Three-dimensional imaging with a terahertz quantum cascade laser

Results are presented for the first imaging system that combines the high power of terahertz (THz) quantum cascade lasers (QCLs) with the three-dimensional image reconstruction capability of computed tomography (CT). The THz QCL used in this project is a GaAs-AlGaAs bound-to-continuum superlattice design, emitting at 2.9 THz (103 μm), delivering 70 mW per facet peak power with a threshold current density of 112 A/cm². The reconstruction algorithm is based on the filtered back projection technique which has been widely used in X-ray CT. Images of phantoms made from polystyrene have been successfully reconstructed revealing both their external and internal structures with high contrast levels between different phases. Furthermore, the reconstructed images are shown to be in good quantitative agreement with the structure of the phantoms. We are currently implementing modifications to the experimental protocol and reconstruction algorithm in order to address the problems of reflection and refraction so as to extend our imaging capability to a wider range of materials.