Local THz resonances in semiconductors: Active control of near-fields, THz extinction and beaming

The versatile nature of semiconductors with a permittivity that can be controlled by the amount of free carriers, makes them excellent materials for active plasmonics and metasurfaces. Structures made out of semiconductors can give rise to localized resonances at THz frequencies. The precise behavior of these structures depends on their geometry and permittivity; parameters that can be actively tuned. Subwavelength local field enhancements are the most relevant characteristic of localized resonances. These enhancements have triggered the interest for resonant metallic structures in sensing and spectroscopic applications. Local field enhancements in plasmonic structures have been thoroughly investigated at optical and infrared frequencies using near field probing techniques [1]. These techniques provide an excellent spatial resolution but they are not sensitive to the individual field components.