Polarization-controlled triple-band absorption in all-metal nanostructures with magnetic dipoles and anapole responses

Abstract

An all-metal absorber consisting of an L-shaped stripe with two vertical pillars is constructed and investigated for triple-band absorption. The nanostructure reveals distinct absorption properties at resonant wavelengths selected by the polarization of incident waves. It achieves single-band absorptivity of 98.5% at 5.198 μm for 135° linearly polarized wave and dual-band absorptivity of 91.5% and 99.4% at 3.058 μm and 3.887 μm respectively for 45° linear polarization. We interpret the physical mechanism by using the charge-current multipolar expansion framework, which shows that the excitation of two transverse magnetic dipoles and a non-radiating anapole are responsible for these absorption resonances.