Pollard Institute: Real-time gas sensing using terahertz quantum cascade lasers

This project will develop fast detection systems to provide the first real-time gas sensing and imaging in the terahertz (THz) region of the electromagnetic spectrum.

The THz frequency region of the spectrum lies between the infrared and microwave regions, sitting at the interface between electronic and optical technologies. Although there are numerous potential applications for THz sensing, including in atmospheric and space research, security and biomedical imaging, and industrial inspection, there has been limited practical use of THz systems outside specialised laboratories.

One key reason for this is the reliance on relatively slow thermal detectors to measure and analyse THz signals. These are inadequate for studying rapidly changing systems, such as chemical reactions, or for video-rate imaging. They are also highly susceptible to background thermal noise, which degrades imaging quality, and limits the accuracy and dynamic range of measurements. In this project, you will develop new high-speed THz gas-sensing techniques, taking advantage of recent developments in fast THz detector technology.

We will initially use a fast, and sensitive new detector system based on a field-effect transistor (‘TeraFET’) in collaboration with Goethe University Frankfurt, to detect and analyse rapidly changing chemical concentrations in a custom-built gas-cell. We will use the University’s world-leading Bragg Centre for Materials Research cleanroom facilities to develop bespoke THz quantum-cascade laser sources (QCLs), and THz photonic-molecule lasers, to target the spectral fingerprints of key atmospheric gases (e.g., O, NO, NH₃ and OH) in the 2–5 THz band, with dynamically-controllable laser emission. These will be measured in a step-scan Fourier-transform interferometry system in the School’s THz laboratories to provide spectral analysis of complex gas mixtures on microsecond timescales. In parallel, you will use TeraFET detectors to control the output power and frequency of THz QCLs, enabling their use in low-noise video-rate sensing for the first time.

This would provide key missing links in atmospheric chemistry (e.g., impact of volatile-organic compounds on the lifetimes of greenhouse gases), which currently introduce order-of-magnitude uncertainties in climate models. There are wider potential impacts though including high-speed industrial emission monitoring and control, video-rate biomedical sensing, and the first potential satellite deployment of fast and low-noise THz receiver systems.

This project would suit an applicant with a good first degree in Physics, Electronic Engineering, or an aligned subject.

Please ensure you quote this research project title in full on your application: Pollard Institute: Real-time gas sensing using terahertz quantum cascade lasers