Ultra-sensitive Detectors for Astronomy

电磁光谱的亚毫米波(3毫米-300微米)和远红外(300微米-20微米)区域对天文学具有相当重要的意义，因为它们包含了关于凉爽、光学黑暗的宇宙的丰富信息。例如，宇宙微波背景辐射是大爆炸的遗迹，可以在最长的波长上找到，而来自遥远的、高度红移的星系的热辐射可以在最短的波长上找到。这部分光谱还包含来自众多分子和原子物种的数千条谱线，这些谱线对于研究恒星形成区域的化学非常重要。然而，在亚毫米波、远红外和波长进行观测是格外困难的，因为不可能从货架上买到足够灵敏的相机。相反，天文学家必须开发自己的成像技术。这些探测器必须是高灵敏度的，并且必须冷却到500mK以下的温度。此外，这些仪器必须坚固耐用，并能够在太空中飞行。这项拟议的工作旨在通过用称为超导体的材料制造微电路来开发新一代极其灵敏的探测器和相机。超导体具有这样的特性，即其电阻在某一临界温度以下降至零，而磁通被排出。事实上，超导态是一种特殊的物质状态，具有许多奇怪的性质。通过用超导体Nb、Ta、Al和Mo制造微电路，并通过使用现代硅微机械加工技术，可以制造具有特殊性能的探测器。例如，我们最新的红外探测器能够在1000万英里的距离上探测到灯泡打开和关闭的时间仅为1秒。这项工作将集中在了解如何开发具有数千像素，有时甚至数百万像素的大画幅相机。有四种设备特别令人感兴趣：(I)一种名为转变边传感器(TES)的设备，它的工作原理是利用超导体的急剧转变来测量当红外功率被一个微小的独立的微机械氮化硅岛吸收时发生的微小温度变化；(Ii)一种名为冷电子测辐射热计的设备，它使用固态制冷来实现超低噪声功率检测；(Iii)一种名为动力学电感检测器(KID)的设备，它本质上测量的是超导体吸收电力时磁场穿透到表面的微小变化量；以及(Iv)一种名为超导绝缘体超导(SIS)混音器的设备，它使用极薄的超导和绝缘材料层来制造二极管，可以用来建造高灵敏度的无线电接收器。这些设备类型中的每一种都可以包装成阵列以形成各种类型的成像系统。事实上，近年来在天文学方面取得的惊人科学发现，正是因为我们有能力通过使用这些微小的亚微米设备来探测来自大型射电望远镜的非常微弱的信号。在节目结束时，我们将展示基于超导设备的新一代成像技术，这种技术将可用于构建下一代地面和空间天文学所需的高灵敏度亚毫米波和远红外相机。

The submillimetre-wave (3mm-300um) and far-infrared (300um-20um) regions of the electromagnetic spectrum are of considerable importance for astronomy because they contain a wealth of information about the cool, optically dark Universe. For example, the Cosmic Microwave Background radiation, which is a relic of the Big Bang, can be found at the longest wavelengths, whereas thermal radiation from distant, highly redshifted galaxies can be found at the shortest wavelengths. This part of the spectrum also contains thousands of spectral lines from numerous molecular and atomic species, which are important for studying the chemistry of regions where stars are being formed. It is exceptionally difficult, however, to make observations at submillimetre-wave and far-infrared and wavelengths because it is not possible to buy sufficiently sensitive cameras off of the shelf. Instead astronomers must develop their own imaging technology. These detectors must be highly sensitive, and must be cooled to temperatures of below 500mK. In addition, the instruments must be rugged, and capable of being flown in space. The proposed work aims to develop a new generation of extremely sensitive detectors and cameras by fabricating microcircuits out of materials called superconductors. Superconductors have the property that their electrical resistance falls to zero below some critical temperature, and magnetic flux is expelled. Indeed, the superconducting state is a special state of matter, and has many curious properties. By fabricating microcircuits out of the superconductors Nb, Ta, Al, and Mo, and by using modern Si micromachining techniques, it is possible to make detectors having exceptional properties. For example, our most recent infrared detectors are capable of detecting a light bulb being turned on and off for just 1 second at a distance of 10 million miles. The work will concentrate on understanding how to develop large-format cameras having thousands, and in some cases millions, of pixels. Four devices are of specific interest: (i) a device called a Transition Edge Sensor (TES), which operates by using the sharp transition of a superconductor to measure the minute change in temperature that occurs when infrared power is absorber by a tiny free-standing micro-machined silicon nitride island; (ii) a device called a Cold Electron Bolometer, which uses a solid-state refrigeration to achieve ultra-low-noise power detection; (iii) a device called a Kinetic Inductance Detector (KID), which essentially measures a small change that occurs in the amount by which a magnetic field penetrates into the surface of a superconductor when power is absorbed; and (iv) a device called a Superconductor Insulator Superconductor (SIS) mixer, which uses extremely thin layers of superconducting and insulating material to create diodes, which can be used to construct highly sensitive radio receivers. Each of these device types can be packed into arrays to form imaging systems of various kinds. Indeed, the wonderful scientific discoveries that were achieved in astronomy, in recent years, were only made possible by our ability to detect very weak signals coming from large radiotelescopes by using these tiny sub-micron devices. At the end of the program, we will have demonstrated a new generation of imaging technology based on superconducting devices, which will be available to construct the highly sensitive submillimetre-wave and far-infrared cameras that are needed for the next generation of ground-based and space-borne astronomy.