Materials Characterization and Interrogation using Terahertz Radiation

Abstract

Terahertz (THz) radiation is a powerful tool for characterizing materials and interrogating complex systems. The low-energy, non-ionizing nature of THz photons make it ideal for use as a non-destructive, non-contacting probe. Identification of materials by their unique THz response is possible through various absorption mechanisms, including vibrational (phonon) and rotational spectra. The Drude-like response of materials allows for non-contact electrical conductivity measurements as well. In the additive and advanced manufacturing realm, high sampling rates (kHz) and ability to extract electrical conductivity and composition makes in-situ THz imaging and spectroscopy a prime candidate for monitoring melt-pool dynamics in metal 3D printers. The fiberization of pulsed lasers systems enables the use of THz radiation to monitor oxide layer growth and characterize microstructure in challenging environments, whether ex-situ (e.g. post irradiation hot-cells) or in-situ (e.g. Transient Test Reactor, TREAT), through time of flight measurements and unique vibrational spectra of materials, providing crucial data on previously out of reach processes. While security imaging using THz radiation is already employed in airport body scanners, further miniaturization and ruggedization of THz systems enables materials characterization during field operations, adding a necessary and complementary tool to the arsenal of spectroscopic technologies available to the military and first responders. Cybersecurity is also a major focus for the coming decades; the use of THz interrogation methods to monitor integrated circuit operations provides a non-contacting, undetectable probe for system verification.