利用二维光放大图像的显微镜

生物学家一直梦想着有一台高精度的摄像机能拍摄下小于光波波长的活细胞的图像．最近美国马里兰大学的Igor Smolyaninov教授领导的研究组显示了这方面的成果．科学家们以前就知道，当光照射在一块金属表面时，它可以激发出一种波，称为表面等离体子(plasmon)，它实际上是一种二维电磁波与导电电子耦合的光波，有时就称为二维光波．     

用扫描近场光学显微镜技术研究金膜表面等离体子共振

表面等离体子波(SPW)可与入射光横磁波极化能量耦合并被共振激发,这种现象被称为表面等离体子共振现象(SPR)。主要利用扫描近场光学显微镜(SNOM)技术和表面等离体子共振现象技术相结合,来研究金膜表面等离体子共振。设计并建立了结构独特的新型Kretschmann型表面等离体子共振现象耦合装置,同时又设计了具有厚度梯度的表面等离体子的制备方法。在此基础上,测量了改变入射角条件下的表面等离体子共振曲线,测得该装置的等离体子共振角灵敏度为1°。并且对金膜表面进行表面等离体子共振条件下的扫描近场光学显微成像。实验结果表明,在共振时金膜表面的扫描成像比不共振时清晰,而且增加了很多细节。应用表面等离体子共振现象技术将可以明显提高扫描近场光学显微镜的信噪比、分辨力等性能。     

KT—5B托卡马克上离子伯恩斯坦波的传播特性

一、引 言 在一些较大型的托卡马克装置上的研究业已表明,应用外激发离子伯恩斯坦波(IBW)对托卡马克等离子体进行辅助加热是一种极具有竞争力的方法。然而,对在托卡马克位形的等离于体中,IBW的激发、传播等一些基本过程,仍需做进一步的实验研究。我们利用小型装置的低温、低密度特点,采用高空间分辨的射频(RF)电探针作为IBW的主要探测     

介质填充型二次柱面等离激元透镜的亚波长聚焦

本文提出了一种亚波长聚焦的表面等离激元透镜,该透镜由二氧化硅填充金膜纳米狭缝阵列组成,金膜的出射表面为二次柱面.表面等离激元在狭缝入口处激发并沿狭缝传输,在狭缝出口转变为带有一定相位延迟的自由空间传播的光波.通过对透镜结构参数的控制,可以调节来自各狭缝的光波间的相对相位,使它们在设定的焦点处进行相长干涉,从而实现聚焦效果.本文用时域有限差分法数值计算了二次柱面等离激元透镜的聚焦特性.数值模拟结果表明,所设计的孔径为2μm的透镜,能够实现微米级焦距和焦深、且焦斑半高宽低至0.4倍波长的亚波长聚焦.该表面等离激元透镜结构简单紧凑、尺寸小,有利于光子器件的集成,在集成光学、光学微操纵、超分辩率成像、光存储、生化传感等相关领域有潜在的应用价值.     

多通道体全息子波相关器及其在指纹识别中的应用

基于子波匹配相关理论经和光折变晶体的本全息关联存储特性,有用球面波作参考光,构建了一个新型的多通道体全息子波相关器。该系统具有多通道并行相关特性和更高的识别准确率,并且较通常的平面参考光波体全息相关器更为紧凑,易于小型化和实用化。初步研究了其在指纹识别中的应用,给出了实验结果。     

基于杂化表面等离激元的多层波导布拉格光栅

根据杂化表面等离激元的产生机理和传统杂化表面等离激元的波导结构,提出了一种多层波导布拉格光栅结构。该结构采用SiO2和NaF两种低折射率介质作为芯层,形成了多层波导布拉格光栅的结构。在1550nm通信波长下,围绕光波的传输距离和模场限制能力对光栅的结构进行了研究及优化。在此基础上,进一步分析了光栅周期数与光波反射率之间的关系。仿真结果表明:该光栅的传输距离和有效模场面积分别为178.12μm和0.203μm2;该结构不仅可以降低金属表面对光场限制所形成的损耗,而且表现出了较强的模场限制能力;当周期数为60时,光波的反射率能够达到71.9%,该结构具有良好的滤波特性。     

纳米银线波导中表面等离极化波激发和辐射的偏振特性研究术

在可见光波段（λ=750nm）,实验研究了在端面辅助情况下,细纳米银线波导中表面等离极化波激发和辐射的偏振特性．实验发现在细纳米银线中,不同偏振态的入射光对应的表面等离极化激元的激发和传输效率有明显不同,但对应的出射光始终为方向恒定的线偏振光．对于化学合成的纳米银线,端面的轴对称性普遍比较好,对此类纳米银线进行激发时,如果入射光偏振态与纳米线近似平行,则激发和传输表面等离极化激元的效率最高;如果正交,激发和传输效率则最低．对于某些端面轴对称性较差的纳米银线,如端面为尖端或类斜面,当入射光偏振态与纳米线有一定夹角时,激发和传输表面等离极化激元的效率最高．在入射光偏振改变的过程中出射光的偏振方向始终与纳米银线平行．最后结合有限元差分方法理论解释了纳米银线中这种偏振特性的物理机理．利用纳米银线中表面等离极化激元激发和辐射的偏振特性,可以在亚波长尺寸上实现对光强和偏振态的调控．     

稳态装置中的尘埃等离子体状态

介绍了用于研究尘埃等离子体中波的直流放电的尘埃等离子体装置,该装置能产生长约３０ｃｍ,直径约８．４ｃｍ的尘埃等离子体柱。在等离了体中加入尘埃后,朗缪尔探针的饱和电流明显降低。尘埃所带负电量与电机转速成正比,可达到等离子体负电量的４０％。     

离体射流的位置对翼型气动特性的影响

为了改善风力机叶片流动分离现象,本文在雷诺数为1×106、来流攻角21°时研究了离体射流微小圆柱的分布位置对NACA0018翼型气动性能的影响.首先分别在翼型前缘前和上表面附近,研究离体射流微小圆柱的射流动量对翼型气动性能的影响,发现两种位置下翼型的气动性能都有所改善,其中上表面附近控制时效果更好;接着研究控制装置在上...     

二维随机介质中偏振模式的竞争和阈值特性

基于随机激光的时域理论,建立了横磁与横电光波模式共享反转粒子数情况下的理论模型,并利用时域有限差分法(FDTD)数值求解麦克斯韦方程组和速率方程组,从而获得了二维随机介质内横磁与横电光波模式的阈值特性.结果表明,如果横磁与横电偏振模式之间没有共享反转粒子数,则横磁光波模式拥有较低的激发阈值;反之,则横电光波模式的激发阈值更低.在共享反转粒子数的情况下,改变样品的表面填充率对两种偏振模式的阈值并没有很大的影响,而增加样品面积则可以明显的降低横磁模式的阈值.     

Plasma resonance radiation from non radiative plasmons

Non radiative surface plasmons decay into photons on a rough surface. This light emission is studied with gold- and silver foils of different thicknesses. The surface plasmons are excited in this experiment by light. By this way a relatively accurate determination of the optical constants is possible.     

Polarization controlled couplings of surface plasmon with asymmetrical nanoslit pairs

Light-driven surface plasmons offer an opportunity to ultrafast information processing combining the compactness of electric circuits with the bandwidth of photonic networks. For practical applications, the efficient and controllable conversion from signal light to surface plasmons is essential. This leads to the recent developments in the polarization controlled couplings of surface plasmons. Currently, most works only tailor the orientation and arrangement of nanoslits to control the launching of surface plasmons. In this paper, we consider both the orientation and size of each slit in a one-dimensional array of nanoslit dimers. We first realize the unidirectional propagation of surface plasmons with designed wavefronts. Next, the unidirectional coupling and bi-directional coupling of surface plasmons are realized for a pair of orthogonal polarizations, respectively. This is quite different from the conventional opposite propagating surface plasmons excited by two orthogonal polarizations. The manipulation of both orientation and size of nanoslits allows additional freedom in the photon-plasmon conversions.     

Vavilov-Cherenkov like effect in metal nanofilms

The so-called surface plasmon polaritons, i.e., natural waves with a low phase velocity (much lower than the speed of light in a vacuum), exist in silver, gold, and copper nanofilms and nanowires. Electrons that are relatively slow in comparison with those that emit Cherenkov light in a homogeneous medium produce plasmons. The dispersion relations for the corresponding plasmons and the emission angles of plasmons with corresponding frequencies are calculated. It is shown that devices based on detecting Cherenkov light in nanofilms and nanowires can be used to detect low-energy electrons.     

Surface plasmon-polaritons wave fields in the vicinity of a metallic nanohole

It is shown that metal surface with a nanohole can support surface plasmon-polaritons (SPP), whose wave fields are described by Hankel functions. These plasmons can be excited by an electromagnetic wave incident at the metal surface. The optical transmission through subwavelength holes in metal films can essentially be enhanced by interaction of the incident light with surface plasmons. Dependence of excitation of the wave field of SPP on the incidence angle and on the wavelength of incident light is considered.     

Propagating anti-symmetrically coupled plasmons generation by electron beams

Propagating anti-symmetrically coupled plasmons that usually cannot be excited with incident light and radiate to far field can be efficiently generated by electron beams. An electron beam is proposed as a practical propagating anti-symmetrically coupled plasmon source due to that it couples differently to the surface plasmons than free radiation. Specifically, whispering-gallery anti-symmetrically coupled plasmons with the character of symmetrical coupled dipoles are excited by an electron beam in a nested ringlike waveguide, which is consistent with the dispersion of electron excited plasmons in an infinite-long nanowire pair.     

Light scattering from anisotropic particles: propagation,localization, and nonlinearity

Plasmon resonances and extraordinary light scatterings of a nanoparticle with radial anisotropy are studied and summarized. The coupling between localized surface plasmons and far‐field quantities is discussed. It is found that the presence of radial anisotropy redistributes the localization of plasmons and also results in certain novel phenomena in the far zone, which provide the possibility of scattering control such as electromagnetic transparency, enhanced scattering cross section, etc. The nonlinear optical response is explored in order to yield deeper physical insight into the interaction between plasmons and incident light.     

Simultaneous excitation of long and short range surface plasmons in an asymmetric structure

An asymmetric multilayer structure allowing nearly 100% simultaneous excitation of both symmetric and antisymmetric surface plasmons is proposed. It is shown that the two surface plasmons can be excited at a fixed angle of incidence with polychromatic light or with monochromatic light at different angles of incidence, depending on the design. The structure can be of interest in high-performance surface plasmon resonance sensing and in all-optical signal processing.     

New approach to spectroscopy of surface plasmons

We report a novel approach to spectroscopy of surface plasmons based on the simultaneous excitation of surface plasmons by a polychromatic light and the dispersion of light on a diffraction grating coupler of a special design. This approach shows promise for the development of new, miniaturized, spectroscopic surface plasmon resonance (SPR) sensors. Potential of this approach for SPR sensing is demonstrated in a model refractometric experiment.     

On the origin of light emission by tunnel junctions

Light emission of AlAl₂O₃-Ag structures prepared on periodic gratings was studied. It is shown that most of the observed light originates from the Ag-vacuum surface plasmons scattered by the periodic grating and surface roughness. Surface plasmons are directly excited by tunneling electrons.     

Lighting up multipolar surface plasmon polaritons by collective resonances in arrays of nanoantennas

We demonstrate the coupling of multipolar surface plasmons with photonic modes in periodic arrays of metallic nanoantennas. This coupling leads to sharp resonances known as lattice surface modes. In spite of the weak interaction of multipolar surface plasmons with light, lattice surface modes provide an efficient radiative decay channel for emitters in the proximity of the array. We observe a tenfold emission enhancement of dyes coupled to lattice resonances. Lattice surface modes light up multipolar plasmonic resonances, opening new possibilities for fluorescence spectroscopies.