Brightening the dim modes of plasmonic nanostructures

微小的金属结构可以充当光的WiFi天线，将单个分子或人造原子连接到可以被探测到的光上。这个项目将观察辐射光，测量它在太空中形成的模式，以了解更多关于它来自的微小结构的信息，然后利用这个模式更近距离地观察结构内部的分子。光通常以电磁波的形式在自由空间中传播。然而，就像无线电波可以在接收天线中产生电流一样，光可以使微小金属结构中的电子随着它的电场及时地来回移动。如果金属结构的形状和大小合适，电子就会与光产生共振，并且相互作用非常强烈。实际上，光被集中到金属中，然后又被散射出去。反射回来的光不是均匀的——所有的光都来自同一个点，但它以不同的强度向不同的方向辐射。光的电场方向（偏振）也随着它进入的方向而变化。这使得用普通显微镜很难检测到它。这个项目将创造新的显微镜，能够测量光随传播方向变化的方式——它的“空间模式”。通过探测不同的空间模式，我们将了解纳米结构发射的模式，并能够测量电子在金属结构中共振的不同方式。如果我们理解了共振，我们就能设计出更好的结构。将光集中到微小的体积中意味着它变得非常明亮；这使我们能够从单个分子的振动中探测到非常微弱的散射信号。这个过程被称为拉曼散射，它特别有用，因为它可以识别分子，而不需要制造化学染料来检测它们。这意味着我们可以用它来检测血液或尿液样本中的微量生物标志物进行诊断，或者筛查食物中的微量污染物。除了使用空间模式来探测与可见光对应的共振外，我们还将创造一种新的显微镜，可以在紫外线和红外光下看到，使用与自组装纳米结构很好地耦合的相同的空间模式。通过测量广泛的波长范围，可以在铝和镓等金属以及通常使用的银和金中检测到类似的共振，因为它们在可见频率上共振。使用更广泛的金属可以使结构更便宜，但也让我们区分出金属和纳米结构的特殊形状。延伸到红外线将使我们能够看到我们理论上预测的模式，但很少能够测量。能够使用紫外线使得测量与许多生物分子相匹配的共振结构成为可能，这可能在检测这些分子方面具有重要的应用。我们的工作将理解，然后控制，进入和返回微小金属结构的光的模式。它们就像光的WiFi天线一样，可以把光和分子连接起来，让我们制造新的传感器和设备。这个项目的工作将使我们更有效地“调谐”到一系列不同的纳米结构，有可能使这些微型传感器更敏感、更高效。

Tiny metal structures can act like WiFi antennae for light, connecting single molecules or artificial atoms to light that travels out and can be detected. This project will look at that radiated light, measuring the pattern it makes in space to learn more about the tiny structure that it came from - and then using that pattern to look even more closely at the molecules inside the structure. Light usually travels as an electromagnetic wave through free space. However, just as radio waves can cause an electric current in the receiving aerial, light can make the electrons in tiny metal structures move back and forth in time with its electric field. If the metal structures are the right shape and size, the electrons resonate with the light, and interact very strongly. Effectively, the light is concentrated into the metal and then scattered back out again. The light that comes back is not uniform - it all comes from the same point, but it radiates in different directions with different strengths. The direction of the light's electric field (the polarisation) also varies with the direction it's going in. That can make it very hard to detect with normal microscopes.This project will create new microscopes that are able to measure the way the light varies with the direction of travel - its "spatial mode". By detecting different spatial modes, we will learn the modes that are emitted by nanostructures and be able to measure the different ways electrons resonate in the metal structures. If we understand the resonances, it will allow us to design better structures. Concentrating the light into tiny volumes means it becomes incredibly bright; this allows us to detect very weak scattering signals from the vibrations of individual molecules. This process, known as Raman scattering, is particularly useful because it can identify molecules without needing to create a chemical dye that allows us to detect them. That means we can use it to detect tiny quantities of biomarkers in blood or urine samples for diagnostics, or screen for trace contaminants in foods. As well as using spatial modes to probe resonances that correspond to visible light, we will create a new microscope that can see in UV and infra-red light as well, using the same spatial modes that couple well to self-assembled nanostructures. By measuring across a wide range of wavelengths, it's possible to detect similar resonances in metals like aluminium and gallium, as well as the silver and gold that are normally used, because they resonate at visible frequencies. Using a wider range of metals could make the structures cheaper, but also lets us separate out what's due to the metal and what's due to the particular shape of the nanostructure. Extending into the infra-red will allow us to see modes that we have theoretically predicted, but rarely been able to measure. Being able to use UV light makes it possible to measure structures with resonances that match those of many biomolecules, which could have important applications in detecting those molecules. Our work will understand, then control, the patterns of light that go into, and come back out of, tiny metal structures. By acting like WiFi antennae for light, they can connect light to molecules, and let us make new sensors and devices. The work in this project will let us "tune in" more efficiently to a range of different nanostructures, potentially making these miniature sensors more sensitive and more efficient.