An integrated gas spectroscopy system -- combining TeraFETs and THz QCLs to enable 2--5-THz power detection and heterodyne mixing

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Approximately half the light in our galaxy lies in the terahertz (THz) or far-infrared part of the spectrum (0.3-10 THz, 30–1000-micron wavelength), and yet it is undetectable using existing satellite-borne instrumentation. Unlocking this part of the spectrum would reveal the processes that drive the formation of stars and planets and would fill important gaps in our understanding of the chemistry of climate change in the Earth’s atmosphere.Despite this great potential, THz systems are generally too large, fragile, and complex for use outside the laboratory. A key limitation is the availability of good quality THz detectors, as existing devices either have poor sensitivity at higher THz frequencies, require extreme cooling, or are too slow to study chemical reactions as they happen. In this programme, we will overcome these issues by developing the first compact, sensitive, and fast THz detector systems that are suitable for trace-gas detection and integration with satellite payloads. These will be based on “TeraFET” devices, advanced field-effect transistor structures, integrated with THz antennas. They have established themselves in the last years as powerful detectors of radiation over the entire THz spectrum. They can be fabricated entirely in foundries with the technologies of mainstream microelectronics, with many ensuing benefits such as a high performance reproducibility and the possibility to build detector arrays. TeraFET devices will be designed to detect radiation precisely at frequencies around 2.0, 3.5 and 4.7 THz, corresponding to the “fingerprints” of important gas species (e.g., O, OH, CO, NO and HO2), which are key to observing chemical processes in deep space and the Earth’s upper atmosphere. We will undertake detailed characterisation of the sensitivity, noise and frequency response of these new devices using purpose-built THz quantum-cascade laser (THz QCL) sources – highly compact sources of THz radiation, yielding >1000 times the power of any similar-sized device. TeraFETs will be established both as direct detectors of THz radiation, and also as mixers for future use in satellite-borne receiver systems. We will develop the first compact and integrated THz systems containing a QCL and TeraFET device, mounted into the same thermal packaging, enabling in situ targeted monitoring and control of THz power for the first time. We will demonstrate a purpose-built THz trace-gas detection system and demonstrate the first targeted detection of THz gas fingerprints using a compact narrowband detector suitable for integration and packaging.