Anomalous extinction in index-matched terahertz nanogaps

Author:

Jeong Jeeyoon1,Kim Dasom1,Park Hyeong-Ryeol2,Kang Taehee1,Lee Dukhyung1,Kim Sunghwan1,Bahk Young-Mi1,Kim Dai-Sik1

Affiliation:

1. Department of Physics and Astronomy and Center for Atom Scale Electromagnetism, Seoul National University, Seoul 08826, Korea

2. Department of Physics, Chungbuk National University, Chungbuk 28644, Korea

Abstract

AbstractSlot-type nanogaps have been widely utilized in transmission geometry because of their advantages of exclusive light funneling and exact quantification of near-field enhancement at the gap. For further application of the nanogaps in electromagnetic interactions with various target materials, complementary studies on both transmission and reflection properties of the nanogaps are necessary. Here, we observe an anomalous extinction of terahertz waves interacting with rectangular ring-shaped sub-30 nm wide gaps. Substrate works as an index matching layer for the nanogaps, leading to a stronger field enhancement and increased nonlinearity at the gap under substrate-side illumination. This effect is expressed in reflection as a larger dip at the resonance, caused by destructive interference of the diffracted field from the gap with the reflected beam from the metal. The resulting extinction at the resonance is larger than 60% of the incident power, even without any absorbing material in the whole nanogap structure. The extinction even decreases in the presence of an absorbing medium on top of the nanogaps, suggesting that transmission and reflection from nanogaps might not necessarily represent the absorption of the whole structure.

Publisher

Walter de Gruyter GmbH

Subject

Electrical and Electronic Engineering,Atomic and Molecular Physics, and Optics,Electronic, Optical and Magnetic Materials,Biotechnology

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