基于频域有限差分法的二维自发辐射特性研究

原子自发辐射效率的提高对单光子源等光电子设备的研究和制造具有重要的意义.本文推导了自发辐射率和局域态密度的格林函数表示形式,通过频域有限差分法求解格林函数,得到自发辐射率的数值特性.分析了在不同金属材料、结构以及辐射波长下的自发辐射率,探讨了其内在的物理机理,结果表明:特定波长下介质的表面等离激元效应会增强自发辐射,不同材料和结构对辐射效率的提高有不同的影响.该研究结果可为新型纳米器件及光电子设备的制造以及优化提供重要的参考.     

柱状磁光颗粒的局域表面等离激元共振及尺寸效应

柱状磁光颗粒的局域表面等离激元共振为二维磁光光子晶体的手征性边缘模的生成提供了重要的机制. 但目前对此类颗粒的局域表面等离激元共振效应的研究局限于长波长近似下的结果, 且缺乏对发生共振时的远场与近场特征的深入了解. 本文从散射理论出发, 计算并分析了柱状磁光颗粒发生局域表面等离激元共振的条件与特殊的场特征, 并讨论了颗粒尺寸对共振峰的影响. 计算结果解释了实验中观察到的二维磁光光子晶体的共振带隙与在长波长近似下得到的局域表面等离激元共振频率的明显偏移, 并展示了颗粒在较大尺寸下形成的高阶共振峰, 这可能有助于利用共振效应在磁光光子晶体中实现多模的手征边缘态.     

局域表面等离激元

局域表面等离激元使得贵金属纳米颗粒具有丰富的光学性质,其应用涵盖能源、生物医学、安全、信息、超材料等诸多领域。文章简要介绍局域表面等离激元的基本性质、贵金属纳米结构中的局域表面等离激元共振耦合以及具有局域表面等离激元特性的贵金属纳米结构的一些重要应用。     

银纳米圆盘光天线的远场方向性研究

采用时域有限差分方法计算了银纳米圆盘光天线模型的场分布,研究了光偶极天线的远场辐射特性随距离和厚度、半径变化的规律以及影响其远场方向性的因素.研究发现,偶极子垂直放置在银纳米圆盘下方一定距离时,银盘厚度和半径的改变均可使方向性图中出现新的辐射模式,同时方向性增益得到增强.通过对其近场的观察和分析可以得知,新的辐射模式的产生来源于高阶模式的局域表面等离激元.结果表明,背景材料为GaN时,产生高阶模式局域表面等离激元的合适条件为电偶极子距银盘底部40nm.另外,为了有效地支持高阶模式局域表面等离激元的形成,银盘厚度与半径最小分别为30nm和100nm.本文的研究对掌握纳米银盘结构的光天线特性及其在光器件中的运用有重要意义.     

银纳米圆盘光天线的远场方向性研究

采用时域有限差分方法计算了银纳米圆盘光天线模型的场分布,研究了光偶极天线的远场辐射特性随距离和厚度、半径变化的规律以及影响其远场方向性的因素. 研究发现,偶极子垂直放置在银纳米圆盘下方一定距离时,银盘厚度和半径的改变均可使方向性图中出现新的辐射模式,同时方向性增益得到增强.通过对其近场的观察和分析可以得知,新的辐射模式的产生来源于高阶模式的局域表面等离激元. 结果表明,背景材料为GaN时,产生高阶模式局域表面等离激元的合适条件为电偶极子距银盘底部40 nm. 另外,为了有效地支持高阶模式局域表面等离激元的形成,银盘厚度与半径最小分别为30 nm和100 nm. 本文的研究对掌握纳米银盘结构的光天线特性及其在光器件中的运用有重要意义.     

量子等离激元光子学在若干方向的最新进展

等离激元光子学是围绕表面等离激元的原理和应用的学科,是纳米光学的重要组成部分.表面等离激元的本质是局域在材料界面纳米尺度内的多电子元激发.这一元激发可以与电磁场强烈耦合,使得我们可以通过纳米尺度结构接收,调控和辐射微米尺度光信息,并由此衍生出等离激元光子学的诸多应用.近年来,随着纳米加工尺度逼近量子极限,等离激元的量子特性受到了广泛关注.量子尺度的等离激元承接电子的波动性和光的粒子性,以其独特的內禀属性,在量子信息、高效光电器件、高灵敏探测等方面表现出十分诱人的前景.本综述重点介绍量子等离激元近年来的发展现状,回顾相关理论的发展以及与等离激元量子特性相关的一些突破性成果.最后对量子等离激元未来的发展进行了展望.     

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

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.     

表面等离激元增强的光和物质相互作用

表面等离激元近年来受到了广泛的关注.得益于表面等离激元的强局域约束作用,光场和能量被限制在亚波长尺度上,因而各种光和物质相互作用可得到显著的增强.表面等离激元的特性与材料、形貌、结构密切相关,相应的共振波长可覆盖紫外、可见光、近红外到远红外的光谱波段.由于表面等离激元的强局域电场,光与物质的相互作用,如荧光、拉曼散射、非线性光学、光热转换、光-声效应、催化、光伏转换等,都得以显著增强.本文简要回顾了表面等离激元的物理特性,具体讨论了各种基于表面等离激元增强的光和物质相互作用机理及相关应用,并探讨了存在的问题和进一步发展的方向.本文旨在为构造更高性能的表面等离激元器件,发展相关技术,进一步拓展表面等离激元的应用领域提供有益的参考.     

十字结构银纳米线的表面等离极化激元分束特性

金属纳米线波导可以将光局域在亚波长尺度内传播, 在纳米光子集成回路方面有着重要的作用. 本文应用有限元方法, 研究了十字结构银纳米线的表面等离极化激元分束特性. 结果表明, 不同模式的表面等离极化激元在十字结构三个分支的输出依赖于端面的几何结构参数. 此外, 研究还发现由于不同模式表面等离极化激元叠加, 在十字结构的分支上出现了周期性电场分布.     

人工表面等离激元超材料

以微带为代表的传统微波传输线无法精细操控电磁模式,因此传统电子信息系统在空间耦合、动态响应和性能鲁棒性等方面存在瓶颈。人工表面等离激元(SSPP)超材料可打破上述瓶颈,是光学与信息领域的研究热点之一。人工表面等离激元超材料是一类模拟光频段表面等离激元特性的新型超材料,可在微波和太赫兹频段精细操控表面波,具有与平面电路相似的构型特性,可用于制备下一代集成电路的基础传输线。人工表面等离激元分为传输型和局域型两类。传输型人工表面等离激元超材料始于三维立体结构,后发展成超薄梳状金属条带构型。学者们构建了以其为基础的微波电路新体系,研制了人工表面等离激元滤波器、天线、放大器和倍频器等典型的无源和有源器件,并将其集成为可实现亚波长间距多通道信号非视距传输的无线通信系统。人工局域表面等离激元(SLSP)超材料也经历了从三维立体构型到超薄构型的发展历程,并通过螺旋构型、链式构型、高阶模式和杂化模式等为电磁波的亚波长尺度调控提供了更多自由度。系统讨论了人工表面等离激元超材料在微波电路中的相关理论和应用,包括人工表面等离激元超材料的基本概念、构型发展、无源/有源器件以及无线通信系统。     

表面等离激元的聚焦与波导增强

近年来,表面等离激元学（plasmonics）已经形成一个新的学科热点.电子在金属与介质界面的集体振荡行为形成一种元激发——表面等离激元（surface plasomon polariton,SPP）.由于其具有特殊的耦合与传播性质,与SPP相关的器件设计与应用成为目前纳米光子学领域的国际前沿研究方向.文章介绍了利用微...     

Analysis of surface and guided wave plasmon polariton modes in insulator–metal–insulator planar plasmonic waveguides

Theoretical and experimental study of the surface plasmon–polariton and guided wave plasmon polariton modes is presented for the Sapphire/Ag/Polycarbonate/Air structure. Theoretical results are obtained by solving complex multilayer eigenvalue equations as well as the reflectivity equation for this structure. It is proposed that the mode attenuation can be significantly reduced by inserting a low index dielectric buffer between the metal and the guiding dielectric layer. The dispersion and attenuation curves are generated. Both the surface plasmon and guided wave plasmon polariton modes are studied experimentally. The experimental values of the effective refractive indices agree well with the theoretical values. The electric field profiles are generated and used to examine the nature of modes. After optimization of various parameters the condition for low loss single mode guiding is obtained for the proposed structure. Effect of metal thickness on surface plasmon mode is also discussed. It is inferred that in a properly optimized plasmonic waveguide, the losses can be reduced by a factor of 4.     

Dispersion and damping of a surface plasmon polariton on a one-dimensional randomly rough metal surface

Abstract

By the use of the reduced Rayleigh equation for the amplitude of a surface plasmon polariton on a one-dimensional randomly rough metal surface that is in contact with vacuum, we calculate the dispersion and damping of the surface electromagnetic wave to the lowest nonzero order in the rms height of the surface. It is found that the frequency of the surface plasmon polariton is depressed by the surface roughness. The attenuation of the surface plasmon polariton in the long wavelength limit is due primarily to its scattering into other surface plasmon polaritons, while in the short wavelength limit it is due primarily to its roughness-induced scattering into volume electromagnetic waves in the vacuum. The energy mean free path of the surface plasmon polariton is shorter on a randomly rough metal surface than it is on a lossy planar metal surface, and the surface plasmon polariton is more tightly bound to a rough surface than to a planar one.     

Extraordinary optical transmission through metal gratings with single and double grooved surfaces

We investigate the transmission properties of a normally incident TM plane wave through metal films with periodic parabolic-shaped grooves on single and double surfaces using the finite-difference-time-domain method. Nearly zero transmission efficiency is found at wavelengths corresponding to surface plasmon excitation on a flat surface in the case where the single surface is grooved. Meanwhile, resonant excitation of surface plasmon polariton (SPP) Bloch modes leads to a strong transmission peak at slightly larger wavelengths. When the grating is grooved on double surfaces, the transmission enhancement can be dramatically improved due to the resonant tunnelling between SPP Bloch modes.     

Calculated plasmonic enhancement of spontaneous emission from silicon nanocrystals with metallic gratings

The spontaneous emission rate (SER) enhancement due to the surface plasmon polariton (SPP) band gap effect of metallic gratings was evaluated by calculating the dispersion relation and electromagnetic field distribution simultaneously. Within the luminescence range of silicon nanocrystals (Si-NC) (?ω = 1.9 eV-1.6 eV), the calculated peak Purcell factors for Au-, Ag-, and Al-Si₃N₄ gratings are 266.9-30.1, 80.2-22.6, and 78.7-20.3, respectively. These results indicate that the common metals such as Au, Ag and Al, whose SPP resonance frequencies/energies are rather higher, can be adopted to enhance the SER of Si-NCs with the help of metallic gratings.     

Efficient directional excitation of surface plasmon polaritons by partial dielectric filling slit structure

In this paper, we investigate the excitation of surface plasmon polariton (SPP) in the metallic slit partly filled with dielectric by using the finite-difference time-domain method. It is found that the slit structure displays high asymmetry in the field distribution and SPP excitation due to the difference in matching degree of SPP wavevector on the two sides of slit exit. At certain incident wavelengths, the power flow carried by SPP modes on one side of slit exit is over three orders of magnitude greater than that on the other side, an efficient directional excitation is achieved. The SPP generation efficiencies on both sides of slit exit can be periodically adjusted by the dielectric width, but their changes are not synchronous, implying that such slit structure could be acted as a directional splitter/coupler. Moreover, the asymmetry degree of SPP excitation can also be modulated by the refractive index of dielectric layer.     

Beaming of light through depth-tuned plasmonic nanostructures

A nanostructure comprising dielectric/Ag interface with central slit surrounded by grooves is presented for beam focusing and collimating. Desired phase retardations of the beam emerging through slits are manipulated by tuning the depth of grooves. Numerical simulations are performed through a finite-difference time-domain (FDTD) algorithm. Results reveal the suitability of parabolic depth-tuned structure for enhanced transmission and beam collimation. Enhanced transmission and beam collimation are the result of transportation of electromagnetic energy in the form of surface plasmon polariton (SPP) waves.     

气体压强及表面等离激元影响表面波等离子体电离发展过程的粒子模拟

基于表面等离激元 (SPP) 的表面波等离子体 (SWP) 源, 具有高密度、低温度及高产率等优异性能, 其应用在电子器件微纳加工、材料改性等领域. 但由于SPP激励SWP放电的电离过程难于用理论分析和实验测量描述, 因而SWP源均匀稳定产生的电离发展过程一直未研究清晰. 本文以SWP放电的数值模拟为研究手段, 采用等离子体与电磁波相互作用的粒子模拟 (PIC) 方法, 结合蒙特卡罗碰撞 (MCC) 方法处理碰撞效应的优势, 研究气体压强影响电离过程的电磁能量耦合机理. 模拟结果表明SWP的高效产生是SPP的局域增强电场致使, 气体压强能够改变波模共振转换的出现时刻而影响了SWP的电离发展过程. 本文的研究成果展示了SPP维持SWP放电的电离过程, 可为下一代米级SWP源的参数优化提供设计建议. 关键词： 表面波等离子体 表面等离激元 粒子模拟 电离过程     

MIM结构的SPP模式理论与仿真计算研究

为了进一步明确MIM （Metal-insulator-metal）波导结构的SPP （Surface plasmon polariton）模式特性,建立了MIM结构的SPP模式关系、激发系数和反射系数的理论模型。仿真数值计算结果表明：较大的介质厚度的TM基态模式衰减超过了振荡模式衰减,与传统的介质波导明显不同;TE模式表现为失真的介质光波导模式特性,其传播距离要远大于TM₀;MIM结构中腔的Q值随着长度增加而增大,表明了SPP反射受限;腔的品质因数改变与端面关系密切;MIM波导可以在具有更大Q值下确保光波更好地耦合成需要的SPP模式。     

Surface-plasmon-assisted electromagnetic field enhancement in semiconductor quantum dots

The temporal development of incident electromagnetic plane waves across semiconductor quantum dots (QDs) is analyzed by the finite-difference time-domain method. By coating the QDs using thin metal films, surface plasmon polaritons (SPPs) can be created. As illustration, our modeling approach is applied to fluorescent multiphoton quantum dots made of cadmium sulphide of particular size (3.7 nm) and energy band gap (2.67 eV). When such a QD is coated by a metal film, a dipole-formed SPP is generated at the external surface of the coated QD by the incident electromagnetic wave with a photon energy of 1.34 eV corresponding to a two-photon process. When the thickness of the metal film is 0.37 nm, the peak intensity of the SPP oscillates through both the thin metal film and the core QD, resulting in an electromagnetic field inside the QD enhanced by a factor of 10, and thus an increased two-photon excitation that can be useful for bioimaging applications. Further increasing the metal film thickness blockades the SPP initially generated at the external surface of the coated QD from penetrating through the metal film, reducing the electromagnetic field inside the QD. PACS 73.22.-f; 78.67.Hc