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

光学涂层——通常由多层非晶态（玻璃状）材料组成——被广泛用于制造高反射镜、高效抗反射涂层或允许传输特定波长的光学滤光片。高反射涂层是引力波探测器的重要组成部分。这些仪器测量由引力波穿过地球引起的微小长度变化，到目前为止已经探测到来自合并黑洞和中子星的近100个天体物理引力波信号。未来，更灵敏的探测器计划扩展引力波天文学的能力，提高光学反射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晶帽层结合起来，创造出一种晶体-非晶混合涂层，从而优化涂层设计，为科学和工业应用提供许多优势。使用合适的晶体顶层可以允许入射光的很大一部分被顶层反射，从而降低存在于下面多层堆叠中的激光功率。这种降低的功率反过来可以改变对可用于堆叠的涂层材料的要求，例如允许使用具有高光吸收的材料，这些材料不耐受更高的光功率。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对光的吸收对于使未来的反射镜在低温下工作至关重要。在工业中也有许多潜在的应用，在需要高激光功率或非常小的激光束的情况下，需要耐受高光强的涂层。

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.