【作者】 康明；

【导师】 王慧田；

【作者基本信息】 南开大学 ， 光学， 2012， 博士

【摘要】 光学和凝聚态物理是物理学中两大分支学科，而研究材料的光学特性是这两大学科的交叉领域。光在材料中传播性质是由经典的麦克斯韦方程描述。从有效媒质理论出发，方程中人们引入了描述材料与光相互作用的两个重要参数ε和μ。原则上来说，只要能够改变ε和μ，我们就可以根据需要调控光波的传播性质。虽然自然界中大多数材料都能对光响应，但受限于常规材料的限制，能够实现一些特殊的光响应一直以来是人们梦寐以求的。近年来，由特殊的人工金属纳米微结构单元构成的微结构材料，实现了在常规材料中难以实现的一些非常有趣的现象，如负折射（negative refraction）、超透镜（super lens）、隐形斗篷（invisible cloaking）等，在21世纪初的科学领域产生了深远的影响。鉴于目前对亚波长金属微结构的发展和研究，对光场的调控往往关注的是宏观的对振幅、位相（色散）的调控，很少关注对反映光场矢量特性的偏振的调控，系统的研究光与金属微结构单元构成的金属微结构材料的相互作用对于实现光场在亚波长尺度的调控有着重要的意义，特别是在亚波长尺度实现光场的偏振调控。本论文的主要内容是研究基于几类亚波长金属微结构单元构成的金属微结构材料与光场的相互作用，从而实现对光场的振幅、位相、偏振的调控。在前人已有的工作基础之上，做了如下的具体工作：（1）干涉相消现象不仅仅存在于量子体系中，也普遍的存在于经典体系中。从克服实现电磁感应透明现象的苛刻条件出发，在经典世界中寻找于量子体系中类似的现象，一直以来是人们梦寐以求的。利用亚波长金属微结构材料中的干涉相消模式，形成光传输的透明窗口，并且在透明窗口附近具有非常强的色散，从而实现对光场的位相调控，实现对光群速度的减慢。利用亚波长金属微结构材料中的干涉相消模式，设计了具有强色散的透明窗口，来类比在原子体系中的电磁感应透明机制，及Fano共振，并在实验上加以验证，为其它学科的研究提供参考和借鉴。本章中还就如何在金属微结构单元构成的金属微结构材料中实现Fano共振及推广的Fano–Feshbach共振做了细致的讨论。（2）对于构成亚波长金属微结构材料的微结构单元，人们往往关注于非常简单且具有高对称性的微结构单元的有效的电磁学响应特性，而忽略对于微结构单元本身的几何结构对称性对于整个金属微结构材料的电磁学特性的影响。利用微结构材料中的金属微结构单元的对称性来实现电磁波的非对称传输。在详细讨论圆偏振电磁波非对称传输起源的基础上，分析了实现线偏振电磁波的非对称传输的可能性；并且设计了相应的金属微结构，实现仅对线偏振电磁波的非对称传输，而对圆偏振电磁波的对称传输，并且加以验证。（3）光场的角动量分为两类：自旋角动量(SAM)和轨道角动量(OAM)。自旋角动量一般来说与光波的圆偏振相关。轨道角动量（OAM）通常与垂直于光传播轴方向平面内的位相分布相关。在亚波长金属孔中，当入射的电磁波为圆偏振时，携带自旋角动量(SAM)，在金属小孔附近（近场区域）会产生纵向场分量的涡旋，我们揭示了当入射光携带自旋角动量(SAM)时，产生纵向场分量涡旋的微观物理机制，并且发现电场和磁场的纵向分量均出现涡旋。进一步分析表明，能流的横向分量呈现与入射的圆偏振电磁波相关的涡流，这对操控微纳粒子有着潜在的应用。同时，还详细阐明了表面等离激元模式对近场光学涡旋产生所起的作用。（4）在讨论光学角动量时，我们往往的落脚点在光束的范围内讨论的，意味着光束束腰的尺度要远远大于其波长，也就是我们经常考虑的傍轴近似的情况，此种情况下光学角动量的自旋部分与轨道部分是可以分开来讨论的。当我们所研究的尺度在波长范围或是比波长范围要小，即亚波长尺度，傍轴近似不再适用，光学角动量也不在能够那么容易区分。亚波长金属微结构作为能够在亚波长尺度范围内实现与光场有效相互作用的基本单元，我们基于对亚波长金属微结构阵列中的增强透射与偏振选择特性，利用金属微结构单元在增强透射（EOT）峰处的非常强的偏振选择特性，构造了在亚波长尺度非均匀的各向异性的等效微结构材料，从而可在亚波长尺度调控光与微结构单元的相互作用，可以有效地研究在这个尺度上的光的自旋到轨道的转化问题，且从理论和数值计算详细的分析其中的物理过程，并且加以验证。从这一基本事实出发，通过简单的结构设计，实现了在无磁场情况下光的自旋态的空间劈裂，类比于电子的斯蒂芬盖-拉赫实验（S-G）；实现了在角向（旋向）体现的对入射光波自旋敏感的电场能量密度分布等非常有趣的现象。更多还原

【Abstract】 Optics and condensed matter physics are two major branch disciplines of physics,investigating the optical properties of materials is the intersection of these twodisciplines. The propagation of light in the material is described by the classicalMaxwell equations. Starting from the effective medium theory, the material equationintroduces two important parameters ε and μ in order to describe interaction betweenmaterials and light. In principle, as long as the change of ε and μ, we can control lightpropagation. Most materials can have light response, considering the limitations ofconventional materials, to achieve desired optical response is always the dream. Inrecent years, the microstructure materials composed by a special artificial metalnano-micro structure unit, achieves some very interesting phenomena, which aredifficult to achieve in conventional materials, such as negative refraction, super-lens,invisible cloaking, etc.It had a profound impact in the fields of science in the early21st century. In view of development and research of subwavlength metallicstructures, the manipulation of optical fields tend to focus on the macro-manipulationof the amplitude and phase (dispersion), and little attention to the manipulation ofpolarization, presenting the vector nature of light. Extended the manipulation ofoptical fields to subwavelength scale, the investigation to the interaction betweenlight and metal micro-structural unit is very important, especially light fieldpolarization control in subwavelength scale. The main content of this thesis is tostudy the interaction between several types of micro-structural units and the light inorder to achieve the manipulation of optical fields on amplitude, phase andpolarization.On the basis of previous works, I have done the following specific works:(1) interference cancellation phenomenon not only exists in the quantum system, aregenerally present in the classical system. Overcoming the critical conditions ofelectromagnetically induced transparency (EIT) phenomenon, to find a similarphenomenon in the classical system has been the dream. Interference cancellation mode realized by subwavelength metallic micro-structural materials, produces theformation of the transparent window, and has a very strong dispersion in the vicinityof the transparent window in order to achieve the phase control of the light field, sothe group velocity of light slows down. In analogy of the EIT mechanism in atomicsystem mechanism, and the Fano resonance, and the Fano resonance, we design thespecial subwavelength metallic structure based on the Interference cancellation mode,and verify the analogy in order to provide reference to other disciplines. In thischapter, we discuss the realization of Fano resonance and Fano-Feshbach resonancethrough the use of subwavelength metallic structure.(2) Considering to the unit of subwavelength metallic structure, people tend to focuson very simple and high symmetry unit electromagnetic response, while ignoringinfluence of the unit symmetry on the electromagnetic response. We achieve theasymmetric transmission of electromagnetic waves based on the unit symmetry. Onthe basis of a detailed discussion of the origin of asymmetric transmission forcircularly polarized electromagnetic wave, we analyze the possibility to achieve theasymmetric transmission for linearly polarized electromagnetic waves; and design thecorresponding metallic microstructure, realize asymmetric transmission only forlinearly polarized electromagnetic waves, while symmetrical transmission forcircularly polarized electromagnetic waves.(3) The angular momentum of the light field is generally divided into two categories:the spin angular momentum (SAM) and the orbital angular momentum (OAM). SAMis usually related to the circular polarization of light. OAM is usually related to thewavefront perpendicular to the light propagation axis. When the incident light iscircularly polarized, carry SAM, a longitudinal field component near the metal holespresents the spin dependent vortex, we reveal the microscopic physical mechanism ofthe longitudinal field component of the vortex, when the incident light carries SAM,and find that the longitudinal component of the electric and magnetic fields bothpresent spin dependent vortex. Further analysis show that the transverse componentof the energy flow also exhibits spin dependent vortex, which has potentialapplication in the manipulation of nano particles. At the same time, we also discussthe role of the surface plasmon polariton on the generation of near-field vortex. (4) We often discuss the optical angular momentum within the range of the beam,which means that the scale of the beam is much greater than the wavelength, i.e. theparaxial approximation, in this case the spin part and the orbital part of the opticalangular momentum can be separately discussed. When we study the scale in thewavelength range or subwavelength scale, the paraxial approximation will not be ableto apply to the optical angular momentum, which is not so easy to distinguish.Subwavelength metallic micro-structure as the basic unit can be achieved effectiveinteraction with the light field in the subwavelength scales. Based on the enhancedtransmission in subwavelength metallic structure unit with strong polarizationdependent characteristics, we construct the inhomogeneous anisotropic metamaterialsat the enhanced transmission peak, achieve the manipulation of optical fields in thesubwavelength scale, and investigate the conversion from spin to orbital angularmomentum in the subwavelength scale. The detailed theoretical and numericalanalysis of the physical processes can be verified. Starting from the basic fact,through the use of simple structure unit, we realize spatial splitting of optical spin,which can be viewed as the photonic version of a Stern-Gerlach(SG) experiment inthe absence of magnetic fields, and realize the optical spin dependent angular shift inmetallic structured metamaterials.更多还原