Terahertz field confinement and enhancement in various sub-wavelength structures

Terahertz plasmonics is one of the fascinating research fields that includes diverse applications in nonlinear terahertz optics and nano-optics, as well as studies about strong localization and enhancement of millimeter waves. Recent advanced lithography techniques enable one to reach the confinement scale of electromagnetic waves down to subnanometer, which corresponds to wavelength/10 000 000. In particular, the strong electric-field enhancement in metal gaps can produce atomically strong field exceeding similar to 10 MV/cm in a picosecond time scale. In this article, we review the strong localization and enhancement of electromagnetic waves in terahertz frequency ranges achieved by subwavelength metal structures. Based on understanding the underlying capacitive coupling and antenna effects, we focus on the field confinement and enhancement of various metal structures such as slit, slot antenna, and dipole antenna. We also give a brief introduction about near-field detection methods.