Controlled excitation of quantum emitters by nonlinear plasmonic nearfields

即使在最好的显微镜物镜的焦点上，光场也类似于具有空间平坦波前的平面波。这使得偶极近似在模拟分子、量子点和蛋白质与光的相互作用时无处不在。超出这个近似的影响，例如不同的光学选择规则，只能通过在亚波长长度尺度上弯曲的光场来实现。等离子体能够通过金属纳米结构的精心安排产生这样的雕刻场。然而，光场的空间形状是相当固定的，因为它是由材料定义的。这使得切换空间形状变得困难，例如证明其对大型多色系的激发光谱的影响。在这个项目中，我们建议使用非线性等离子体来克服这一限制。等离子体纳米结构内部的场增强增强了三次谐波产生等非线性效应。虽然线性等离子体已被很好地理解，但在非线性等离子体中仍有许多问题有待解决。这个项目有助于解决两个关键问题：贵金属中的三次谐波是如何与电子能带结构和职业功能联系起来的？这个问题的答案将允许我们调整局部非线性响应，例如，局部加热电子气体。第二个主题是混合非线性等离子体结构，其中局部产生的三次谐波将被用来激发单量子发射器。结合这些，我们的等离子体纳米结构将作为光源，其空间排列可通过定制的非线性在亚波长长度尺度上可控。我们设想在该光源附近放置具有空间扩展激发态的大型多色系统，例如光收集复合物或H聚集体。我们的新光源将允许超越偶极近似的光谱学，我们希望能够阐明，例如量子相干性在生物系统中的作用。

Even in the focus of the best microscope objective the optical field resembles a plane wave with a spatially flat wave front. This makes the dipole approximation ubiquitous when modelling the interaction of molecules, quantum dots and proteins with light. Effects beyond this approximation, for example different optical selection rules, are accessible only with optical fields that are curved on a sub-wavelength length scale. Plasmonics is able to generate such sculptured fields by elaborate arrangements of metallic nanostructures. However, the spatial shape of the optical field is rather fixed, as it is defined by the material. This makes it difficult to switch the spatial shape, for example to demonstrate its influence on the excitation spectrum of a large multi-chromophoric system.In this project we propose to use nonlinear plasmonics to overcome this limitation. Nonlinear effects such as third-harmonic generation are boosted by the field enhancement inside plasmonic nanos-tructures. While linear plasmonics is rather well understood, in nonlinear plasmonics still many questions are open. This project contributes to two key questions: How is third-harmonic generation in noble metals connected to the electronic band structure and the occupation function? The answer to this question will allow us to tune the local nonlinear response by, e.g. locally heating the electron gas. The second topic are hybrid nonlinear plasmonic structures in which the locally generated third harmonic will be used to excite single quantum emitters. In combination, our plasmonic nanostructure will act as light source with a spatial arrangement that is controllable on a sub-wavelength length scale by a tailored nonlinearity. We envision placing large multichromophoric systems with spatially extended excited states near this light source, such as light-harvesting complexes or H aggregates. Our novel light source will allow spectroscopy beyond the dipole approximation which we expect to shed light on, e.g. the role of quantum coherence in biological systems.