Terahertz Components and Systems : Metamaterials, Measurement Techniques and Applications

Abstract

THz technology has been a promising, yet problematic field in science for a long time. Up until two decades ago, the lack of fundamental components and materials operating at THz frequencies constrained its use mostly to astronomy, with very little commercial focus. Today, the field has grown remarkably, with both scientific and industrial applications pushing the development of new devices and systems to control THz radiation. Further work is necessary to overcome the region’s fundamental challenges and advance the technology on par with the rest of the electromagnetic
spectrum. This thesis aims to address new applications for THz spectroscopy, both in the frequency and time domain, as well as enhancement of THz device performance.
A new design approach for THz resonant metamaterials is proposed that aims to improve their resonant response, irrespective of individual resonator geometries.
The new approach can be applied to a wide range of already existing structures without altering the individual resonator design and relies on metamaterial cell symmetry and substrate dimensions. The design approach is used to create split-ring optical modulators, demonstrating their response is strong enough to be actuated with an LED lamp as a light source alone. The development of a multiple-angle-of-incidence, multi-wavelength THz ellipsometry
system is also presented. The utility of the system for material characterisation is demonstrated, extracting complex optical parameters of composite materials, as
well as non-homogeneous, anisotropic and highly absorptive materials in the THz range, which can be otherwise problematic to characterise. The use of the ellipsometry
system as an imaging tool for visualising and measuring internal material stresses is introduced.
Finally, the application of THz-TDS in conjunction with machine learning for waste oil quality control is investigated, introducing a new potential field of application for THz spectroscopy.