Terahertz is an emerging research area that has flourished rapidly over the last decade. The field has drawn together experts of various disciplines including optics, optoelectronics, semiconductor physics, electronic engineering and chemistry. Terahertz radiation possesses a number of properties that makes it a promising radiation source for spectroscopy and imaging. For example, terahertz radiation is non-ionising and highly sensitive to water content. To date, there have been many attempts to build imaging systems using terahertz radiation for a wide range of potential applications including security screening and non-invasive testing of opaque objects. However, the majority of these systems encountered problems with the low power of terahertz source and as a result were only able to produce two-dimensional images of thin samples.
Figure 1: Polystyrene phantom in the shape a clown's head a) Front view, b) Top view, c) A hole with diameter of 10 mm was introduced into the sample invisible from the outside
Figure 2: Some views of the reconstructed 3D image a) The hole inside the phantom is revealed, b) The shape of the phantom is reconstructed, c) The top view shows the features of the nose and cheeks.
In this project, we have constructed a novel three-dimensional imaging system that uses a terahertz quantum cascade laser. Terahertz quantum cascade laser was experimentally realised for the first time in 2002, providing a new powerful source to generate terahertz radiation. The imaging system used an experimental protocol and reconstruction algorithm similar to X-ray computed tomography. We have successfully obtained three-dimensional images of a variety of samples, revealing both the external features and especially internal structures that are invisible from the outside.
Three-dimensional imaging with a terahertz quantum cascade laser
K. Lien Nguyen, Michael L. Johns, Lynn F. Gladden, Christopher H. Worrall, Paul Alexander, Harvey E. Beere, Michael Pepper, David A. Ritchie, Jesse Alton and Stefano Barbieri, University of Cambridge, Edmund H. Linfield, University of Leeds
Optics Express Vol. 14, Issue 6 pp2123-2129, 2006