3D Nanophotonics in Artificially Structured Chalcogenide Materials

自然界中常见的蝴蝶翅膀、甲虫甲壳和乌贼交配展示的彩虹色是光的波动性质的结果，它可以对不同的颜色显示建设性和破坏性的干涉效应。我们可以在实验室中制造重复结构，其中重复周期接近光的波长，并看到类似的效果;一个众所周知的例子是来自光盘的反射，但在应用于眼镜的抗反射涂层中也可以看到相反的效果，这可以在紫色的高角度反射中看到。事实上，这些衍射反射效应的角度敏感性可以导致奇妙的彩虹反射彩色显示，而一些三维结构如蝴蝶翅膀抑制了这种角度变化;就像著名的蓝色形态种一样，它在飞行时翅膀的颜色基本上是蓝色的。在这个项目中，我们的目标是构建三维重复结构，其可以导致非常强的反射效果，同时减少通常用二维光栅和反射镜看到的角度变化。这些3D周期性材料可以有效地反射从任何角度入射的特定颜色（波长）范围的光，并基本上阻止光在任何方向上穿过材料。这些材料被称为光子带隙材料，因为它们阻挡了一个颜色带，并且因为它们具有类似于半导体带隙的特性，可以阻挡电子在某些能带中移动。虽然很难制造，但这些材料可以表现出相当惊人和有用的效果。例如，阻挡所有方向上的所有传输可以用作对强光（例如激光）的保护，或者可以使带隙对某些分子种类或污染物敏感，从而提供感测模态。在我们的团队中，我们一直在研究这些材料的光捕获特性及其对光发射的影响。例如，如果具有完全在带隙内的发射带的荧光染料分子在这样的理想材料内被激发，则它将没有发射光的路径并且保持在其激发态直到通过非辐射路径衰减。然而，如果我们通过去除少量材料来创建一个空腔，那么光发射将发生，但将被捕获在这个空腔中，直到被吸收或通过有限屏障泄漏到材料的边缘。理论上，这些存储时间可以很长，而腔体积可以做得很小，这可以导致荧光团对光的发射和吸收的强烈增强，所谓的“强耦合”是由光-物质相互作用的全量子力学处理预测的。我们将开发可靠的技术来制造这些3D光限制材料，并利用它们的新特性将光捕获在微小的“腔”和波导中，从而显示出最强的光-可能的相互作用。这些结果将产生全面的影响，从创建包含单个“原子”状发射器的新光源到最小的激光器和模仿蝴蝶翅膀反射率的材料。

The iridescent colours often seen in nature in butterfly wings, beetle carapaces and cuttlefish mating displays are a result of the wave nature of light which can show constructive and destructive interference effects for different colours. We can make in the lab repeated structures where the repeat period is close to the wavelength of light and see similar effects; a well-known example being the reflection from a compact disc but also the opposite effect is seen in the anti-reflection coating applied to spectacles which can be seen in the violet coloured high angle reflections. In fact, the angular sensitivity of these diffractive reflection effects can lead to wonderful rainbow reflective colour displays, while some three-dimensional structures such as butterfly wings suppress this angular change; as in the case of the famous blue morphospecies which maintains a largely blue wing colour while flying.In this project, we aim to build three-dimensional repeating structures that can lead to very strong reflection effects while reducing the angular changes normally seen with two-dimensional gratings and mirrors. These 3D periodic materials can effectively reflect light incident from any angle for a particular range of colours (wavelengths) and essentially block light from passing through the material in any direction. These materials are known as photonic bandgap materials because they block a band of colours and because they have properties analogous to the semiconductor bandgaps that block electrons travelling in certain energy bands. Although difficult to fabricate, these materials could exhibit quite striking and useful effects. For instance, blocking all transmission in all directions could be used as protection against bright light (e.g. lasers) or the bandgap could be made sensitive to certain molecular species or pollutants providing a sensing modality. In our team, we have been looking at the light trapping properties of these materials and their effect on light emission. For instance, if a fluorescent dye molecule with emission band entirely within the bandgap is excited inside such an ideal material then it will have no route by which to emit light and remain in its excited state until decaying by a non-radiative route. However, if we create a cavity by removing a small amount of material, the light emission will occur but will be trapped in this cavity until absorbed or leaking through the finite barrier to the edge of the material. Theoretically, these storage times can be very long while the cavity volumes can be made very small which can lead to a strong enhancement of emission and absorption of light by the fluorophore, so-called 'strong coupling' predicted by the full quantum mechanical treatments of the light-matter interaction.Finally, in this project, we will develop reliable techniques to make these 3D light confining materials and exploit their novel properties to trap light in tiny 'cavities' and waveguides thus showing the strongest light-matter interactions possible. These results will have an impact across the board from creating new light sources containing single 'atom' like emitters through to the smallest lasers and materials mimicking the reflectivity of butterfly wings.