Visible-transparent THz-active metamaterials based on rare-earth scandate bulk crystals

This work discusses the development of terahertz electromagnetic structures based on rare-earth scandate bulk crystals. These materials, from which gadolinium scandate is chosen as an example, offer high transparency at visible wavelengths, high resistivity for direct current, large permittivity, and a strongly anisotropic response at terahertz wavelengths with significant absorption arising from optical phonon modes. One-dimensional gratings and two-dimensional square-array geometries are explored to couple incident radiation into resonant modes, enabling control over the transmission and absorption spectra through the structure. Based on a design space exploration of the structure’s geometry, we demonstrate that it is possible to engineer its response, with near-perfect absorption achievable under certain conditions. Simulated spectra show that absorption above 90% is possible for both TE and TM polarizations. Example structures were fabricated via laser ablation and characterized using polarized terahertz transmission spectroscopy. Measured transmission spectra through these proof-of-concept structures are in good agreement with simulations, establishing rare-earth scandates as a promising platform for visible-transparent terahertz-active quasi-optical components.