【作者】 胡志健；

【导师】 袁小聪；

【作者基本信息】 南开大学 ， 光学， 2010， 博士

【摘要】 表面等离激元(Surface Plasmons Polaritons, SPPs)光场局域、增强和控制在光信息处理,表面增强光谱和传感技术等方面的应用得到了广泛的关注。传统实现SPPs局域化和控制的方法一般利用金属纳米颗粒或者加工金属纳米结构。但是这种传统的方法激发SPPs具有操作复杂、很强的光散射和吸收损耗、及难以重构等方面的局限性,从而降低了SPPs的激发效率及可控性。因此研究新型全光方法替代金属结构来实现对SPPs场的激发、局域及调控具有重要的潜在应用价值。本文主要提出在均匀金属表面,全光方法局域调控表面等离激元。利用涡旋(Optical Vortices,简称OV)结构光螺旋相位特点,结合径向偏振光(“柱矢量光束”的一种)放射性轴对称及其聚焦去偏振特性,把光束整形技术引入到近场,对SPPs产生、传播、干涉等光学现象进行局域化全光调控,研究对SPPs纳米光束的整形优化,将SPPs调制为具有新颖的振幅和相位分布特点的近场光束,实现了具有螺旋相位的SPPs涡旋光。综上所述,基于光束整形与高数值孔径聚焦技术,本文主要的研究工作和创新点包括以下几个方面：本文首先设计了在满足SPPs共振条件下,线性偏振涡旋结构光束在均匀金属膜界面定点激发SPPs的有效荧光成像实验模式。利用物镜式全内反射荧光显微术(TIRFM)的倏逝波照明技术,调节实验参数满足SPR共振条件,激发金属界面处荧光分子对SPPs进行远场成像。进行定量分析了入射涡旋光束的光斑尺寸、形状、偏振、角度等入射条件对所形成SPPs局域化分布及其传播等特性的影响。其次,利用径向偏振和涡旋结构光束分布的特点,在定点激发SPPs的基础上，进一步研究了SPPs在均匀金属表面的定向传播、聚焦干涉特性。聚焦的SPPs场被调制成具有一定特殊几何图形并呈轴对称分布的超分辨SPPs点阵,实现了对SPPs场分布的优化整形。利用Richards-Wolf理论建立了高数值孔径条件下聚焦SPPs场的矢量衍射理论模型,对焦平面附件的SPPs场分布进行了详细而具体的研究。超衍射极限聚焦SPPs点阵FWHM可达到0.3λ左右。运用有限时域差分方法(FDTD),对比了以相同的入射条件下在没有金属膜样品的情况下的电场分布,进一步证明了在均匀金属膜上聚焦超分辨SPPs点阵的形成。最后,我们采用聚焦径向涡旋光束在金属膜表面对SPPs场相位结构进行调制,实现了具有螺旋相位结构的SPPs场分布。弥补于其他文献中所报道的螺旋槽和等离激元透镜结构产生SPPs旋涡的缺陷,我们提出全光方法实现远场涡旋光直接转化为高效率、动态可重构的等离激元涡旋光。基于FDTD模拟和理论分析方法,我们也详细地研究了等离激元场分布、波因廷矢量和聚焦效率。本课题通过对基于涡旋结构光束的动态SPPs荧光成像系统设计,径向偏振条件下SPPs全光调控整形、超分辨聚焦干涉效应研究,及SPPs OV的实现为研制全光控近场干涉传感器、超分辨显微成像、光学信息存储等纳米光子器件和新一代光信息处理应用提供了新的启迪。更多还原

【Abstract】 Surface plasmon polaritions (SPPs) have received considerable attentions in diverse applications, such as optical signal process, surface enhanced spectroscopy and sensor technology, with specific contributions to control, enhancement and confinement of the surface field. Traditionally, the local SPPs can be created and controlled by nano-particles or patterning metal surface. But the conventional methods have some limitations to reduce the SPPs excitation efficiency and controllability, such as operational complexity, light scattering, absorption loss and unreconfigrability. Complementary to the patterned metal surface technique, the all-optical method for generating, localizing and controlling SPPs has important potential applications.In this paper, we propose to localize and control the SPPs all-optically on the flat metal surface. Owing to the axially symmetric, depolarization and significant electric field enhancement effect of radially polarized beam and spiral phase characteristic of optical vortices (OV), the SPPs could be shaped optimally into the complex field patterns of certain amplitude and phase profile. The generating, propagating and interfering of SPPs are controlled and modulated by focused radially polarized OV beam. And the SPPs vortices with spiral phase are generated on the metal surfaceFrom the above, based on the beam shaping and the focused beam technique, the major content and result are shown as follows:Firstly, the dynamic SPPs landscapes are generated in the predefined position by using a highly focused vortex beam imaged onto a uniform flat gold (Au) metal surface where the surface plasmon resonant (SPR) angle is satisfied. Using the total internal reflection fluorescence microscopy (TIRFM) technique, Fluorescence excited by the SPPs field near the metal-dielectric interface is used to image the surface plasmon patterns experimentally. The propagation and distribution of SPPs field depended on the incident conditions, such as the size, shape and polarization of incident beam and incident angle, are analyzed quantitatively.Secondly, without metal structures, the locally induced SPPs can further be propagated following the predefined patterns to form symmetric focal spots with dimensions beyond diffraction limit. The focused SPPs field is modulated into the special axially symmetric array. FWHM of the SPPs spot on the primary intensity ring is calculated as being 0.3λ0.The proposed model of SPPs focusing by the vortex mode was described in detail based on the focused beam technique. We theoretically discuss the physics involved in the beyond-diffraction-limit focusing phenomenon and the unique characteristics of dynamic focused SPPs patterns using the vectorial diffraction theory. By performing the 3D-FDTD simulations, the proposed focusing model was verified by comparing the difference of field distributions with and without the metal film.Lastly, SPPs vortices excited by a highly focused radially polarized optical vortices beam on a metal surface are proposed with analytical and numerical verifications. Complementary to the spiral grooves and plasmonic vortex lens for generation SPPs vortices reported in literature, the proposed method reveals a direct transform from optical vortices to surface plasmonic ones with dynamic, reconfigurable and high efficiency advantages. The plasmonic field pattern, phase distributions, Poynting vector and focusing efficiency of SPP vortices are demonstrated in detail.Through the investigation of all-optical modulation and control of SPPs by optical structure light-vortex beam, the conclusions draw in this thesis is helpful to the design of near-field interference sensor, super-resolution microscopy and optical data storage applications.更多还原