超材料多级结构在太赫兹和可见光波段响应特性的研究

Study of the Response Characteristics of Metamaterial Multilayer Structures in the Terahertz and Visible Light Bands

摘要: 超材料是一种人工合成的二维超表面，具备负介电常数、负磁导率等天然材料所不具备的电磁响应。不同结构与尺寸的超材料具有不同的性能，因此超材料在生物医学、光学器件等领域有着广泛的应用。太赫兹超材料吸收器是一种将超材料应用于太赫兹波段的器件，该结构能够与自由空间阻抗相匹配，对特定频率范围内的入射电磁波能够有效的“完美吸收”。本文设计了设一款“川”字型的金属–介质–金属的“三明治”式的太赫兹超材料吸收器，利用有限元仿真软件进行建模与仿真优化，获得最优的太赫兹超材料吸收器在1~3 THz之间有一个在2.84 THz谐振吸收峰，在此频率处实现了对太赫兹波99.93%的“完美吸收”。为了进一步扩展太赫兹超材料吸收器的功能，将太赫兹超材料吸收器与金纳米颗粒相结合，即在其金属条带表面随机生长一定尺寸(30 nm ~ 70 nm)的金纳米颗粒。仿真结果表明，对于大尺寸结构的太赫兹超材料吸收器来说，小尺寸的金纳米颗粒并不会减弱其在太赫兹波段的响应。此外，通过对超材料多级结构上的单个金纳米颗粒在可见光波段的研究发现，该结构在整个可见光波段均有响应，且增强因子均在10^4以上。因此，该超材料多级结构实现了在太赫兹和可见光波段均有响应，这对于太赫兹超材料吸收器应用广度的拓展有着一定的影响。

Abstract: Metamaterials are synthetic two-dimensional metasurfaces with electromagnetic responses that are not found in natural materials, such as negative permittivity and permeability. Metamaterials with different structures and sizes have different properties, so metamaterials have a wide range of applications in biomedicine, optical devices and other fields. Terahertz metamaterial absorber is a device that applies metamaterials to the terahertz band, and the structure can match the free-space impedance to effectively “perfectly absorb” the incident electromagnetic wave in a specific frequency range. In this paper, a "Sichuan" metal-dielectric-metal "sandwich" type terahertz metamaterial absorber is designed, and the finite element simulation software is used to model and optimize the simulation, and the optimal terahertz metamaterial absorber has a resonant absorption peak of 2.84 THz between 1~3 THz, and the "perfect absorption" of 99.93% of the terahertz wave is achieved at this frequency. In order to further expand the function of the terahertz metamaterial absorber, terahertz metamaterial absorbers are combined with gold nanoparticles, i.e., they grow randomly on the surface of their metal bands of a certain size (30 nm ~ 70 nm). The simulation results show that for the large-scale structure of the terahertz metamaterial absorber, the small size of the gold nanoparticles does not weaken their response in the terahertz band. In addition, the study of individual gold nanoparticles on the multi-level structure of metamaterials in the visible light band shows that the structure responds in the entire visible light band, and the enhancement factor is above 10^4. Therefore, the multi-level structure of the metamaterial responds in both the terahertz and visible light bands, which has a certain impact on the expansion of the application breadth of terahertz metamaterial absorbers.