Terahertz Computed Tomography of High-Refractive-Index Objects Based on Refractive Index Matching

Terahertz (THz) computed tomography (CT) is a promising technique to obtain the internal information of objects due to its properties of nonionizing and high penetration of nonpolar objects. However, THz CT is hindered by the strong refractive effect and Fresnel reflection loss when it is applied to high-refractive-index samples. In this paper, the three-dimensional image of the sample is performed in the low absorption liquid, the refractive index of which is close to the sample. This novel experimental procedure can eliminate the refractive effect and Fresnel reflection loss effectively. Together with the data processing to eliminate the liquid absorption and to restrain the artifacts, the THz CT imaging of high-density polyethylene ( n = 1.53) cylinders and cubes is achieved successfully. The internal hole and metallic foreign body are shown accurately. In addition, the defects with different sizes inside the sample are measured with refractive index matching method. It shows that THz CT imaging based on refractive index matching method has high sensitivity to detect the small defect inside the sample as small as 0.5 mm diameter.