Mass-Producible OH-Line Suppression Technologies

光速很快-非常快。事实上，它是如此之快，以至于每秒都要行进3亿米的距离，或者说是地球周长的8倍。尽管光速很快，光仍然需要很长的时间才能到达天文距离。例如，光从太阳到我们最近的星星-比邻星大约需要4年的时间。即使是光也需要这么长的时间才能穿越宇宙，这意味着天文学家在观察遥远的物体时，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星星发出的。这一事实对物理学家来说变得非常有用，他们现在正在问自己一些关于宇宙如何形成以及暗物质和暗能量在宇宙演化中扮演什么角色的非常“大问题”。为了回答这些问题，物理学家需要对非常早期的宇宙进行观测，当时宇宙只有几亿年的历史。幸运的是，我们可以通过观察非常遥远的物体来获得这些观测结果。然而，当我们观察非常遥远的物体时，会发生一个有趣的现象。宇宙在膨胀，而且膨胀的速度还在增加。这一引人注目的事实是由埃德温·哈勃在世纪上半叶首次观察到的，这意味着来自更遥远物体的光通过多普勒效应越来越“红移”--同样的物理现象使撤退的警笛声比实际音调更低。在未来，天文学家希望观察到的物体是如此遥远，以至于光需要130亿年才能到达我们。这种光是极度红移的，并且通常具有几百nm波长的关键光谱发射线实际上在波长> 1微米的近红外中被我们观察到。如此高的红移给地面天文学带来了一个特殊的问题，因为夜空实际上在近红外波段非常明亮-这是由于位于地球大气层约90公里高处的氢氧分子发出的荧光。这种荧光实际上包含在近红外线的数百条发射线中，使得我们很难检测到从感兴趣的天体到达我们的光。然而，幸运的是，地球大气层产生的荧光线在光谱上非常窄，这意味着如果它们可以被一组非常精确和窄的滤光片反射，那么我们就可以获得位于线之间的感兴趣的光。以前尝试使用传统光学技术开发高效的OH线滤光片已经被证明是不成功的。然而，最近，一种新的方法，使用光纤滤波器被称为光纤布拉格光栅已成功地在天空中演示。然而，目前，这些过滤器的价格高得令人望而却步，每一个都要花费数十万英镑。这是一个特别的缺点，如果这些过滤器是以往任何时候都是大规模生产的能力，将需要如果这些过滤器被用于大型的“多对象”仪器，将提供光谱信息的数千个对象内的望远镜images.The英国目前领先的技术发展，这将有助于大规模生产的OH线抑制过滤器。这些技术基于两条路线，第一条是超快激光雕刻-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，第二条是基于使用高度多芯光纤，其中包含许多单独的玻璃通道，每个通道都可以沿着光纤沿着引导光。在这个项目中，我们将把这些技术从目前的概念验证演示，到他们可以放心地设计到未来仪器的操作点。

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.