Terahertz time-domain spectroscopy (THz-TDS) is an extremely useful method to probe material electrodynamics. The THz regime comprises rich physics, enabling to determine compositional, electronic and vibronic degrees of freedom through THz spectroscopy of a material under study.
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Terahertz time-domain spectroscopy (THz-TDS) is an extremely useful method to probe material electrodynamics. The THz regime comprises rich physics, enabling to determine compositional, electronic and vibronic degrees of freedom through THz spectroscopy of a material under study. However, to study nanometre size thin films with THz-TDS, we need to overcome a large mismatch in length scales, since the THz wavelength is on the order of millimeters. A solution lies in the THz probing of metasurfaces, artificial materials made of conductive structures with length scales much smaller than the probing wavelength. Such a metamaterial induces enhanced electromagnetic field strengths near the surface, enabling nonlinear spectroscopy without the need for strong-field terahertz sources. Additionally, they provide sensitivity to the local (micron-scale) electrodynamic environment. In the ideal case, one can infer significant information about the thin film electrodynamics via the resonance frequency and dissipation in the metasurface. This thesis project comprises the optimization of terahertz (THz) resonant electric split ring resonator (eSRR) metasurfaces for enhanced-light matter coupling, suitable for material characterization. Experimental characterization is combined with finite element simulations, to obtain the transmission spectra and near-field electric, magnetic fields and current densities. In simulation, the eSRR design is optimized to obtain an up to four times stronger response at resonance than the designs described in literature. The optimized design is studied on different substrates, revealing the ability to extract a resonance even close to a substrate Reststrahlen band. This thesis concludes with characterization of the metal-insulator transition of transition metal oxide NdNiO3. From the resonance frequency and quality factor it is possible to track this phase transition from time-domain terahertz spectroscopy, thereby revealing the ability to probe extremely thin films, with an outlook on out of equilibrium studies.
