旋转对称表面等离激元结构中极端局域光场的准正则模式分析  

Quasinormal mode analysis of extremely localized optical field in body-of-revolution plasmonic structures

作　　者：周强 林树培 张朴 陈学文 Zhou Qiang;Lin Shu-Pei;Zhang Pu;Chen Xue-Wen(School of Physics and Center for Quantum Optical Science,Huazhong University of Science and Technology,Wuhan 430074,China)

机构地区：[1]华中科技大学物理学院

出　　处：《物理学报》2019年第14期100-111,共12页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11874166);国家自然科学基金青年科学基金(批准号:11604109)资助的课题~~

摘　　要：金属微纳结构中表面等离激元能够将自由空间光场局域到亚波长甚至纳米尺度,增强光与物质相互作用等各种物理过程,为等离激元光学在诸多领域带来诱人的应用.然而,目前对表面等离激元光学模场的局域性定量描述仍主要基于直观的空间几何尺寸确定的模式体积,并常被用于刻画模场与物质相互作用的强度.本文基于准正则模理论发展了表征表面等离激元结构中光场局域的理论描述方法,并针对两类典型结构的表面等离激元共振进行了系统的模式分析.结果显示表面等离激元共振可由多个本征模式构成,观察到的光场局域是所有模式共同作用的结果,只有当共振对应单一模式时可以用该本征模式的模式体积描述光场局域.最后,基于上述结果,本文探讨了极端局域光场和近来出现的“皮米腔”的光场局域本质.Surface plasmons in metallic nanostructures can confine the optical field within the region of subwavelength, even nanometer scale, and thus enhance the light-matter interaction and other physical processes, which will lead the plasmon optics to possess attractive applications in many areas. However, the" mode volume" often used to characterize field confinement in plasmonic structures is only defined phenomenologically and suffers ambiguity when applied to complex structures. In this work, we develop a theoretical method to characterize the field confinement based on quasi-normal mode analysis. We recognize the fact that a plasmonic resonance may result from many eigen-modes, which together contribute to the observed field confinement. An effective mode volume is introduced for quasi-normal modes and used to characterize the field confinement when the plasmonic resonance is dominated by a single quasi-normal mode. Two typical kinds of plasmonic structures are systematically examined, and the field confinement on the order of 10 nm^3–100 nm^3 is confirmed. In pursuit of the ultimate field confinement, we revisit the so-called "pico-cavity" formed by an atomistic protrusion in the nano gap of the particle-on-mirror configuration. The apparent hot spot is shown to have contributions from several quasi-normal modes. The dominant one exhibits a further squeezed mode volume compared with the scenario without the protrusion, but is still well above 10 nm^3.

关 键 词：光场局域 表面等离激元 准正则模式分析 旋转对称体 

分 类 号：O437[机械工程—光学工程]