Exploring New Deposition Processes for Astronomical Coatings

该项目将改进天文反射镜的光学涂层。天文望远镜的主要目的是收集尽可能多的光进行分析。然而，每次反射时，镜面都会吸收一定量的光。目前，标准的镜面涂层是铝，每个表面大约有10%的损耗。由于现代望远镜通常使用三个或更多的镜子，这导致30%或更多的光丢失。银是比铝更好的反射器，每次反射只损失约3%的光。镀银反射镜将在光收集方面取得显著的成果，而建造一个新的更大的望远镜的成本只是其中的一小部分。然而，银容易失去光泽和腐蚀，因此必须用透明的保护层覆盖。近年来，在合适的银镜涂层方面取得了进展，但仍然缺乏一种可以使用多年的顶级保护层。该项目将通过探索两种新的薄膜沉积技术来解决这一缺失的部分，这两种技术有望显著延长银镜涂层的使用寿命。虽然这个项目专门针对望远镜反射镜的涂层，但它在其他领域也有潜在的用途，比如提高太阳能聚光器的效率。该项目将安装专门的设备，在现有的真空室中探索新的薄膜沉积技术。第一种新的沉积方法是高功率脉冲磁控溅射（HiPIMS）。在传统的溅射中，原子被离子（带电原子）从源材料上撞下来，然后落在被涂覆的表面上。HiPIMS通过在非常短的脉冲中产生高功率的离子来改进这一点，从而为离子提供更多的能量。因此，被敲除的原子也处于更高的能量，这有助于压缩生长的薄膜。第二种新技术是过滤阴极电弧（FCA）沉积，其中电弧直接进入源材料使材料蒸发。流出的气流既含有原子，也含有粒子，因此使用磁场使气流弯曲。这过滤掉了粒子和中性原子，产生了非常纯净的高能电离原子流。在这个项目中，这两种高能工艺将用于制造特殊材料，如类金刚石碳和某些氮化物。这些材料具有透明保护层所需的特性。此外，这些技术可以以非常快的速度沉积银，从而提高反射率。将制作保护银镜面涂层的样品，然后放置在恶劣的环境中，以表明它们在望远镜上能坚持多久。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project will improve optical coatings for astronomical mirrors. The primary purpose of astronomical telescopes is to gather as much light as possible for analysis. However, at every reflection, a certain amount of light is absorbed by the mirror surface. Currently, the standard mirror coating is aluminum, with roughly a 10% loss at each surface. Since modern telescopes usually use three or more mirrors, this results in 30% or more of the light being lost. Silver is a significantly better reflector than aluminum, losing only about 3% of the light at each reflection. Silver coated mirrors would result in significant gains in light collection at a fraction of the cost of building a new larger telescope. However, silver is prone to tarnishing and corrosion, so it must be covered by transparent protective layers. Progress towards suitable silver mirror coatings has been made in recent years, but a top protective layer that can hold up to years of use is still lacking. This project will address that missing piece by exploring two new thin film deposition techniques that are expected to extend the lifetimes of silver mirror coatings significantly. While this project is aimed specifically at coatings for telescope mirrors, it has potential use in other areas, such as increasing the efficiency of solar concentrators for energy production.This project will install specialized equipment for exploring new thin film deposition techniques in an existing vacuum chamber. The first new deposition method is High-power Impulse Magnetron Sputtering (HiPIMS). In conventional sputtering, atoms are knocked off source material by ions (charged atoms), and then land on the surface being coated. HiPIMS modifies this by creating the ions in very short pulses at high power, giving the ions more energy. Consequently, the atoms knocked out are also at higher energy, which helps compact the growing thin film. The second new technique is Filtered Cathodic Arc (FCA) deposition, in which an electric arc going directly into the source material vaporizes the material. The outflowing stream contains particles as well as atoms, so a magnetic field is used bend the stream. This filters out particles and neutral atoms, resulting in a very pure stream of high-energy ionized atoms. In this project, these two high-energy processes will be used to make specialized materials such as diamond-like carbon and certain nitrides. These materials have the properties that are needed for transparent protective layers. In addition, these techniques can deposit silver at very fast rates, which improves reflectivity. Samples of protected-silver mirror coating will be made, and then placed in a harsh environment to indicate how long they will endure on telescopes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.