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Title: Nondestructive testing and material characterization by terahertz pulsed imaging and time-domain spectroscopy
Committee:
Dr. David Citrin, ECE, Chair, Advisor
Dr. Alexandre Locquet, ECE
Dr. Paul Voss, ECE
Dr. Nico Declercq, ME
Dr. Waymond Scott, ECE
Abstract: This dissertation argues the practical application of Terahertz (THz) imaging and time-domain spectroscopy for nondestructive evaluation (NDE) and material characterization for scientific studies and applications. For the thickness and uniformity measurement of optically thin layers on steel, post-signal-processing techniques are employed to beat the axial resolution limit to enable thickness measurements of optically thin layers. The success of resolving mill-scale films on steel with thickness down to ～ 5 µm, and identifying individual layers in multilayer paint coatings, validates the applicability of THz technology to the steel industry. In addition, THz-based techniques are also utilized for stratigraphic characterization of materials with complex layer structures. The stratigraphy of a complex sample incorporating both optically thick and thin layers is reconstructed successfully after accounting for dispersion, even in the absence of prior structural information of the material investigated. THz technology is also employed for material characterization in a noncontact, nonionizing, and non-destructive manner. We not only investigate THz birefringence and surface homogeneity of nanoporous Al2O3 films grown through a two-step electrochemical anodization process, quality control of commercial injection-molded thermoplastic components, but also characterize the optical and dielectric properties of off-the-shelf thermoplastics over a broad frequency range for high-frequency microelectronics packaging. These findings demonstrate the promising laboratory- and field-based applications of THz science and technology.
