Narrow band perfect absorber for maximum localized magnetic and electric field enhancement and sensing applications

TL;DR

This paper introduces an all-metal plasmonic absorber with ultra-narrow bandwidth and high absorption efficiency, enabling maximum localized electromagnetic field enhancement and high-sensitivity sensing applications.

Contribution

It presents a novel design for a narrowband perfect absorber based on vertical gap plasmonic modes, achieving high quality factor and mode volume, surpassing traditional configurations.

Findings

Absorption bandwidth less than 8nm with over 99% absorptivity.

Field enhancement proportional to absorption, enabling maximum enhancement at perfect absorption.

Refractive index sensor with sensitivity 885nm/RIU and FOM of 110.

Abstract

Plasmonics offer an exciting way to mediate the interaction between light and matter, allowing strong field enhancement and confinement, large absorption and scattering at resonance. However, simultaneous realization of ultra-narrow band perfect absorption and electromagnetic field enhancement is challenging due to the intrinsic high optical losses and radiative damping in metals. Here, we propose an all-metal plasmonic absorber with an absorption bandwidth less than 8nm and polarization insensitive absorptivity exceeding 99%. Unlike traditional Metal-Dielectric-Metal configurations, we demonstrate that the narrowband perfect absorption and field enhancement are ascribed to the vertical gap plasmonic mode in the deep subwavelength scale, which has a high quality factor of 120 and mode volume of about 10^-4*({\lambda}/n)^3 . Based on the coupled mode theory, we verify that the diluted field enhancement is proportional to the absorption, and thus perfect absorption is critical to maximum field enhancement. In addition, the proposed perfect absorber can be operated as a refractive index sensor with a sensitivity of 885nm/RIU and figure of merit as high as 110. It provides a new design strategy for narrow band perfect absorption and local field enhancement, and has potential applications in biosensors, filters and nonlinear optics.