Establishing the design and development of novel crystalline-amorphous hybrid optical coatings for precision measurements and frequency standards

光学涂层-通常由交替的非晶（玻璃状）材料的多个薄层组成-被广泛用于形成高反射镜、有效的抗反射涂层或允许特定波长透射的滤光器。高反射涂层是引力波探测器的关键部分。这些仪器测量引力波穿过地球引起的微小长度变化，迄今为止已经探测到近100个来自黑洞和中子星合并的天体物理引力波信号。未来，更灵敏的探测器计划扩大引力波天文学的能力，提高光学镜涂层的性能是这些新探测器的关键挑战。该项目旨在将传统的多层光学涂层与薄的结晶帽层结合联合收割机，创建结晶-非晶混合涂层，从而实现优化的涂层设计，具有许多科学和工业应用的优势。使用适当的结晶顶层可以允许大部分入射光被顶层沿着反射，从而降低存在于下面的多层堆叠中的激光功率。这种降低的功率又可以改变对可以在堆叠中使用的涂层材料的要求，例如允许使用具有高光学吸收的材料，其将不耐受较高的光功率。这在引力波探测器中有直接的应用，在引力波探测器中，最大限度地减少涂层中的光吸收对于允许未来的镜子在低温下工作至关重要。在工业中也有许多潜在的应用，其中在需要高激光功率或非常小的激光束的情况下需要耐高光强度的涂层。

Optical coatings - typically consisting of multiple thin layers of alternating amorphous (glass-like) materials - are widely used to form highly reflective mirrors, efficient anti-reflective coatings or optical filters which allow particular wavelengths to be transmitted. Highly-reflective coatings are a key part of gravitational wave detectors. These instruments measure tiny changes in length caused by gravitational waves passing through the Earth, and have so far detected almost 100 astrophysical gravitational wave signals from merging black holes and neutron stars. Future, more sensitive detectors are planned to expand the capabilities of gravitational wave astronomy, and improving the performance of optical mirror coatings is a critical challenge for these new detectors. This project aims to combine a traditional multilayer optical coating with a thin crystalline cap-layer, creating a crystalline-amorphous hybrid coating, enabling optimised coating designs with a number of advantages for both scientific and industrial applications.Using an appropriate crystalline top-layer can allow a significant fraction of the incoming light to be reflected by the top layer along, reducing the laser power present in the multi-layer stack below. This reduced power can in turn change the requirements for the coating materials which can be used in the stack, for example allowing the use of materials with a high optical absorption which would be intolerant to higher light power. This has direct applications in gravitational wave detectors, where minimising the absorption of light in the coatings is essential to allow future mirrors to operated at cryogenic temperatures. There are also many potential applications in industry, where coatings which are tolerant of high light intensity are required in situations where high laser powers, or very small laser beams, are required.