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

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 mu m for 135 degrees linearly polarized wave and dual-band absorptivity of 91.5% and 99.4% at 3.058 mu m and 3.887 mu m respectively for 45 degrees 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. (C) 2019 The Japan Society of Applied Physics