金属纳米颗粒聚合体中多重Fano共振效应的研究

Fano resonances in plasmonic nanostructures are very important for reducing radiative damping, near field enhancement, and the improvement of sensing performance, where the controllable plasmon line shaping plays a key role. Compared with a single Fano resonance, a system with multiple Fano resonances can realize controllable plasmon line shaping at several spectral positions, but present studies have not consider structure symmetry, the reported results show that multiple Fano resonances dependent on the polarization direction, the modulation depth is weak, and it is hard to adjust the resonance frequencies, which are the disadvantages for multiwavelength plasmon line shaping. It is easy to modify the frequency of multipolar localized surface plasmon resonance, and they have different radiative damping. In this project, metallic nanoparticle oligomer clusters will be investigated, and we propose that polarization independence multiple Fano resonances can be generated through the coupling between multipolar localized surface plasmon resonances, as well as the adjustment of structure symmetry. In order to realize controllable plasmon line shaping at several spectral positions in the visible-near infrared region, the modulation depth of multiple Fano Resonances will be modified by adjusting the structure parameters, the radiative damping will be reduced in a wide frequency range, and the near field will be enhanced. The near field and far field properties of the oligomers will be investigated by using the finite difference time domain method (FDTD), and the physical mechanism of multiple Fano resonances will be investigated with molecular point group theory. Based on the above studies, we will investigate the applications of multiwavelength sensing. This project provides the basis for the development of multiwavelength biosensing devices based on Fano resonances.

金属表面等离激元Fano共振对降低辐射衰减、增大局域场强、提高传感性能具有重要意义，可控谱线整形是实现众多应用的核心。与单一Fano共振相比，多重Fano共振可实现多波段谱线整形，但现有体系对称性不高，多重Fano效应的产生依赖入射场偏振，且其调制深度较低，共振频率不易可控调整，限制了多波段谱线整形的应用。 多极表面等离激元共振频率容易调整、辐射衰减特性丰富。本项目提出在聚合体中引入多极表面等离激元模式耦合，同时利用聚合体的对称性，产生偏振无关的多重Fano效应。通过调节体系结构改变多重Fano共振的调制深度，有效降低辐射衰减、增大局域场强，在可见-近红外区域实现多波段可控谱线整形。本研究将利用时域有限差分法模拟体系近场和远场分布特性，并采用分子点群理论分析产生多重Fano共振的机理。最后结合以上成果，研究其在多波长传感方面的应用。本项目将为开发基于Fano共振的多波长生物传感器提供基础。

本项目针对表面等离激元Fano共振效应进行了研究，重点解决了现有体系对称性不高，多重Fano共振效应的产生依赖入射场偏振，且调制深度较低，共振频率不易可控调整等问题。提出并设计了由金属纳米棒构成的聚合体结构，可用来产生不依赖于入射场偏振的、具有较高调制深度的多重Fano共振效应，能够在多个波段有效抑制体系辐射损耗，同时其共振峰位可以方便的调整到指定波段；另外采用简单的单个劈裂纳米盘结构产生了具有较大调制深度的Fano共振效应，简化了相关光子器件的制备，并能提高器件集成度；基于上述研究，利用Fano共振对辐射衰减的抑制特性增大非线性激发源，同时采用高阶等离激元共振增大散射效率，在纳米棒聚合体及劈裂纳米环中实现了增强的二次谐波输出，可用于超快非线性光子器件的设计；此外采用电介质纳米结构Fano共振同时抑制体系辐射、非辐射损耗，能够解决表面等离激元结构无法克服的非辐射损耗问题；最后提出了一种基于偏振态的折射率传感方法，与传统基于强度光谱测量方法相比，其光谱线宽可低至亚纳米量级，传感质量因子有望超过1000。以上述成果为基础，在本项目资助下发表SCI论文8篇，申请专利1项，培养硕士生5名，其中4名取得硕士学位。