High-Performance Durable Coatings for Large Astronomical Optics

随着现代半导体探测器阵列接近理想性能，望远镜及其相关仪器的吞吐量受到光学元件涂层的限制。镜面涂层必须具有最高的反射率，能够承受极端的温度和湿度，可清洁，并且尽可能耐用。相比之下，透射光学（透镜）需要极低反射率的表面，然而，为了实现这些低光损耗，涂层也必须基本上不受污染物的影响，并定期清洗。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%，而最好的抗反射涂层可溶于水，因此难以维持。天文学并不是唯一能从光学涂层的改进中获益的学科。例如，太阳能电池阵列和太阳能聚光器也直接受益于更好的吞吐量，当考虑到全球市场时，电力转换效率提高10%的潜在经济影响将是惊人的。光学镀膜的改进不仅需要新的和更好的配方，而且需要更均匀和可靠的应用技术。加州大学天文台（圣克鲁斯）的涂层实验室，由安德鲁·菲利普斯博士领导，多年来一直致力于改善天文光学的反射和抗反射涂层。从改善涂层设施的基础设施开始，菲利普斯博士寻求两个目标：通过相对较新的技术“离子辅助沉积”和更传统的“溅射”方法，对沉积涂层的效率和均匀性进行明确的比较。这些改进还将扩展其涂层能力，包括氮化物的反应沉积，这对于目前最先进的高反射涂层至关重要。真空室内的新颖移动平台也将允许应用于大型基板区域，改善厚度和工艺均匀性。同样的新设备将用于开发用于镜子的高性能保护银涂层以及用于大型透镜的多层溶胶-凝胶抗反射涂层。这项工作的资金由美国国家科学基金会天文科学部通过其先进技术和仪器项目提供。

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.