Evaluation of 3D spatial resolution for Terahertz pulsed imaging systems

Terahertz pulsed imaging (TPI) has attracted considerable attention due to its wide range of applications. The spatial resolution is one of the factors used to evaluate the performance of the imaging system, and it varies between different systems and different methods. There is a need to provide calibration artefacts for evaluation of both lateral and axial spatial resolutions of TPI systems so as to enable the comparison of different systems, and to provide greater confidence in the measurement. While the evaluation of spatial resolution at a surface for 2D imaging may be straightforward, the evaluation of spatial resolution at depth for 3D imaging is more complicated. In the situation of 3D imaging, the THz signal will penetrate through layers of different materials and encounters beam diffusion, material dispersion, angle-dependent multiple reflection and transmission, and other interactions within the medium, which will ultimately affect the spatial resolution. The purpose of this paper is to present the design, fabrication, and calibration of the artefacts that enable the evaluation of lateral and axial spatial resolution both at the surface and at depth for 3D TPI systems.