Mass-Producible OH-Line Suppression Technologies

光传播得很快--非常快。事实上，它的速度如此之快，以至于它每秒运行3亿米的距离，或者说是地球周长的8倍。尽管光速很快，但光仍然需要很长的时间才能传播到天文距离。例如，光从太阳传播到距离我们最近的恒星--比邻星--大约需要4年。即使是光在宇宙中传播也需要如此长的时间，这意味着天文学家在观察遥远物体时实际上是在回顾过去--我们在地球上看到的星光可能是数十亿年前从这颗恒星发出的。这一事实对物理学家来说正变得非常有用，他们现在正在问自己一些非常“大的问题”，比如宇宙是如何形成的，以及暗物质和暗能量在宇宙演化中扮演了什么角色。为了回答这些问题，物理学家需要观察非常早期的宇宙，当时宇宙只有几亿年的历史。幸运的是，我们可以通过简单地观察很远的物体来获得这些观测结果。然而，当我们观察很远的物体时，会出现一个有趣的现象。宇宙在膨胀，更重要的是，膨胀的速度在增加。埃德温·哈勃在20世纪上半叶首次观察到了这一引人注目的事实，这意味着来自较远物体的光通过多普勒效应越来越多地发生红移--同样的物理现象使后退的警报声比实际音调更低。在未来，天文学家希望观测到距离我们130亿年才能到达的物体。这种光被极大地红移，关键的光谱发射线，通常只有几个毫微米的波长，实际上是我们在波长&gt；1微米的近红外中观察到的。如此高的红移给地面天文学带来了特别的问题，因为在近红外下，夜空实际上非常明亮--这是由于地球大气层中约90公里高的氧-氢(OH)分子发出的荧光。这种荧光实际上包含在整个近红外的数百条发射线中，这使得探测从感兴趣天体到达我们的光变得极其困难。然而，幸运的是，地球大气产生的荧光线在光谱上非常窄--这意味着如果它们能被一组非常精确和窄的滤光器反射，那么我们就可以接触到位于线之间的感兴趣的光。以前使用传统光学技术开发高效的OH线滤光器的尝试被证明是不成功的。然而，最近，一种使用光纤滤光器的新方法被成功地在空中演示，这种方法被称为光纤布拉格光栅。然而，目前，这些滤光片的价格高得令人望而却步，每个滤光片的成本高达数十GB k。如果这些滤光片要大规模生产，这是一个特别的缺点--如果这些滤光片要用于大型“多对象”仪器，这将需要这种能力，这些仪器将提供望远镜图像中数千个物体的光谱信息。英国目前在促进OH线抑制滤光片的大规模生产的技术开发方面处于领先地位。这些技术基于两条路线，第一条是超快激光刻字，这是一种革命性的激光制造技术，可以将三维光学电路激光写入玻璃基板；第二条是基于高度多芯光纤的使用，其中包含许多单独的玻璃通道，每个通道都可以沿光纤导光。在这个项目中，我们将把这些技术从他们目前的概念验证演示中带到可以自信地设计成未来仪器操作的点。

Light travels fast - very fast. So fast, in fact, that every second it travels a distance of 300 million metres, or eight times the circumference of the earth. As fast as the speed of light is, light can still take a VERY long time to travel astronomical distances. For example, light takes approximately 4 years to travel from the Sun to our NEAREST star - Proxima Centauri. The fact that even light can take such a long time to travel across the universe means that astronomers are effectively looking back in time when they observe distant objects - the starlight we see on earth may have been emitted from the star billions of years ago. This fact is becoming very useful to physicists, who are now asking themselves some very "Big questions" about how the universe formed and what roles dark matter and dark energy played in the evolution of the universe. To answer these questions, physicists require observations of the very early universe, when the universe was only a few hundred million years old. Luckily, we can obtain these observations - simply by looking at very distant objects.There is, however, an interesting phenomenon that occurs when we look at very distant objects. The universe is expanding, and what's more, the rate of expansion is increasing. This remarkable fact, which was first observed by Edwin Hubble in the first half of the 20th century, means that light from more distant objects is increasingly "redshifted" through the Doppler effect - the same physical phenomena that makes a retreating siren sound lower pitched than it really is. In the future, astronomers wish to observe objects which are so distant that the light has taken 13 billion years to reach us. This light is extremely redshifted, and the key spectroscopic emission lines, which normally have wavelengths of a few hundered nm, are actually observed by us in the near-infrared at wavelengths > 1 micron. Such high redshifts pose a particular problem for ground based astronomy since the night sky is actually extremely bright in the near-infrared - due to the fluorescence from oxygen-hydrogen (OH) molecules that reside about 90 km high up in the Earth's atmosphere. This fluorescence is actually contained in hundreds of emission lines throughout the near-infrared, making it extremely difficult to detect the light which reaches us from the celestial objects of interest. Luckily, however, the fluorescence lines generated by the Earth's atmosphere are spectrally very narrow - meaning that if they can be reflected by a set of very precise and narrow filters, then we can gain access to the light of interest that lies between the lines.Previous attempts to develop efficient OH-line filters using traditional optical techniques have proven unsuccessful. Recently, however, a new approach using optical fibre filters known as Fibre Bragg-gratings has been successfully demonstrated on-sky. Currently, however, these filters are prohibitively expensive - with each one costing many tens of £k. This is a particular drawback if these filters are ever to be mass-produced - a capability that would be required if these filters are to be used in large "multi-object" instruments which would provide spectral information for thousands of objects within the telescope image.The UK is currently leading the development of the technologies which will facilitate the mass-production of OH-line suppression filters. These technologies are based on two routes, the first is Ultrafast Laser Inscription - a revolutionary laser fabrication technique which enables three-dimensional optical circuits to be laser written into glass substrates, the second is based on the use of highly multicore fibres which contain many individual glass channels, each of which can guide light along the fibre. During this project, we will take these technologies from their current proof-of-concept demonstrations, to the point at which they can be confidently designed into the operation of future instruments.