Sub-diffraction thin-film sensing with planar terahertz metamaterials

TL;DR

This paper demonstrates a terahertz near-field sensing approach using planar metamaterials to detect ultra-thin dielectric films with minimal area, significantly enhancing resonance quality and enabling biomolecular detection.

Contribution

The study introduces a near-field terahertz sensing method that reduces the sensing area and improves resonance Q factor by positioning the metamaterial close to the sub-diffraction terahertz source.

Findings

Resonance Q factor increased by 113%.

Minimal sensing area achieved as small as 0.2λ x 0.2λ.

Effective detection of films with thickness λ/375.

Abstract

Planar metamaterials have been recently proposed for thin dielectric film sensing in the terahertz frequency range. Although the thickness of the dielectric film can be very small compared with the wavelength, the required area of sensed material is still determined by the diffraction-limited spot size of the terahertz beam excitation. In this article, terahertz near-field sensing is utilized to reduce the spot size. By positioning the metamaterial sensing platform close to the sub-diffraction terahertz source, the number of excited resonators, and hence minimal film area, are significantly reduced. As an additional advantage, a reduction in the number of excited resonators decreases the inter-cell coupling strength, and consequently the resonance Q factor is remarkably increased. The experimental results show that the resonance Q factor is improved by 113%. Moreover, for a film with a thickness of \lambda/375 the minimal area can be as small as 0.2\lambda by 0.2\lambda. The success of this work provides a platform for future metamaterial-based sensors for biomolecular detection.