【作者】 王国栋；

【导师】 朱永元；

【作者基本信息】 南京大学 ， 凝聚态物理， 2012， 博士

【摘要】 近十年来,随着微加工技术的不断发展和进步,人们可以在纳米的尺度对材料进行各种各样的加工制备。这些人工的纳米结构材料(超构材料)由于强烈的电磁耦合作用展现了非常独特的光学性质,它为人们提供了通过对微观结构的操控达到预期的光学性质的于段,如电磁诱导透明、隐身、透射增强、负折射等,因此受到了来自不同研究领域的研究人员的青睐。本文中对一些超构材料的光学透射性质进行了实验和理论研究,包括周期狭缝和凹槽组合的复合结构的光学透射性质；利用开口谐振环和纳米棒复合结构来实现双类电磁诱导透明的数值模拟研究；利用纳米棒-介质-纳米棒三明治结构实现的亮模—亮模模式的双类电磁诱导透明的数值模拟研究等。具体内容如下：1)对周期排列的狭缝-凹槽复合结构的光学透射性质进行了实验和理论研究,分别研究了透射峰和透射谷与凹槽的关系,包括凹槽深度和凹槽相对狭缝的位置对透射谱的影响。结果表明：上述两个因素的变化对其透射峰的影响比较小。对透射谷的影响,其中凹槽的位置变化对其影响也比较小；但凹槽的深度变化对透射谷的影响非常大,随着凹槽深度增加,其透射谷对应波长迅速的红移(波长与凹槽深度成指数关系)。为了理解凹槽深度和位置对于透射峰和透射谷截然不同的影响,分别使用唯象模型和严格耦合波模型对其进行了分析。唯象模型分析结果表明其透射峰是由于周期性凹槽和周期性的狭缝散射的表面波之间干涉加强造成的；而其透射谷则是由于干涉相消引起的。结果还表明：复合结构透射谱上金属-空气界面的瑞利异常造成的透射谷被抬高是由于周期性凹槽散射的表面波之间的干涉加强。为了给上述的唯象模型以更坚实的物理依据,用严格耦合波模型对复合结构进行了计算。计算结果与实验和数值模拟结果符合得比较一致,通过对比两个模型计算透射率的解析公式,给出了两个公式之间的对应关系,在清晰的物理图像和严谨的数学公式之间建立了一个桥梁,既严谨而又不失去物理图像。2)数值模拟研究了基于平面超构材料设计的实现双电磁诱导透明的开口谐振环(SRR)和纳米棒(nano-rod)复合结构的性质。该结构由上下两个开口谐振环和两边平行放置的两个纳米棒周期排列而成,当入射光电场在x方向时,其透射谱线形与原子物理的电磁诱导透明线形类似,这里称为类电磁诱导透明线形,透明窗口对应波长为1510nm：而当入射光的电场在y方向时,其透射谱也可以出现类电磁诱导透明线形,透明窗口对应波长为1410nm。对于两个透明窗口对应波长不同的类EIT线形,仔细研究发现,在x和y方向上形成的类电磁诱导透明耦合机制不同,即分别对应于亮模-暗模耦合和亮模-亮模耦合。为了更好地理解两个耦合模式(亮模-暗模耦合和亮模-亮模耦合)的物理意义,改变不同的结构参数下进行了模拟,结果显示两种耦合模式对参数的变化响应不同：对于亮模-暗模耦合,其透明窗口对应波长对某些参数的变化响应不敏感；对于亮模-亮模耦合,其透明窗口对应波长对参数的变化响应比较敏感。根据模拟的电场分布可以得到：对于亮模-暗模耦合,在入射光波长大于类EIT的透射峰波长时,此时被SRR激发的纳米棒的电荷分布与SRR的电荷分布表现为异性电荷之间的吸引力；在入射光波长小于类EIT的透射峰波长时,此时被SRR激发的纳米棒的电荷分布与SRR的电荷分布表现为同性电荷之间的排斥力。亮模-亮模耦合的情况与亮模-暗模的耦合一样。3)研究了三明治结构(纳米棒-介质-纳米棒)的亮模-亮模之间的耦合而形成的类电磁诱导透明现象。与平面超构材料结构相比较,三明治结构可以实现在入射光电场沿x和y方向的时候,其类EIT的透明窗口在同一个波长(1500nm)位置。这主要得益于三明治结构提供了更多的操控手段。模拟结果显示：虽然x和y方向实现了透明窗口在同一波长,但是x和y方向的类EIT线形有很大的不同,比如透明窗口的高度(即透射强度)和宽度等。此外,与平面结构的超构材料相比较,三明治结构的耦合更加复杂。对三明治结构类EIT的透射谷和透射峰的模拟结果也表明：其透射谱上形成的类EIT,一方面来自单层结构的贡献,另一方面来自层间的耦合贡献,两者的叠加形成了三明治结构透射谱上的类EIT线形。更多还原

【Abstract】 With the development of technology in the past decade, the micro structure materials (metamaterials) can be fabricated by many methods. Novel optical properties of the metamaterial have been demonstrated due to the strong interaction between the electromagnetic waves and the materials, which offers a tool to design microstructures with the expected properties, such as electromagnetically induced transparency, stealth, the transmission enhancement, negative refraction etc. Thus the field attracts researchers from various areas.The optical transmission properties of some specially designed metamaterials (1D periodic array of slit-grooves, periodic array of SRR and nanorod pair as well as sandwich structure) are studied in the thesis.The main results are as follows:1. The optical transmission properties of the periodic array of slit-groove are experimental and theoretical studied. The results show that the groove depth and location have an important effect on the transmission spectrum. While the variation of the groove depth and location has little influence on the transmission peak, the dip is very sensitive to these changes, especially the groove depth. With the increase of the groove depth, the dip is red-shifted greatly, showing an exponential relationship. In order to understand the physical mechanism of the transmission characteristic, the phenomenological model and the coupled-wave model have been used to treat the problem analytically. The results are in good agreement with each other, also in good agreement with the simulation and the experiment. The advantage of the phenomenological model lies in its clear physical picture and that of the coupled-wave model gives a rigorous mathematical result.2. In order to realize double electromagnetically induced transparency, a planar metamaterial composed of split-ring resonators (SRR) and nanorods has been studied numerically. The EIT appears whether the polarization of the incident light is in the x direction or in the y direction. The simulations reveal that when the attracting interaction between the SRR and the bar is increased the corresponding peak or valley is red-shifted; while when the repulsive interaction becomes stronger the corresponding peak or valley is blue-shifted. The mechanism of the two is different. For the x polarization, the appearance of the EIT is due the the bright mode-dark mode coupling. For the y polarization, it is due to the bright mode-bright mode coupling. The behavior of these two types EIT responses differently to the changes of the parameters.3. We also studied the double EIT in a sandwich structure, which is made of metal nanorods-media-metal nanorods, that is, a three layered structure. The nanorods in the lower layer are arranged horizontally while the nanorods in the upper layer vertically. It is shown that the EIT is mainly due to the layer with its nanorods parallel to the electric field. And the coupling between the lower and upper layer also plays some role in the transmission spectrum. The structure provides more freedom for the design.更多还原