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     

金纳米环双体尺寸和耦合效应对表面等离子体共振特性的影响

采用离散偶极子近似方法系统地研究了金纳米环双体的消光光谱及其电场分布. 计算结果表明, 金纳米环双体在耦合作用下的共振消光峰对应着不同振动模式, 改变金纳米环双体的排列方式、 间距和尺寸大小, 其表面等离子体共振消光峰发生红移或蓝移. 因此可以通过对金纳米环双体结构参数和排列方式的设定, 调节其表面等离子体共振消光峰的位置. 电场分布表明, 水平排列的金纳米环双体较单个金纳米环产生更强的局部表面增强电场. 适当的小间距, 较大的内外半径的金纳米环水平阵列更适合做表面增强拉曼散射的衬底, 在生物分子检测等领域具有潜在的应用.     

Enhanced optical transmission through an array of compound unit with multiple concentric or eccentric annular apertures

In this paper, transmission properties through an array of compound unit with multiple concentric or eccentric annular apertures are numerically studied. It is demonstrated that the transmission of the compound structure is not a simple superposition of that of each annular aperture array but exhibit substantial changes in both the position and intensity of resonant peaks. It is also found that the gap plasmon resonance exhibit split peaks when the symmetry is broken, which can be well explained from the view of charge oscillation. These properties provide a method to achieve enhanced transmission in multi-frequencies simultaneously and are of significant applicable value to the design of tunable optical devices.     

Broadband efficient light absorbing in the visible regime by a metananoring array

The broadband efficient light‐absorbing property of a metamaterial‐based subwavelength nanoring array in visible regime is reported. The nanoring array can absorb light efficiently with an average absorptivity of 0.97 over the whole visible waveband. In addition, it is found that this kind of super light‐absorbing capability is independent of the incoming light polarization state and can maintain an average of 0.9 for an incident angle as large as ±60° under TM illumination. The perfect absorbing property of the metamaterial‐based nanoring array is attributed to the synergetic effect of the Fabry–Perot resonance and the localized surface plasmon resonance enhancement.     

Versatile nanosphere lithography technique combining multiple-exposure nanosphere lens lithography and nanosphere template lithography

A versatile nanosphere composite lithography(NSCL) combining both the advantages of multiple-exposure nanosphere lens lithography(MENSLL) and nanosphere template lithography(NSTL) is demonstrated. By well controlling the development, washing and the drying processes, the nanosphere monolayer can be well retained on the substrate after developing and washing. Thus the NSTL can be performed based on MENSLL to fabricate nanoring, nanocrescent and hierarchical multiple structures. The pattern size and the shape can be systemically tuned by shrinking nanospheres by using dry etching and adjusting the tilted angle. It is a natural nanopattern alignment process and possesses a great potential in the scope of nano-science due to its low cost,simplicity, and versatility for variuos nano-fabrications.     

Light scattering study of surface plasmon resonances in very thin silver films

The surface plasmon modes of Ag thin films were studied by the light scattering method in the thickness range down to 100 Å. The observed thickness dependence of the resonance peaks was analysed in detail by the theory of Kretschmann. It is shown that the coupled surface plasmon modes in the very thin films can be detected only in modified forms by the light scattering experiment.     

Tunable phaselike resonance in split coaxial gold nanotube resonator pair

We propose the split coaxial nanotube resonator pair and investigate its plasmon resonance properties theoretically. It is found that the resonance peak splits and forms more dips with the increase of the number of slits in the structure. We present that the splitting behaviors result from the phaselike resonance of adjacent tubes. In addition, it shows the optical transmission peaks can shift and attenuate by tuning the split width, the thickness and dielectric constant of the medium layer between two coaxial nanotubes. The instantaneous electric field distributions show that symmetry and antisymmetry quadrupole modes exist in these structures.     

基于法布里-珀罗腔的纳米环滤光器

同轴纳米环结构由于具有特殊的光学特性, 近年来引起了科学界的广泛关注. 本文将重点研究在以纳米环形结构为基础的法布里-珀罗腔中所存 在的两种形式的表面等离子共振, 平面型和传输型. 通过使用固定圆环阵列的周期而只改变圆环孔径大小的方法来实现调 节传输型共振并达到滤波的效果. 同时, 控制圆环阵列的周期使其足够大, 从而使得平面型共振峰位于近红外波段, 以避免对处于可见光波段的传输型共振模式形成干扰, 最终实现滤光效果. 在实验中, 通过使用周期固定为1200 nm而孔径大小从10到180 nm (以10 nm递增)的同轴圆环结构, 实现了把一束宽带的白光源分成不同颜色的单色光. 实验结果表明, 该方法解决了天线凹槽和一维层堆光栅型滤光器都普遍存在的偏振敏感性问题, 使得类似滤光器件的应用范围更广, 更能适应非偏振的自然光. 通过有限时域差分法分析得到的理论计算结果和实验结果相匹配, 实验现象得到了很好的理论支持和解释. 关键词： 表面等离子体 同轴圆环纳米腔 透射型滤光器     

周期地嵌入电介质球壳的金属表层的表面等离子激元及其与电介质腔体模式的耦合

通过观察金属底板中周期地嵌入电介质球壳的体系的光学吸收性质，研究了表面等离子激元 以及与其他电磁模式的耦合特性.在这种周期结构的金属表面，发现存在两种响应频率，分 别对应于表面等离子激元模式和金属中的电介质腔体模式.在这些响应频率上，可观察到与 它们相对应的吸收峰.由于金属的表面模式不能与平面入射光直接耦合，而腔体模式与平面 入射光和表面等离子激元模式的耦合一般较弱，因而通常情况下这些吸收峰的峰值有限.然 而，通过调整体系中的某些参数，可以使腔体模式和表面模式的频率非常接近，这时二者之 间的耦合强度将大大提高.此时，在相应的频率附近可观察到极强的吸收峰.详细地研究了介 质球壳的物理和几何参数对此共振吸收的影响. 关键词： 腔体模式 表面等离子体模式 共振吸收     

三角形钠原子团簇中的表面等离激元

运用含时密度泛函理论研究等边三角形钠原子团簇中的表面等离激元激发.发现:在团簇尺寸较大时,沿三角形底边和底边中垂线方向激发的共振模式不同,然而沿两方向的吸收光谱线形一样,主要吸收峰的共振能量也相同.低能聚集共振在空间引起电场增强的极大值主要分布在三角形的端点附近.     

Effect of Aspect Ratio Distribution on Localized Surface Plasmon Resonance Extinction Spectrum of Gold Nanorods

Gold nanorods with different aspect ratios are prepared in micells using a seeded growth method. Their extinction spectra are observed with an UV-visible spectrophotometer and analysed theoretically. It is known that there are two plasmon resonance peaks for gold nanorod corresponding to transverse and longitudinal plasmon resonance respectively. Moreover, the longitudinal plasmon resonance peak shifts to long wavelength when we increase the aspect ratio determined from TEM. Especially, we model the extinction spectrum using Gans' theory and compare it with our experimental result. Considering the aspect radios distribution of gold nanorods, it is found that longitudinal plasmon resonance peak will be wider than the nanorods with single aspect ratio, which is consistent with our experimental result. In addition, the effect of dielectric constant of surrounding medium is considered.     

Transmission properties of periodically patterned triangular prisms

Transmission properties of plasmonic structure arrays are simulated by finite element method. The array unit is composed of two combined triangular prisms. Results reveal that several resonant modes are found in the transmission spectra, which are due to the resonance of the surface plasmon polariton in the metal slit or to the localized surface plasmon resonance of the combined prisms. The resonant wavelengths can be tuned by changing the structural parameters of the combined prisms. In addition, the resonant modes are sensitive to small refractive index changes of the surrounding media, revealing potential detection applications in nanophotonic systems.     

Light transmission properties of double-overlapped annular apertures

We investigate the light transmission properties of double-overlapped annular apertures in a silver film with the three-dimensional finite-difference time-domain method. It has been found that the transmission peaks are attributed to the localized surface plasmon resonance (LSPR) of nanocavities and the surface plasmon polaritons (SPPs) of the nanoparticles. The peaks of the LSPR are blueshifted when the overlapping distance is increased. Moreover, a Fano-type resonance appears in the transmitted spectral response with an appropriate overlapping distance, which is elucidated as the hybridization results of the SPPs of the nanoparticles. The number and position of the Fano resonance can be tuned through varying the overlapping distance and other geometric parameters.     

光子角动量在环形金属纳米孔异常透射过程中的作用

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.     

Mid-infrared optical resonances in quantum dot photodetectors coupled with metallic gratings with different aperture diameters

The paper is devoted to optical testing of mid-infrared Ge/Si photodetectors obtained by stacking of self-assembled Ge quantum dots in multilayer structures, which are near-field coupled to the adjacent nanoplasmonic arrays of subwavelength holes in metallic films. It is shown that photocurrent and near-field spectra consist of several sets of peaks, which are attributted to surface plasmon waves, localized surface plasmon modes or diffractive Rayleigh anomaly depending on the hole diameter and the angle of incidence θ. We find that for small holes the greatest contribution to the photocurrent enhancement is due to the excitation of the surface plasmon-polariton waves for all θ. As the hole diameter is increased and becomes comparable with the array periodicity, the normal-incident photoresponse improvement is provided by the Rayleigh anomaly. With the increase of incident angle, the photocurrent enhancement is supposed to arise from coupling of the localized shape resonance and propagating plasmon modes.     

Polarization detection analysis of dual-channel surface plasmon resonance sensing for silicone oils based on the D-shaped fiber with a central hole

We present and numerically characterize a dual channel surface plasmon resonance (SPR) sensor based on a D-shaped fiber with a central hole for silicone oil detections. The proposed design incorporates two metalized channels to facilitate the simultaneous detection of one group of silicone oils, which can consist of two different species. It has been demonstrated that the p-polarized input light can induce two peaks among surface plasmon resonance places, which come from the coupling between the core-guided mode and the fundamental surface plasmon polariton (SPP) modes at the D-shaped surface and around the central hole surface. However, the s-polarized input light can only induce one peak among surface plasmon resonance places, which comes from the coupling between the core-guided mode and the fundamental SPP mode around the central hole surface. The simulation results show that the characteristic responses of two channels independently correspond to the refractive index variations in the silicone oils with which they are in contact. A maximum sensitivity of 3500 nm/RIU (refractive index unit) and 4400 nm/RIU are achieved for channel A and B, respectively. This kind of sensor structure and polarization related demodulation method is promising in the simultaneous multi-analytes sensing applications in the future.     

A novel plasmonic refractive index sensor based on gold/silicon complementary grating structure

A novel complementary grating structure is proposed for plasmonic refractive index sensing due to its strong resonance at near-infrared wavelength.The reflection spectra and the electric field distributions are obtained via the finite-difference time-domain method.Numerical simulation results show that multiple surface plasmon resonance modes can be excited in this novel structure.Subsequently,one of the resonance modes shows appreciable potential in refractive index sensing due to its wide range of action with the environment of the analyte.After optimizing the grating geometric variables of the structure,the designed structure shows the stable sensing performance with a high refractive index sensitivity of 1642 nm per refractive index unit(nm/RIU)and the figure of merit of 409 RIU^-1.The promising simulation results indicate that such a sensor has a broad application prospect in biochemistry.     

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.     

Band structure of two-dimensional square lattice photonic crystals of circular dispersive metamaterial rods

By virtue of the efficiency of the Dirichlet-to-Neumann map method, the details of the band structure of a two-dimensional square lattice photonic crystal composed of dispersive metamaterial circular rods in air background has been studied. We show that there are two flat bands at the band structure of the system for both H-polarization and E-polarization. These flat bands are created around the magnetic resonance frequency, surface plasmon frequency and magnetic surface plasmon frequency. We realized that the modes with frequencies lying above the resonance frequency behave like resonant cavity modes created in a single metallic cylindrical waveguide. While, due to the relatively large and imaginary refractive index of the metamaterial rods at the frequencies lying below the resonance frequency, the modes are localized modes with negligible penetration into the rods. Moreover, the modes are localized at the interface of the cylindrical metamaterial rods and the air background for the frequencies around the surface plasmon frequency and the magnetic surface plasmon frequency.     

Transmission of light through coaxial and non-coaxial double-layer gold slit arrays

We investigate numerically the transmittance of light through gold double-layer structures with periodic coaxial and non-coaxial slits. We attribute the enhanced optical transmission to the surface plasmon resonance collaborating with the localized waveguide resonance. The transmission spectra and the surface electric fields are used to characterize the resonances of both types. For the coaxial system, with the increase of the slit width of the second layer, the resonance peak values of both types increase sharply at first until the two layers have the same slit width and then decrease dramatically; additionally, the center of the localized waveguide resonance peak shifts to shorter wavelength noticeably, but the surface plasmon peak center moves negligibly. As regards the non-coaxial structure, it shows a similar behavior of the localized waveguide resonance peak to that of the coaxial one; however, the surface plasmon resonance peak behaves in a different way. These results may be associated with the surface plasmon coupling modes and the Fabry–Perot cavity modes in the double-layer structure.