金属纳米间隙复合型表面等离激元自发辐射耦合增强效应研究

The project aims at the bottleneck problem that the enhancement of the spontaneous emission rate and the emission efficiency cannot be achieved simultaneously for the design of the devices relying on the enhancement of the spontaneous emission with surface plasmon polaritons (SPPs), and aims at the limitation on the study of physical mechanisms faced by the present numerical computational approaches of electromagnetic field and the experimental study methods. Through the establishment of microscopic dynamics analytical models, we are then able to clarify the physical mechanism in the simultaneous enhancement of the emission rate and emission efficiency with the hybrid-type SPPs in metallic nanogap-resonance structures at a rigorous and quantitative level, so as to achieve an efficient design of devices and to solve the bottleneck problem. On this basis, aiming at the important application of the high-sensitivity molecular sensing with Raman or fluorescence spectra, the project will finish the design and experimental demonstration of the devices with a broad band enhancement of the emission rate and emission efficiency and with directional radiation, to achieve a high sensing sensitivity of few or single molecules. Besides, the project will further develop the electromagnetic theories relevant to the microscopic model of hybrid-type SPPs, including the radiation and scattering theories of electromagnetic modes, quasi normal mode theories of resonant structures, and the rigorous coupled wave analysis under arbitrary curved coordinate system, to solve the difficulty in accurately matching the electromagnetic boundary condition of nanoscale gaps and the bad convergence arising from the extreme strong or even singular electromagnetic field in the metallic nanogap faced by the present numerical computational approaches.

项目针对目前表面等离激元（SPP）自发辐射增强器件设计中面临的提高辐射速率与提高辐射效率相互制约的瓶颈问题，以及目前电磁场数值计算方法、实验研究手段等在物理机制研究方面受到的限制，通过建立微观动力学解析模型，实现在严格、定量的水平上明确金属纳米间隙-谐振结构中复合型SPP实现辐射速率、辐射效率同时增强的物理机制，从而有效地指导器件设计，从根本上解决该瓶颈问题。在此基础上，针对高灵敏度拉曼及荧光光谱分子传感重要应用，完成辐射速率、辐射效率宽波段增强以及定向辐射器件设计及实验验证，实现少数分子甚至单分子水平的传感灵敏度。此外，将进一步发展复合型SPP微观模型相关的电磁场理论，包括电磁模式辐射及散射理论、谐振结构准简正模式理论、以及任意曲线坐标系下严格耦合波分析算法，解决目前电磁场数值计算方法遇到的纳米尺度间隙电磁场边界条件精确匹配困难、纳米间隙内极强甚至奇异性局域电磁场导致的收敛困难问题。

项目围绕金属纳米间隙结构中复合型表面等离激元（SPP）自发辐射增强效应，开展了相关的机理分析、器件设计和实验验证工作。考虑各类金属纳米间隙和谐振结构组成的支持复合型SPP的结构，通过建立微观动力学解析模型，给出结构自发辐射特性参数的解析表达式，明确了结构中复合型SPP实现提高辐射速率、提高辐射效率、提高电场增强因子、宽波段自发辐射增强以及远场定向辐射等的物理机制，获得了优化的器件设计结果。此外，进一步发展了复合型SPP微观动力学模型相关的电磁场理论。建立了金基底纳米槽波导中SPP波导模式的解析模型。建立了色散、损耗金属纳米谐振腔耦合系统的严格的准简正模式（QNM）耦合理论，以及纳米颗粒扰动回音壁微腔QNM及奇异点简并的解析模型，提出了基于周期波导模式本征值问题的QNM数值求解算法，拓展了QNM理论的相关应用。提出了适用于任意曲面边界三维光子结构的坐标变换傅立叶模式法。针对高灵敏度拉曼及荧光光谱分子传感重要应用，完成了复合型SPP自发辐射增强效应及器件的实验验证。提出了一种金属纳米间隙尺寸及间隙内荧光分子位置精确可调的金基底-PMMA胶-荧光分子-PMMA胶-金纳米棒天线结构，实验验证了具有纳米间隙的光学天线结构中复合型SPP自发辐射增强效应，为纳米间隙内少数分子甚至单分子水平的荧光传感提供了精确可控的技术手段。基于光力捕获形成水溶液中金纳米立方体及金纳米球纳米间隙结构，实验验证了纳米颗粒及纳米间隙SPP的自发辐射增强效应引起的极低浓度下分子拉曼散射增强。采用金纳米球-银纳米线-量子点耦合结构，实验验证了纳米间隙内SPP引起的量子点荧光自发辐射增强并激励出沿银纳米线传播的SPP。实验验证了不同基片对单量子点单光子荧光发射特性的调控。项目成果将为高灵敏度分子光谱传感、高亮度及高速纳微光源等相关应用提供理论和技术支持，并促进电磁场理论、微纳光学、表面等离激元光学等相关学科的发展。