We report on the observation of terahertz transparency in random arrays of the single rectangular holes and slits with the areal coverage of only 12%. The terahertz transparency occurs at the fundamental shape resonance of the rectangular holes and confirms the theoretical predictions of earlier works of García-Vidal et al. [ Phys. Rev. Lett. 95, 103901 (2005)] on single rectangular holes and of Ruan and Qiu [ Phys. Rev. Lett. 96, 233901 (2006)] on random arrays of holes.

We report that vanadium dioxide films patterned with λ/100000 nanogaps exhibit an anomalous transition behavior at millimeter wavelengths. Most of the hybrid structure’s switching actions occur well below the insulator to metal transition temperature, starting from 25 °C, so that the hysteresis curves completely separate themselves from their bare film counterparts. It is found that thermally excited intrinsic carriers are responsible for this behavior by introducing enough loss in the context of the radically modified electromagnetic environment in the vicinity of the nanogaps. This phenomenon newly extends the versatility of insulator to metal transition devices to encompass their semiconductor properties.

We present 2D measurements of the full THz electric field behind a sample consisting of multiple slits in a metal foil. Our measurements, which have a sub-wavelength spatial, and a sub-period temporal resolution, reveal electric field lines, electric field vortices and saddle points. From our measurements we are able to reconstruct the magnetic field and, finally, the position and time-dependent Poynting vector which shows the flow of energy behind the sample. Our results show that it is possible to study the flow of light near sub-wavelength plasmonic structures such as slit-arrays and, by implication, other metamaterial samples.

Understanding light interaction with metallic structures provides opportunities of manipulation of light, and is at the core of various research areas including terahertz (THz) optics from which diverse applications are now emerging. For instance, THz waves take full advantage of the interaction to have strong field enhancement that compensates their relatively low photon energy. As the THz field enhancement have boosted THz nonlinear studies and relevant applications, further understanding of light interaction with metallic structures is essential for advanced manipulation of light that will bring about subsequent development of THz optics. In this review, we discuss THz wave interaction with deep sub‐wavelength nano structures. With focusing on the THz field enhancement by nano structures, we review fundamentals of giant field enhancement that emerges from non‐resonant and resonant interactions of THz waves with nano structures in both sub‐ and super‐ skin‐depth thicknesses. From that, we introduce surprisingly simple description of the field enhancement valid over many orders of magnitudes of conductivity of metal as well as many orders of magnitudes of the metal thickness. We also discuss THz interaction with structures in angstrom scale, by reviewing plasmonic quantum effect and electron tunneling with consequent nonlinear behaviors. Finally, as applications of THz interaction with nano structures, we introduce new types of THz molecule sensors, exhibiting ultrasensitive and highly selective functionalities.