Colossal terahertz field enhancement using sub-10 nm gap split ring resonator

Abstract

Resonant terahertz (THz) antennas have been a versatile tool for nonlinear THz science and application such as high sensitivity THz sensing through its strong local field enhancement. Here, we demonstrate nanometer-sized gap split ring resonators (SRRs), which can focus terahertz waves up to tens of thousands times at magnetic resonance frequency. An array of sub-10 nm gap split ring resonators was fabricated with high-throughput, simply by repeating standard photolithography, argon ion milling, and atomic layer deposition (ALD). To experimentally study the terahertz response of nanogap split ring resonators, we performed far-field THz-time domain spectroscopy (TDS). In addition, the transmission properties, charge distribution, and electric field enhancement are numerically investigated. By combining those experimental and numerical results, we confirm its colossal electric field enhancement factor reaching up to ~36000 with the resonance frequency at ~0.25 THz. The resonance structure of SRRs enables us to increase field enhancement by an order of magnitude compared to the slit structure with the same width.