Ag-Al纳米球二聚体的光学性质研究

金属纳米材料因其表面等离子体共振特性而备受关注。异质结构的金属纳米材料的光学特性相比于同质结构因其材料的不同破坏了原有结构的对称性,对称性的破坏将引起光学性质的改变,相邻两个颗粒之间的相互作用会产生Fano共振。Fano共振是由异质纳米结构的表面等离子体共振耦合引起的,通过合理地调控表面等离子体共振的耦合,将进一步调控Fano共振的强度同时促使异质结构的电场增强特性和辐射特性得到进一步优化。受金银等贵金属的带间跃迁影响,金属铝纳米材料成为研究紫外-近紫外光区的表面等离子体共振研究最佳选择。采用有限时域差分方法研究了Ag-Al纳米球二聚体的光学特性。研究了Ag和Al纳米球组成的二聚体的吸收光谱与入射光偏振方向、纳米球半径、颗粒间距和介质折射率等几何结构及物理参数的关系,并深入讨论了二聚体的局域场分布规律;讨论了获取更高效的Fano共振光谱的方法。由于材料的对称性被破坏,异质二聚体的光学性质与同质二聚体明显不同,Ag-Al异质纳米球二聚体呈现出在紫外和可见光区的双Fano共振现象。Ag-Al二聚体表面等离子体互相耦合引起Fano共振从而导致表面等离子体的共振抑制和增强。研究结果对在紫外-可见光区的表面等离子体应用、纳米光学器件的设计与开发及基于表面等离子体共振的表面增强光谱、生物传感和检测研究等有一定参考价值。     

银纳米棒双体结构的表面等离子体共振光学特性研究

利用时域有限差分方法,研究了银纳米棒双体结构的散射光谱及其电场分布,并对其局域表面等离子体耦合共振特性进行了分析。研究表明随着银纳米棒之间的距离变大,其表面等离子共振峰的强度逐渐变弱,横向四极模式和横向偶极模式峰位基本不变。纳米棒半径的增加和夹角的变大,都会引起峰值强度明显增强。通过场分布计算发现,纳米棒半径的增加和夹角的变大都可以在颗粒的近场区域产生"热点",这种局域电磁场显著的增强对表面增强拉曼散射、荧光探针、纳米催化等方面的应用具有参考价值。     

纳米光子学的最新进展

论述了纳米光子学的最新进展，介绍了国际上的一些研究小组所做的关于纳米光子学的实验，包括纳米开关、近场光学探针技术、近场光化学气相沉积制备、基于等离子体激元波导实现的远近场能量的转换装置等内容，着重阐明实验原理和纳米制备技术中的一些关键问题。     

金纳米环结构的光学性质研究

采用离散偶极子近似方法(DDA)研究了两种不同形状的金纳米环结构的消光光谱及其近电场分布, 研究了等离子体消光峰的红移、蓝移现象及消光系数与结构参数之间的关系, 并与盘状的金纳米结构进行了比较. 在等离子体共振峰波长入射时, 金纳米环结构比金纳米盘结构产生更大的局域增强电场分布, 横截面为圆形的金纳米环结构比横截面为矩形的结构具有更大的局域增强电场分布, 更适合作为表面增强拉曼散射的衬底. 关键词： 离散偶极子近似 金纳米环 金纳米盘 光学性质     

银纳米粒子阵列中衍射诱导高品质因子的四偶极晶格等离子体模式

金属纳米颗粒阵列中形成的四偶极晶格共振模式具有低辐射损耗、高品质因子的特性,因此广泛应用于纳米激光、传感、固态照明等领域.基于时域有限差分法在均匀环境下研究了银纳米圆柱阵列的光谱与近场特性.研究结果表明,在x偏振光直入射下,通过调节阵列x方向的周期,共振强度先增加后降低,当两个方向上的周期相等时,提出的阵列结构能够产生一个线宽约0.4 nm、品质因子高达1815的四偶极晶格共振模式,这种共振模式呈现出Fano线型的透射谷;调控y方向的周期能够实现从Fano线型的透射峰到透射谷的转变.本文说明了粒子大小、晶格周期对四偶极晶格共振模式的重要性,同时为银纳米颗粒在可见光波段设计高品质因子共振提供了优化策略.     

不同密度银纳米粒子对氧化锌基发光二极管发光的增强

采用分子束外延法制备不同密度的银纳米粒子(AgNPs)修饰的局域表面等离子体共振增强n-ZnO/iZnO/MgO/p-GaN异质结发光二极管(LEDs),并对其电学及光学性质进行表征。结果显示:LEDs中引入适当浓度的AgNPs有利于AgNPs局域表面等离子体激元与ZnO激子相耦合,可以显著提高器件的电致发光性能;随着AgNPs浓度的增加,LEDs发光增强倍数先增大后减小,分析认为这是AgNPs局域表面等离子体共振耦合增强过程和AgNPs的消光过程两者之间相互博弈而导致的结果。     

金局域表面等离激元增强砷化镓发光特性

研究了金纳米颗粒局域表面等离激元共振耦合效应,并实现了砷化镓薄膜的近场发光增强.通过理论计算金纳米颗粒的吸收光谱及电场分布,分析金属纳米颗粒形貌尺寸的改变对等离激元共振频率调控及局域场增强效果的影响,模拟半径为50nm的金颗粒并实现了35倍近场增强效果.通过对双球型的模拟,分析了一种金纳米颗粒增强GaAs的积极方式,即密集颗粒之间的近场耦合形成的"hotspots".此外,研究了不同溅射时间及快速退火对金纳米颗粒吸收特性的影响,发现金纳米颗粒吸收峰位主要位于560～680nm波段,而且随着溅射时间的增加发生红移现象.经过快速退火处理后,金纳米颗粒吸收峰位蓝移到510～550nm波段,形成与532nm激发波长相匹配的共振吸收峰.最后,实现砷化镓薄膜9.6倍的光致发光增强.     

带有T型腔的MIM波导的法诺共振特性研究

设计了一种带有枝节的金属-介质-金属(MIM)波导与T型谐振腔侧耦合的表面等离子体光波导结构。利用有限元法(FEM),数值分析了改变耦合距离、T型腔几何尺寸及其不对称性、枝节高度对法诺(Fano)共振谱线的影响。结合电磁场分布进一步揭示了Fano共振现象产生的物理机理,由此可以动态调节表面等离子体波在结构中传输时产生的Fano共振特性。另外,研究表明在T型腔内填充不同折射率的材料,利用所设计的波导结构可以实现灵敏度高达940nm/RIU的纳米尺度的折射率传感器。最后研究了结构的慢光传输特性,可以在Fano峰值附近实现约0.025ps的光学延迟。这种新型的表面等离子体光波导可能会在光子器件集成、慢光效应及纳米传感领域有着较大的应用前景。     

基于金属表面等离子激元控制光束的新进展

表面等离子激元(Surface plasmon polaritons,SPPs)是一种在金属-介质界面上激发并耦合电荷密度起伏的电磁振荡,具有近场增强、表面受限、短波长等特性,在纳米光子学的研究中扮演着重要角色。近年来表面等离子光学和基于SPPs的纳米光子器件的研究引起了国际上科学家们的广泛关注。讨论了SPPs的基本原理和在亚波长结构下的光学特性,介绍了基于亚波长金属结构的表面等离子激元在空间光束准直与聚焦、平面内光束聚焦与传导和在近场纳米光束的控制等方面的研究情况,以及在纳米光子学器件中的潜在应用。     

基于纳米光学等离子晶体的新型纳米光子学器件的发展

通过设计合适的纳米表面等离子结构,纳米光学等离子晶体具有光场增强效应,能调控近场范围内的光场分布,可用来设计新型的纳米光子学器件。介绍了纳米光学等离子晶体的原理、结构特点、制作工艺和纳米光子学器件的设计方法,对纳米光学等离子晶体和普通光子晶体做了比较。归纳了纳米光学等离子晶体的物理机制、光学特征,描述并分析了波长选择性场增强效应和束流效应等。给出几种基于纳米光学等离子晶体的纳米光子学器件应用实例。     

Fano profile in a novel double cavity optomechanical system with harmonically bound mirrors

We investigate a double cavity optomechanical system generating single and double Fano resonance (multi-Fano). By altering a single parameter, the tunnelling rate g of the middle mirror, we are able to switch between single and double Fano line shapes. The first spectral line shape is stronger in the case of multi-Fano than in the case of single Fano. Also the behaviour of the steady state value of the displacement of the middle mirror, with respect to g, heavily influences the behaviour of double Fano lines in our scheme. This tunability along with using a single pump and signal/probe laser has an added advantage in situations where only low power consumption is available.     

同心椭圆柱-纳米管结构的双重Fano共振研究

提出了一种同心椭圆柱-纳米管复合结构,该结构由金纳米管中内嵌椭圆形金柱构成,利用时域有限差分法分析了尺寸参数、周围环境及纳米管内核材料对该结构光学性质的影响.结果表明,调节椭圆柱芯的旋转角度可产生双重偶极-偶极Fano共振,其主要是由椭圆柱芯的纵向或横向偶极共振模式与纳米管的偶极成键和反成键模式杂化形成的超辐射成键模式和亚辐射成键模式之间的相互作用产生的,且共振特性可通过调节复合结构的尺寸参数控制,随椭圆柱长轴或短轴的增大而红移,随纳米管外径的增大或整体尺寸的减小而蓝移,当纳米管内径增大时高频Fano共振随着红移,而低频Fano共振先蓝移再红移,同时其对外界环境的变化不敏感,但对纳米管内核材料变化有着较好的响应.利用等离激元杂化理论对该现象进行了解释.这些结果可为构造其他类型的多波段Fano共振二维或三维纳米结构提供一种新的方式.     

Refractive Plasmonic Sensor Based on Fano Resonances in an Optical System

A symmetric plasmonic structure consisting of metal-insulator-metal waveguide, groove and slot cavities is studied, which supports double Fano resonances deriving from two different mechanisms. One of the Fano resonances originates from the interference between the resonances of groove and slot cavities, and the other comes from the interference between slot cavities. The spectral line shapes and the peaks of the double Fano resonances can be modulated by changing the length of the slot cavities and the height of the groove. Furthermore,the wavelength of the resonance peak has a linear relationship with the length of the slot cavities. The proposed plasmonic nanosensor possesses a sensitivity of 800 nm/RIU and a figure of merit of 3150, which may have important applications in switches, sensors, and nonlinear devices.     

Wideband slow light achievement in MIM plasmonic waveguide by controlling Fano resonance

In this paper, we have investigated the characteristics of an asymmetric shaped Fano line in a metal–insulator–metal (MIM) plasmonic waveguide side coupled to two resonating stub structures. The spectral properties of Fano resonance are quite distinct due to the destructive interference between a two propagating plasmon modes. Two structural parameters are carefully adjusted: physical separation between both the resonating stubs and length of resonating stubs. By tailoring the separation between both the resonating structures, coupling between both the plasmon modes is controlled, and hence asymmetric nature of Fano line can be shaped accordingly. Resonance condition of Fano line can be tuned by scaling the length of stubs. A strong red shift in resonating wavelength with varying degree of asymmetry is observed, when length of resonating structures is increased. The sharp resonant peak, due to an asymmetric shaped Fano resonance is generally accompanied by large dispersion that results in reduction of group velocity of light near Fano resonance. By controlling the coupling between resonating stub, or by scaling the length of lower resonating stub, large value of group index (n_g = 75) and delay bandwidth product (DBP = 0.2533) is obtained. The structure can be modified to suit different applications in optical buffers, optical switches and nonlinear optics devices.     

X-两环结构的光学特性研究

提出了一种X-两环的金属周期性阵列结构,该结构由两个同心圆环包围中心X型构成.利用时域有限差分算法研究了该结构的光学特性.计算表明,当光入射到金属表面时,能够在结构中产生法诺共振现象,并在不同的位置下产生共振谷.同时,共振谷的出现又明显依赖于结构的相对参数(X的臂长、内外环的距离、内外环宽度、周期、环数、X所呈的角度),从而可以通过调节结构的相对参数来实现对结构的共振强度及共振谷位置的调控.另外,进一步分析了在不同环境折射率条件下该结构共振谷的变化规律,可以得出该结构也对周围的环境折射率有着较高的敏感度,最高可达1300 nm/RIU.结果表明,该结构在环境折射率传感器及某些光子器件的应用方面有着潜在的价值.     

ac field-induced Fano resonances in a parallel-coupled double quantum dot system

The effects of an ac electric field on the Fano resonance in a parallel-coupled double quantum dot system are investigated theoretically. The field can induce the photon-assisted Fano resonances for both symmetrical and asymmetrical parallel configurations. The magnitude and position of the photon-assisted Fano peak can be tuned by the ac field strength and frequency, respectively. Furthermore, the Fano resonance can appear with increasing the field frequency for both the symmetrical and asymmetrical configurations. This provides an efficient mechanism to control the Fano resonance. The photon-electron pumping effects for the symmetrical and asymmetrical cases are also studied in the weak- and strong-coupling regime.     

基于硅基光子器件的Fano共振研究进展

硅基光子技术的发展为新型微纳光学功能器件和片上系统提供了高可靠、高精度的实现手段.采用硅基光子技术构建的具有连续(准连续)模式微腔与离散模式的微腔耦合产生的Fano共振现象得到了广泛关注.Fano共振光谱在共振波长附近具有不对称且尖锐的谐振峰,传输光的强度在共振波长附近从0突变为1,该机制可显著提高硅基光开关、探测器、传感器,以及光非互易性全光信号处理的性能.本综述分析了Fano共振的一般数学表述,总结了当前硅基光子微腔耦合产生Fano共振的理论模型研究现状,讨论了不同类型硅光器件实现Fano共振的方法,比较各种方案优劣及适用场合,梳理了Fano共振在全光信号处理方面的应用研究情况.最后探讨存在的一些问题及未来可能的相关研究方向.     

Spin-flip induction of Fano resonance upon electron tunneling through atomic-scale spin structures

The inclusion of inelastic spin-dependent electron scatterings by the potential profiles of a single magnetic impurity and a spin dimer is shown to induce resonance features due to the Fano effect in the transport characteristics of such atomic-scale spin structures. The spin-flip processes leading to a configuration interaction of the system’s states play a fundamental role for the realization of Fano resonance and antiresonance. It has been established that applying an external magnetic field and a gate electric field allows the conductive properties of spin structures to be changed radically through the Fano resonance mechanism.     

Modification of the resonance fluorescence spectrum of a two-level atom in the near field of a plasmonic nanoparticle

The resonance fluorescence spectrum of an atom located in the near field of a plasmonic nanoparticle is considered. It is shown that, as the atom gets close to the nanoparticle, the high-frequency peak of the Mollow triplet disappears and the spectrum has a Fano resonance shape. The low-frequency peak also disappears as the distance between the atom and the nanoparticle decreases further. For small distances, when the atom interacts with the nanoparticle much more strongly than with the external field, the spectrum represents a Lorentzian line whose width is proportional to the square of the atom-nanoparticle coupling constant.     

Shape of Fano resonance line spectra calculated for silver nanorods

Using theoretical tools, we numerically demonstrated Fano line shapes in the scattering spectra of silver rods resulting from different mechanisms. One of the Fano line shapes is due to the coupling of an in-plane quadrupole and a dipole mode in a single rod. Two nodes were observed at the resonance wavelength, each of which is located at a quarter of the rod length from the two ends. The Fano resonance is strengthened when the silver rod is cut at the two nodal positions. The second mechanism that gives rise to a new Fano resonance peak occurs when the symmetry of the rod is broken and is a result of the asymmetric coupling between the two excited dipoles.