Terahertz Time Domain Spectroscopy Scattering Signatures

There has been considerable interest in the potential application of terahertz (THz) time domain spectroscopy (TDS) for a variety of problems, including the detection of explosive devices and imaging for biomedical applications. The THz regime has many advantages, including the possibility of a safe (non-ionizing) screening modality and the potential for high-resolution 3D imaging. It also has the advantage of exhibiting spectral peaks that can be used, for example, to classify explosives or detect the presence of cancerous cells. However, in addition to the chemical spectroscopic structure, many materials also produce a classic electromagnetic scattering response due to the presence of volume scatterers and/or rough interfaces present in the object. This response can serve to alter or obscure the identifying resonances, and thus it is critical to understand the nature of the scattering. In this work, random media models are devised to quantify the classical scattering response due to embedded volume inhomogeneities (in the form of spherical inclusions) and a rough surface interfaces that may occur between dielectric layers. Results are presented from THz transmission and reflection measurements of granular samples and compared with theoretical results calculated using a Quasi-Crystalline Approximation (QCA) and rough surface scattering theory. Implications of the scattering signatures and direction for future research in the THz area are presented and discussed.