Distinguishing different parts of objects by terahertz imaging

Abstract

Since every matter has its distinctive absorption and transmission capacity of terahertz, Terahertz time domain spectroscopy provides a powerful means to distinguish the different parts of objects. The transmittance of terahertz under different frequency can reflect the absorption distribution of the different parts of the samples. The phase shift of the terahertz wave indicates the change of optical thickness of the sample. Tree leaves, plastic ring, plastic convex lens and plastic piece with a small hole have been imaged by terahertz. As widespread samples, leaves are proved to be well imaged by terahertz wave. For the moisture content at different parts of leaves, such as mesophyll and vein, is not the same, the absorption of terahertz at these parts are quite different. At 1.4THz, the leaf's image is of good quality and the vein grids are well shown. The hole and defects in the plastic ring are also clearly shown in the THz image because the phase shifts of terahertz in different parts, such as air, defects or plastic region are not the same. It is also shown that objects with large radius of curvature are suitable for THz imagining and the scattering of THz does not affect THz phase information too much. In short, Terahertz imaging is a powerful technique to distinguish the different parts of most objects as long as the absorption of THz is not very strong.