Active Quasi-Optics for High-Power THz Science

光是电磁波最常见的表现形式。这些波不断地从无线电和电视传输，通过移动通信和WiFi，到微波、红外线、光，最后到紫外线和x射线。对于这些波的许多，紧凑，高功率，室温源已经开发：微波炉和激光是日常的例子。这个光谱的一部分，太赫兹区域，位于微波和红外波长之间，在提供光源方面技术上具有挑战性。用于无线电的晶体管设备不能足够快地切换，而且基础物理限制了红外和光学区域明亮光源的功率。我们的提议旨在提供一种紧凑、高效、在室温下在空气中运行的源，它将比其他替代品更强大、更便宜。认识这一来源将促成新的科学和促进技术发展。高功率太赫兹波可用于生物化学，生物电磁学的新领域，以及化学合成，其中太赫兹波的应用影响化学反应的进行方式。脉冲雷达需要更高的功率，例如未来的地面和星载云雷达，它们将为国家气象局和气候建模者提供输入。还有潜在的军事、安全和工业应用，通过吸收材料传输能量的可能性可能是至关重要的。这是在机场发现的扫描仪的基础，在机场，太赫兹辐射被认为不会像x射线替代品的电离辐射那样对公众健康构成威胁。来源将如何制作？这种新颖的方法依赖于一种叫做肖特基二极管的微型半导体器件，这种器件是专门设计用来产生输入频率的谐波的。换句话说，输出波是输入波的失真。我们将专门设计用于这些二极管的双用途天线。这些新型天线（我们称之为“Multennas”——倍增天线）将接收来自低频照明源天线的输入信号，将其耦合到肖特基二极管上，然后优先重新传输所需的谐波。由于每个二极管只能处理少量功率，因此有必要将许多二极管的输出组合起来以创建一个强大的电源。提出的方法是在太赫兹介质材料板上设计一组平面天线，并将肖特基二极管焊接到位。驱动太赫兹波将通过平板到达，发射的总波将是数十或数百个元素贡献的总和。“Multennas”的设计和制造是具有挑战性的精密工作，需要复杂的软件，专用设备和专业知识。来自英国两家领先研究机构——伦敦玛丽女王大学（QMUL）和STFC卢瑟福阿普尔顿实验室（RAL）的科学家和工程师们已经联手解决太赫兹源问题。拥有天线设计技能和测试设备的QMUL经验丰富的人员团队将承担项目的这些方面。最初的挑战将是改进现有的软件，使其能够模拟新的多天线结构。在RAL，该团队专门生产世界级的肖特基二极管器件，定制二极管将被设计，制造并安装到支撑板上的天线上。QMUL的其他科学家将在阵列中添加微小的光激活调谐装置，该装置由一种新型塑料制成，其特性可以被光改变。需要这些调谐器来提高整体性能，并补偿各个肖特基器件之间不可避免的变化。同样的材料将用于引入可调性的其他元素在网络的新来源。

Light is the most familiar manifestation of an electromagnetic wave. These waves extend continuously from radio and TV transmissions, through mobile communications and WiFi, to microwaves, infrared, light, an finally to ultraviolet and X-rays. For many of these waves, compact, high power, room temperature sources have been developed: the microwave oven and the laser are everyday examples. One part of this spectrum, the terahertz region, which lies between the microwave and infrared wavelengths, is technologically challenging as regards providing sources. Transistor devices, as used for radio, are not able to switch fast enough, and fundamental physics limits the power of sources that are bright in the infrared and optical regions. Our proposal aims to provide a source that will be compact, efficient, operate at room temperature in air, and which will be more powerful and cheaper than alternatives.Realisation of the source will enable new science and facilitate technology developments. High power terahertz waves can be used in biochemistry, the new field of bio-electromagnetics, and in chemical synthesis where the application of the terahertz wave affects the way that a chemical reaction proceeds. Higher power is needed for pulsed radars, for example future ground and spaceborne cloud radars that will provide input to national Met Offices and climate modellers. There are also potential military, security and industrial applications, where the possibility to transmit power through an absorbing material may be critical. This is the basis of scanners found at airports, where terahertz radiation is not believed to be a risk to public health associated with the ionising radiation from x-ray alternatives. How will the source be made? The novel approach depends on microscopic semiconductor devices, called Schottky diodes, which are designed specifically to generate harmonics of an input frequency. In other words, the output wave is a distortion of the input. We shall specifically design dual purpose antennas for use with these diodes. These novel antennas (which we have called "Multennas" - multiplying antennas) will receive an input signal from a lower frequency illuminating source antenna, couple it to the Schottky diode, and then preferentially retransmit the desired harmonic. As each diode can only handle a small amount of power, it will be necessary to combine the outputs of many diodes to create a powerful source. The proposed way is to pattern an array of flat antennas on a plate of terahertz dielectric material, and to solder the Schottky diodes in place. The driving terahertz waves will arrive through the plate, and the total emitted wave will be the sum of the contributions of tens or hundreds of elements. Design and fabrication of the "Multennas" is challenging precision work, and sophisticated software, dedicated apparatus and expertise is needed. Scientists and engineers from two of the UK's leading research institutes, Queen Mary University of London (QMUL) and the STFC Rutherford Appleton Laboratory (RAL), have joined forces to tackle the terahertz source problem. A team of experienced personnel at QMUL, who possess the antenna design skills and test facilities, will undertake these aspects of the project. An initial challenge will be to improve existing software to be able to model novel multenna structures. At RAL, where the team specialises in the production of world class Schottky diode devices, bespoke diodes will be designed, fabricated and mounted to the antennas on the supporting plate. Other scientists at QMUL will add tiny light-activated tuning devices to the array, made of a novel plastic whose properties can be changed by light. These tuners are needed to improve the performance as a whole, and to compensate for inevitable variations between the individual Schottky devices. The same material will be used to introduce tuneability to other elements in the network of the novel source.