Superconducting Detector Technology for UK Astrophysics

电磁光谱的远红外(3毫米-40微米)和中红外(40微米-5微米)区域对天文学家来说相当重要，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。光谱的MIR/FIR区域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，在远红外和中红外波段进行观测是异常困难的，因为不可能买到现成的相机。相反，天文学家必须开发自己的成像技术。这项技术必须异常敏感，不仅适用于地面望远镜，还适用于太空飞行。这项工作旨在开发新一代极其灵敏的探测器和相机，方法是用一种名为超导体的材料制造微电路。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，在一秒钟内，可以测量小于0.1瓦的照度变化，这接近于计算无线电波长的光子的能力。不幸的是，这些探测器必须冷却到100mk以下，因此需要复杂的冰箱。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。有三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急剧的超导转变来测量当红外功率被微小的独立微机械氮化硅岛吸收时发生的微小温度变化；(Ii)一种名为动力学电感探测器(KID)的设备，它本质上测量的是当电力被吸收时，磁场穿透到超导体表面的微小变化；以及(Iii)一种名为超导绝缘体超导体(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。这些设备中的每一个都可以平铺成阵列，以形成各种类型的成像系统。在节目结束时，我们将展示基于超导器件的新一代成像技术，我们将能够制造下一代地面和空间天文学所需的高灵敏度远红外和中红外相机。

The far-infrared (3mm-40um) and mid-infrared (40um-5um) regions of the electromagnetic spectrum are of considerable importance for astronomers 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, and thermal radiation from distant, highly redshifted galaxies can be found at the shortest wavelengths. The MIR/FIR region 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 far-infrared and mid-infrared wavelengths because it is not possible to buy cameras off of the shelf. Instead astronomers must develop their own imaging technology. This technology must be exceptionally sensitive, and be suitable for flying in space, in addition to being used on ground-based telescopes. The 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, in one second, it is possible measure a change in illumination of less than 0.1 attowatts, which is approaching the ability to count photons at radio wavelengths. Unfortunately, these detectors must be cooled to temperatures below 100mK, and therefore complicated refrigerators are required. The work will concentrate on understanding how to develop large-format cameras having thousands, in some cases millions, of pixels. Three devices are of specific interest: (i) a device called a Transition Edge Sensor (TES), which operates by using the sharp superconducting transition 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 Kinetic Inductance Detector (KID), which essentially measures a small change that occurs in the amount by which magnetic field penetrates into the surface of a superconductor when power is absorbed; and (iii) 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 devices can be tiled into arrays to form imaging systems of various kinds. At the end of the program, we will have demonstrated a new generation of imaging technology based on superconducting devices, and we will be able to make the highly sensitive far-infrared and mid-infrared cameras that are needed for the next generation of ground-based and space-borne astronomy.