High accuracy terahertz computed tomography using a 3D printed super-oscillatory lens

An illumination beam with a subwavelength waist and extended focal depth is ideal for terahertz computed tomography. In this paper, a binary terahertz super-oscillatory lens is proposed with a full width at half-maximum of 0.97λ, a focal length of 48λ, a focal depth of 25λ, and a numerical aperture of 0.24. It was designed using the simulated annealing algorithm, fabricated by three-dimensional printing, and applied in continuous-wave terahertz computed tomography operating at 278.6 GHz. When combined with the total variation minimisation algorithm, this setup was able to recognise a hollow cylinder with wall thickness 1.1λ and a bar of diameter 0.93λ inside a chamber, with mean errors of less than 5%. Our approach provides an effective way to enhance the resolution and reconstruction fidelity of terahertz computed tomography and to promote it as an effective tool for non-destructive testing and three-dimensional measurement.