Superconducting terahertz (THz) metamaterial (MM) made from niobium (Nb) film has been investigated using a continuous-wave THz spectroscopy. The quality factors of the resonance modes at 0.132 THz and 0.418 THz can be remarkably increased when the working temperature is below the superconducting transition temperature of Nb, indicating that the use of superconducting Nb is a possible way to achieve low loss performance of a THz MM. In addition, the tuning of superconducting THz MM by a magnetic field is also demonstrated, which offers an alternative tuning method apart from the existing electric, optical and thermal tuning methods.
We demonstrate how terahertz time-domain spectroscopy (THz-TDS) operating in reflection geometry can be used for quantitative conductivity mapping of large area chemical vapour deposited graphene films through silicon support. We validate the technique against measurements performed using the established transmission based THz-TDS. Our through-substrate approach allows unhindered access to the graphene top surface, and thus, as we discuss, opens up pathways to perform in-situ and in-operando THz-TDS using environmental cells.
Multifunctional terahertz (THz) devices are crucial for the development of practical applications such as high-speed communications, spectroscopy, and imaging, but their expansion is still requiring efficient agility functions operating in the THz domain. Chalcogenide phase change materials (PCMs) with broadband responses and nonvolatile and reversible transitions between dielectric and metal-like phases were successfully investigated as agile elements in photonics or electronics applications, but their potential for controlling the THz waves is still under evaluation. We are demonstrating the optical control of specific states of the germanium telluride (GeTe) PCM and its integration as a control element for enabling future optically reconfigurable THz devices. The excellent contrast of the material's THz properties in the two dissimilar states was used for optical-induced modulation of THz resonances of a metamaterial based on split-ring-resonator metallic structures integrating GeTe patterns. We experimentally confirm for the first time the feasibility of all dielectric GeTe-based THz polarizers, presenting broadband responses, high extinction ratios when the GeTe is in the metal-like phase, and almost transparency when amorphous. This highly functional approach based on optically controlled multioperational THz devices integrating PCMs is extremely stimulating for generating future disruptive developments (field-programmable metasurfaces, dielectric coding metamaterials) with multifunctional capabilities for THz waves manipulation.
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