| Terahertz (THz) radiation offers innovative sensing and imaging technologies that can provide information unavailable through other conventional electromagnetic techniques. With the advancement of THz technologies, THz sensing will impact a broad range of areas. This thesis focuses on the use of THz spectroscopy for sensing applications including explosives detection, pharmaceutical identification and biological characterization.; Using both a THz time-domain spectroscopy (THz-TDS) system and a Fourier transform far-infrared spectrometer (FT-FIR), a THz spectral database of explosives and related compounds (ERCs) in the range of 0.1-20 THz was established. The transmission measurements show good agreement with the diffuse reflectance measurements, which are more feasible for practical applications. Density Functional Theory was employed to calculate structures and vibrational modes of several important ERCs and the calculated spectra are in good accordance with the experimental data in the 3-20 THz range. The detection and identification of the explosive RDX using diffusely reflected THz waves were also demonstrated.; THz-TDS was applied successfully for pharmaceutical study, such as investigating drug interactions, as well as identifying hydrated and anhydrous drugs, based upon the intermolecular vibrational modes of drug substances. Dehydrations and complex solid state reactions of pharmaceutical materials were studied with THz-TDS and the reaction kinetics was successfully probed. These investigations have opened new avenues for using THz technologies in pharmaceutical science and industry.; THz spectra of amino acids, purines and other biomolecules were recorded. Most of these solid-state biocompounds have THz spectral features in the 0.1-3.0 THz range. THz spectroscopy of solid-state proteins and bioactive protein micro suspensions in organic media was studied and their THz absorption features may reflect their collective vibrational modes which could be used to probe their functional 3D conformation states.; Owing to the high sensitivity of differential THz-TDS, it was successfully used to sense the minute change of biological cell monolayers. The results point to a new way for biosensing applications via differential THz-TDS.; As a powerful sensing technique, THz spectroscopy will continue to make profound contribution to the understanding of basic physics, chemistry and biology problems, as well as to the technological applications in chemical and biomedicine sensing areas. |
