Terahertz-frequency sensors for atmospheric chemistry and space research

当我们用现有的红外、无线电和微波传感器观察太空时，我们看到的光不到银河系的一半。大部分这种“缺失”的光位于光谱的太赫兹(THz)或远红外部分(1-10太赫兹，30-300微米波长)。事实上，地球大气层中的“隐形”气体以及恒星之间的“黑暗”尘埃和气体云都会发出独特的太赫兹指纹，提供了大气和空间科学家迫切需要的大量隐藏信息。尽管存在这种巨大的潜力，但现有的太赫兹传感器系统对于实验室以外的大多数应用来说过于庞大、脆弱和复杂，而且缺乏研究反应气体所需的灵敏度。此外，这种技术准备的缺乏限制了太赫兹系统在太空中部署的前景。英国有一个很短的时间窗口，可以投资于关键太赫兹组件和传感技术的真实世界演示，并确保在即将到来的太空任务中获得一席之地。如果没有这一点，英国研究人员将失去在这个新兴领域引领世界的潜力。在这个奖学金中，我将通过开发基于量子级联激光器(QCL)的高灵敏度系统来克服THz气体传感器以前的局限性-QCL是高度紧凑的THz辐射源，产生的功率是任何类似尺寸设备的1000倍。与以前的基于THz-QCL的气体传感方案不同，我将使用高精度的分析化学技术。这将包括使用定制的反射腔和多通道气体室，在这些气室中，太赫兹辐射反复穿过研究中的气体，估计将使灵敏度提高100倍。我还将与我在Ral Space的项目合作伙伴合作，精确控制我的太赫兹传感器的频率，与自由运行的QCL相比，光谱“指纹”的分辨率提高了10倍。总而言之，这些进步将使关键大气反应的第一次实验室观测成为可能，并为未来在卫星应用中的部署奠定基础。具体地说，我将开发第一个工作在太赫兹波段的高精度气体传感器，具有安装在卫星或国际空间站上所需的坚固、紧凑的体积和灵敏度。英国和欧洲空间研究界对太赫兹气体传感非常感兴趣，目前至少有两个飞行中的系统正在考虑中。其中包括英国领导的国际空间站太赫兹天体物理系统“塔迪斯”，以及研究高层大气气候和空间天气影响的对地观测太赫兹卫星“LOCUS”。同样的太赫兹仪器将允许超精确地监测工业或研究实验室的化学过程。微量气体将被揭示，以及高活性气体物种的组成，这是使用现有技术无法可靠区分的。关键的例子包括允许制造商确保车辆满足严格的新排放目标(欧6)，或允许大气科学家了解高层大气中发生的化学过程，提供模拟地球变化气候所需的关键缺失信息。我还将通过开发一种紧凑且便携的“工业评估器”系统，首次将这些高灵敏度技术引入相关应用环境，该系统包含高精度太赫兹气体传感所需的完整光学、电子和冷却系统。我将与我在STFC ral空间部门的项目合作伙伴一起进行一系列工业实习，以证明长路径大气气体传感的关键应用。此外，我将建立一个更广泛的学术和工业受益者网络，以建立和维持太赫兹气体传感作为英国在分析化学领域的优势。通过这一点，我将启动这项新技术的第一次商业化。

When we look into space with existing infrared, radio and microwave sensors, we see less than half the light in our galaxy. Most of this "missing" light lies in the terahertz (THz) or far-infrared part of the spectrum (1-10 THz, 30-300 micron wavelength). Indeed, the "invisible" gases in the Earth's atmosphere and the "dark" dust and gas clouds between stars all glow with distinctive THz fingerprints, providing a wealth of hidden information urgently needed by atmospheric and space scientists.Despite this great potential, existing THz sensor systems are too large, fragile and complex for most applications outside the laboratory and lack the sensitivity needed for studying reactive gases. Furthermore, this lack of technological readiness limits the prospects for THz systems being deployed in space. A short time-window is available for the UK to invest in real-world demonstrations of key THz components and sensing techniques and secure a place in forthcoming space missions. Without this, the potential for a UK researcher to lead the world in this emerging area will be lost.In this fellowship, I will overcome the previous limitations of THz gas sensors by developing high-sensitivity systems based on quantum-cascade lasers (QCLs) - QCLs are highly compact sources of THz radiation, which yield >1000 times the power of any similar-sized device.Unlike previous THz-QCL-based gas-sensing schemes, I will use high-precision analytical chemistry techniques. This will include the use of custom-made reflective cavities and multi-pass gas cells in which THz radiation passes repeatedly through the gas under study, yielding an estimated 100x improvement in sensitivity. I will also work with my project partners in RAL Space to control the frequency of my THz sensors precisely, giving 10x improvement in the resolution of spectral "fingerprints" compared with free-running QCLs. Together these advancements will allow the first laboratory observation of key atmospheric reactions and underpin future deployment in satellite applications.Specifically, I will develop the first high-precision gas sensors operating in the THz band, with the robustness, compact size and sensitivity needed for installation on a satellite or the International Space Station. The UK and European Space Research communities have taken great interest in THz gas sensing, with at least two in-flight systems currently under consideration. These include "TARDiS" - a UK-led THz astrophysics system for the International Space Station, and "LOCUS" - an Earth-observing THz satellite for studying the climate and space-weather effects in the upper atmosphere.The same THz instrumentation would allow ultra-precise monitoring of chemical processes in industry or in research laboratories. Trace gases will be revealed, together with the composition of highly-reactive gas species, which cannot be distinguished reliably using existing techniques. Key examples include allowing manufacturers to ensure that vehicles meet strict new emission targets (Euro 6) or allowing atmospheric scientists to understand chemical processes that occur in the upper atmosphere, providing critical missing pieces of information needed to model the Earth's changing climate.I shall also bring these high-sensitivity techniques into relevant application environments for the first time, through the development of a compact and portable "industrial evaluator" system, containing the complete optical, electronic and cooling systems needed for high-precision THz gas sensing. I will undertake a series of industrial placements with my project partners in the STFC RAL Space division to prove key applications within long-path atmospheric gas sensing. Furthermore, I will build a wider network of academic and industrial beneficiaries to establish and sustain THz gas-sensing as a UK strength within analytical chemistry. Through this, I will initiate the first commercialisation of this new technology.