High-Performance Durable Coatings for Large Astronomical Optics

随着现代半导体探测器阵列接近理想的性能，望远镜及其相关仪器的吞吐量受到光学元件涂层的限制。 镜面涂层必须具有可达到的最高反射率，能够承受极端温度和湿度，可清洁，并尽可能耐用。 相比之下，透射光学器件（透镜）需要极低反射率的表面，但实现这些低光损失的涂层还必须基本上不受污染物和定期清洁的影响。 今天最好的涂料在这些方面还有很多需要改进的地方。 铝仍然是标准的望远镜反射镜涂层，尽管在光学红色光谱区域损失高达10%，而最好的反射镜涂层是可溶于水的，因此难以维护。天文学不是唯一的学科将受益于光学涂层的改进。 例如，太阳能电池阵列和太阳能聚光器也直接受益于更高的产量，在全球市场上考虑时，电转换效率提高10%的潜在经济影响将是惊人的。光学涂层的改进不仅需要新的更好的配方，还需要更均匀和可靠的应用技术。 由Andrew菲利普斯博士领导的加州大学天文台（圣克鲁斯）的涂层实验室多年来一直致力于改进天文光学的反射和抗反射涂层。菲利普斯博士从改进其镀膜设备的基础设施开始，寻求追求两个目标：通过称为“离子辅助沉积”的相对较新的技术与更传统的“溅射”方法沉积涂层的效率和均匀性的明确比较。 这些改进还将扩展其涂层能力，包括氮化物的反应沉积，这对被认为是当前技术水平的高反射涂层至关重要。真空室内的新型移动台也将允许应用到大面积基板上，从而改善厚度和工艺均匀性。同样的新设备将用于开发高性能的镜子保护银涂层以及大型镜头的多层溶胶-凝胶抗反射涂层。 这项工作的资金由NSF的天文科学部通过其先进技术和仪器计划提供。

With modern semiconductor detector arrays approaching near-ideal performance, the throughput of telescopes and their associated instrumentation is becoming limited by the coatings applied to the optical components. Mirror coatings must have the highest reflectivity attainable, be able to withstand extremes in temperature and humidity, be cleanable, and be as durable as possible. Transmissive optics (lenses), by contrast, require extremely low-reflectivity surfaces, yet the coatings to achieve these low light losses must also be essentially impervious to contaminants and periodic cleaning. Today's best coatings leave much to be desired in these regards. Aluminum is still the standard telescope mirror coating, despite losses as high as 10% in the optical red spectral region, while the best antireflection coating is soluble in water and therefore difficult to maintain.Astronomy is not the only discipline that would gain from improvements to optical coatings. Solar arrays and solar concentrators, for example, also benefit directly from better throughput, and the potential economic impact of a 10% gain in electrical conversion efficiency would be astounding, when considered on the worldwide market.Improvements in optical coatings require not only new and better formulations but also more uniform and reliable application techniques. The coatings lab at the University of California Observatories (Santa Cruz), headed by Dr. Andrew Phillips, has been engaged in efforts to improve both reflective and anti-reflection coatings for astronomical optics for a number of years. Starting with improvements to the infrastructure of their coating facilities, Dr. Phillips seeks to pursue two goals: a definitive comparison of the efficiency and uniformity of depositing coatings through the relatively new technique called "ion-assisted deposition" vs. the more traditional approach of "sputtering". The improvements will also extend their coating capabilities to include the reactive deposition of nitrides, which are critical to the highly reflective coating considered to be the current state of the art. A novel moving stage inside the vacuum chamber will also allow application onto large substrate areas with improved thickness and process uniformity. This same new equipment will be used to develop both high-performance protected-silver coatings for mirrors as well as multi-layer sol-gel anti-reflection coatings for large lenses. Funding for this work is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.