Fluctuation-dominated materials for advanced photonics

该项目的主要目标是开发用于新型光子应用的纳米结构材料，其中设计良好的无序会引起局部电磁场的巨大波动。在这些结构中，具有最大场的“热点”的非线性响应将占主导地位，并且平均而言，强烈增加样品的非线性响应。这种方法可能会导致一种全新的“波动主导材料”——用于光子学，但也适用于其他基于波动的技术。对于两种模型系统，金属纳米多孔金纳米粒子（“纳米海绵”）和介电纳米结构硅纳米针（“纳米草”），我们建立了场增强因子和电磁模式限制，接近最先进的自上而下纳米技术所能达到的最佳值，例如，通过聚焦离子束光刻生产的纳米天线。实验近场扫描光谱和超快光电发射显微镜对制备的单个金纳米海绵的长寿命局部等离子体热点进行了解析，其分辨率低于10 nm，与理论计算结果非常吻合。目前材料科学和纳米制造的成功密切合作，一方面是最先进的光学表征方法，另一方面是相关近场光学和固态物理的详细理论分析和建模，将继续实现以下目标：(i)基于对热点形成的更深入理解，优化无序的纳米材料，以进一步增强场波动；（ii）对局部增强非线性响应进行空间和时间分辨研究的新实验，并进一步增加后者；（iii）设计、制造和研究混合材料，将具有适当量子光学特性的小的、典型的原子或分子大小的发射器，例如渗透到纳米海绵孔隙中。量子发射体与热点模式的耦合允许光学功能远远超过那些成分。最后，我们计划（iv）通过研究我们的波动主导材料与强太赫兹场的相互作用来进入完全未知的领域，强太赫兹场将调制长寿命的超局部热点的相互作用。应该强调的是，“波动主导材料”的范例已经被证实适用于金属纳米海绵和介电硅纳米草等不同的系统。这表明，潜在的物理机制将存在于许多具有定制无序的系统中，使SPP 1839成为计划研究和合作的理想背景和富有成效的环境。

The main aim of this project is to develop nanostructured materials for novel photonic applications in which a well-designed disorder induces huge fluctuations of local electromagnetic fields. In these structures, the nonlinear response of the ‘hot spots’ with largest fields will dominate and, on average, strongly increase the nonlinear response of the sample. This approach may lead to a whole new class of ‘fluctuation-dominated materials’ -- for photonics, but mutatis mutandis for other wave-based technologies as well. For two model systems, metallic nanoporous gold nanoparticles (‘nanosponges’) and dielectric nanostructured silicon nano-needles (‘nanograss’), we established field-enhancement factors and electromagnetic mode confinements that come close to the best values achievable with state-of-the-art top-down nanotechnology, e.g., in nano antenna produced via focus-ion-beam lithography. Experimental near-field scanning spectroscopy and ultrafast photoemission microscopy of a single gold nanosponge prepared within this project resolved long-lived localized plasmonic hot spots with sub-10 nm resolution in excellent agreement with theoretical calculations. The present successful close cooperation of material science and nanofabrication with, on the one hand most advanced optical characterization methods, and on the other hand a detailed theoretical analysis and modelling of the relevant near-field optics and solid-state physics will be continued with the following goals: (i) nanofabrication of materials with optimized disorder for further enhanced field-fluctuations based on a deeper understanding of hot-spot formation; (ii) new experiments for space- and time-resolved studies of the locally enhanced non-linear response and further increase of the latter; (iii) design, fabrication and investigation of hybrid materials where small, typically atom- or molecule-sized emitters with suitable quantum-optical properties are, e.g., infiltrated into nanosponge pores. The coupling of quantum-emitters to hot-spot modes allows optical functionalities far surpassing those of the constituents. Finally, we plan (iv) to enter completely unchartered territory by the study of the interaction of our fluctuation-dominated materials with strong Terahertz fields which will modulate the interaction of the long-lived, ultra-localized hot spots. It should be emphasized, that the paradigm of ‘fluctuation-dominated materials’ has been confirmed for systems as different as metallic nanosponges and dielectric silicon nanograss. This indicates that the underlying physical mechanisms will be present in many systems with tailored disorder, making the SPP 1839 the ideal context and fruitful environment for the planned research and cooperation.