Terahertz pulsed imaging and spectroscopy for chemical detection and security

The terahertz region, between the microwave and infrared (50 GHz-4 THz or 1.3 cm^-1-133 cm^-1), represents the last unexplored part of the electromagnetic spectrum. Absorptions observed in this region are commonly associated with intermolecular hydrogen-bonding vibrations and crystalline structure lattice vibrations. Terahertz pulsed spectroscopy (TPS) measurements obtained in both transmission and reflectance modes advance the current state-of-the-art for elucidating solid state crystalline structures such as polymorphs, hydrates, and solvates which are of interest to the pharmaceutical and chemical industries. TPS provides fundamental spectra-structure correlations for hydrogen-bonding and other organic moieties and unique insight into drug/excipient compatibility, bioavailability testing, and product dissolution. Terahertz pulsed imaging (TPI) combines TPS measurements with refractive index measurements to provide a quick and nondestructive 3D mapping technique composition and integrity of entities such as tablets in the pharmaceutical industry. In security screening, TPI can be used to image through clothing and other materials to detect concealed objects. Moreover, due to the fact that Terahertz spectra of many common plastic explosives are distinct from many confusion materials, TPS could potentially be used to identify these explosives. Various schemes (pulsed and cw) are under investigation for security applications. In this presentation, an overview of terahertz and practical implementation considerations for pharmaceutical and security applications will be discussed.