Optical field enhancement and tunneling phenomena in nanogaps

Abstract

In this thesis, I studied strong light-matter interaction in vertically aligned metal-insulator-metal nanogaps. Prepared nanogaps were evaluated by optical transmission measurement, exploiting Kirchhoff integral formalism and interferometric method. The measured optical field enhancements were in the order of ~ 10 and showed Fabry-Pérot resonance behavior coming from the waveguide mode of the nanogap. Due to the strong coupling between light field and metallic nanogaps, the transmitted light or photoluminescence of metal were greatly enhanced. For the field strength across the gap over ~ 1 V/nm regime, quantum tunneling process emerges, and it greatly modifies the optical response of the nanogaps. I measured and quantified the electromagnetically-driven ultrafast tunneling current using conventional electronics, exploiting the macroscopic symmetry of the closed ring barrier. Strong THz pulse was fully-rectified in the ring, and the spatiotemporal dynamics of the THz current was experimentally visualized by the optical probe method. This work will lead to the ultrafast optoelectronics, THz multiplexing, ultra-high bandwidth communications and wireless energy transfer technique.