线,实现的总辐射速率与远场辐射速率增强因子分别达到5454和1041,在近红外波段,自发辐射增强(Purcell因子超过1000)波长范围达到260 nm,并且能够实现远场定向辐射.为了阐明天线性能背后的物理机制,本文考虑天线臂上表面等离激元激发和多重散射的直观物理过程,基于Maxwell方程组第一性原理,建立了一个半解析模型,能够全面复现天线的辐射特性,包括总辐射速率、远场辐射速率、远场辐射方向图等.该模型提供了一个直观的物理图像,即在模型导出的两个相位匹配条件下,表面等离激元在天线臂上形成了一对Fabry-Perot共振获得增强,然后传播到纳米间隙内点辐射源位置和散射到自由空间,由此分别提高了总辐射速率和远场辐射速率.并且,这一对Fabry-Perot共振产生了一对相互靠近的谐振峰,由此形成了宽波段自发辐射增强.本文提出的偶极纳米天线可以应用于荧光增强、拉曼散射增强及高速、高亮度纳米光源等领域,所提出的模型可用于光学天线的物理理解和直观设计.Optical nanoantennas can achieve electromagnetic-field enhancement under far-field excitation or spontaneous-emission enhancement under excitation by radiating emitters.Among them,nanoantennas on a metallic substrate(i.e.the so-called nanoparticle-on-mirror antennas)have aroused great research interest due to their ease in forming metallic gaps of sizes down to a few nanometers or even subnanometer.Here we propose an optical dipole nanoantenna on a metallic substrate with a broadband enhancement of spontaneous emission.Its total and radiative emission-rate enhancement factors can reach up to 5454 and 1041,respectively.In the near-infrared band,the wavelength range of spontaneous-emission enhancement(Purcell factor over 1000)can reach 260nm.By changing the width of the slit between the two antenna arms and also the length of the antenna arms,the spontaneous-emission enhancement bandwidth and enhancement factors can be adjusted,respectively,which brings great freedom and simplicity to the design process.The antenna can achieve a strong far-field radiation within a central anglular zone(polar angleθ≤60°)corresponding to a certain numerical aperture of objective lens,and therefore can increase the intensity of the fluorescence collected by the objective lens.Based on the above performances,the antenna can provide a broadband enhancement of spontaneous emission for fluorescent molecules or quantum dots(whose fluorescence spectrum usually covers a certain wavelength range),which is of great significance for the applications such as in high-speed and super-bright nanoscale light sources and high-sensitivity fluorescent-molecule sensing.To clarify the underlying physical mechanisms,we build up a semi-analytical model by considering an intuitive excitation and multiple-scattering process of surface plasmon polaritons(SPPs)that propagate along the antenna arms.All the parameters used in the model(such as the SPP scattering coefficients)are obtained via rigorous calculations based on the first principle of Maxwell's equ

关 键 词：光学纳米天线 /自发辐射增强 /表面等离激元 /半解析模型 

分 类 号：TN820[电子电信—信息与通信工程]