A commercial THz imaging system using Lumped Element Kinetic Inductance Detectors

探测器阵列被用于许多熟悉的技术中，以形成我们生活的世界的图像。最常见的探测器阵列被称为电荷耦合器件（CCD）阵列，构成了许多数码相机和手机相机的基础。这种探测器阵列对电磁波谱的光学区域（彩虹的颜色——从红色到蓝色）的光很敏感。然而，在人眼范围之外的电磁频谱区域中包含着丰富的信息。例如，你可能见过警用或救援直升机使用特殊摄像机在夜间搜索时拍摄的红外图像。红外光与可见光没有什么不同，在大多数情况下是由相同的机制产生的——热。如果把一块金属加热到几百摄氏度，我们会注意到它发出红光。进一步加热，它会发出黄色的光，然后变成白色。如果我们让它再次冷却，我们会看到白色的光逐渐变成黄色，黄色会逐渐变成红色，然后完全不发光。事实上，情况并非如此。这种金属现在在被称为红外的电磁光谱区域发光。我们没有观察到这一点的唯一原因是因为我们的眼睛对这种光不敏感。然而，我们可以感觉到红外光，这就是我们通常所说的热量。如果一个人的手靠近一块温暖的金属（比如家用暖气片）而不接触它，我们会觉得它是热的，因为红外线辐射使我们的皮肤变暖。如果金属冷却到室温，它仍然会发出红外线，但强度要小得多。光谱的红外区域位于可见光谱的红色区域之外，但是当我们从可见光谱进一步移动到红外区域时，我们进入了电磁光谱的太赫兹区域。太赫兹区域的频谱是非常感兴趣的研究和工业一样。例如，许多对可见光不透明的材料对太赫兹光是透明的。在这个例子中，如果有一组太赫兹探测器，就可以对表面下的物体进行成像，否则这些物体是看不见的。你可能在一些机场遇到过这样的系统，它们被用于安检目的，以检测乘客身上隐藏的物体。除了安全之外，太赫兹光的成像还有许多应用，从质量控制（例如，对封装的计算机芯片的不可见电路进行成像）到观察生物样品发出的太赫兹光，用于推断其化学成分。然而，迄今为止，开发能够感知太赫兹光的探测器已经被证明是复杂和昂贵的，因此太赫兹成像阵列在研究或工业领域并不常见。提出的研究将开发一种新型的探测器，称为集总元素动力学电感探测器（LEKID）。LEKID不仅对可见光、太赫兹光和红外光敏感，而且对紫外线和x射线也敏感。LEKID也非常容易制造成大型成像阵列，使其成为商业和工业应用的可行选择。LEKID的一个缺点是它必须冷却到非常低的温度。被称为低温的温度，LEKID操作的温度为-273摄氏度，接近物理上可能的最低温度，即绝对零度。然而，最近低温技术的发展使得实现这些低温相对简单。在这种低温下运行的探测器比室温下运行的探测器有明显的优势，其灵敏度是室温下的10000倍，而且通常要快得多。该特性首次允许以视频帧速率进行太赫兹成像。太赫兹视频的想法让许多研究科学家兴奋不已，因为他们现在有能力观察一个发射太赫兹光的系统是如何实时演变的，这在以前是不可能的。

Detector arrays are used in many familiar technologies for forming images of the world we live in. The most common detector array known as the charged coupled device (CCD) array forms the basis of many digital and phone cameras. Such detector arrays are sensitive to light in the optical region of the electromagnetic spectrum (the colours of the rainbow - red through to blue). However there is a wealth of information contained in the regions of the electromagnetic spectrum outside of the range of the human eye. For example you may have seen infrared images taken from police or rescue helicopters using special cameras searching at night. Infrared light is no different to optical light and in most cases is generated by the same mechanism - heat. If one were to heat a piece of metal to a few hundred degrees centigrade we would notice it glowing red. Heat it further and it would glow yellow then white. If we let it cool again we would see the white glow fade to yellow which would fade to red and then to no glowing at all. In fact this is not the case. The metal is now glowing in a region of the electromagnetic spectrum known as the infrared. The only reason we do not observe this is because our eyes are insensitive to this light. We can however sense infrared light and it is what we more commonly refer to as heat. If one moved their hand near a warm piece of metal (such as a household radiator) without touching it we would feel that it was hot from the infrared radiation warming our skin. If the metal were to cool back down to room temperature it would still be glowing in the infrared but now much less intensely. The infrared region of the spectrum lies just beyond the red region of the visible spectrum but as we move further past the infrared from the visible spectrum we enter what is known as the THz region of the electromagnetic spectrum. The THz region of the spectrum is of great interest to research and industry alike. For example many materials that are opaque to visible light are transparent to THz light. In this example if one had an array of THz detectors one could image objects beneath a surface that would otherwise be invisible. You may have experienced such systems in some airports where they are used for security purposes to detect concealed objects on passengers. Beyond security, the imaging of THz light has many applications ranging from quality control (imaging the invisible circuitry of an encased computer chip for example) to looking at the THz light emitted from biological samples used to deduce their chemical composition. However to date developing detectors that can sense THz light has proven complex and expensive hence THz imaging arrays are not commonplace in the world of research or industry.The proposed research will develop a new type of detector called the Lumped Element Kinetic Inductance Detector (LEKID). The LEKID is sensitive not only to optical, THz and infrared light but also ultra-violet light and X-rays. The LEKID is also very simple to fabricate into large imaging arrays making it a viable option for the commercial and industrial applications. The one drawback of the LEKID is that it must be cooled to very low temperatures. Known as cryogenic temperatures the temperature the LEKID operates at is of order -273 degrees centigrade and is close to the lowest temperature physically possible referred to as absolute zero. However, recent development in cryogenic technology has made achieving these low temperatures relatively simple. Detectors operating at these low temperatures have significant advantage over their room temperature rivals, being of order 10,000 times more sensitive and generally much faster. This property allows for the first time THz imaging at video frame rates. The idea of a THz video has excited many research scientists as they would now have the ability to watch how a system emitting THz light evolves in real time which has never before been possible.