Fibre-Based Fast T-ray Tomography

The aim of this project is to demonstrate THz tomography, operating at millisecond image frame rates. We propose to design, build and characterise a fast multi-channel THz tomography system without moving parts, utilising a new THz source based on short-pulse fibre lasers driven by high-power laser-diodes. The output of the fibre lasers will be combined to produce THz emission by difference-frequency generation. The character of the THz emission from the proposed source allows inexpensive pyroelectric detector arrays to be used. A large number of THz measurement channels will be realised as a parallel and re-configurable data acquisition and processing electronic system. The breakthrough in speed and facility of THz tomography will be achieved via novel solutions in: fibre lasers; THz optical train (difference-frequency generation, beam conditioning, detector geometry); signal acquisition and processing; methods for image reconstruction. The proposed technology will also open the way to fast benchtop THz tomographs with applications in a wide area of science and engineering.We propose a demonstrator experiment which will employ this novel THz tomography system to map major species' concentrations and temperature field distributions in high-pressure flames. These flames are opaque to the usual IR analysis techniques because of scattering from the soot particles, but have been shown by the applicants to be transparent to THz radiation. In addition, many of the species in these flames exhibit absorption resonances in the THz region. THz tomography therefore promises to be the only way to study high pressure flames. This has important implications in our understanding of the combustion processes in, for example, aero engines with the possibility of improving efficiency and reducing emissions of greenhouse gases. We'll demonstrate at least the following performance in the case of high-pressure flames in the presence of soot: image frame acquisition period <1ms; maps of the cross-sectional distribution of major species with spatial resolution (in area) of D2/64; maps of distribution of temperature (T~1000K) of water molecules. This project is a direct consequence of the THz Basic Technology work funded by RCUK and combines established expertise in tomography (Manchester), THz technology (Leeds) and novel laser sources (Southampton). The synergy between the currently running Basic Technology THz work and this project will allow the identification of the spectral behaviour of the chemical species in the flame under realistic conditions and indicate the best choice of spectral lines for temperature mapping. The project is a crucial step towards THz tomography for imaging of gas mixture systems and a variety of other objects, with expected strong impact on the future utility and affordability of the THz technology.