Dual-band Near-Perfect Optical Absorption by Graphene-Coated Core-Shell Spherical Nanoparticles

In this paper, a dual-band optical absorber is designed using graphene-coated core-shell nanoparticles. The performance of the proposed structure is based on the excitation of localized surface plasmon resonances (LSPRs) in the dual graphene sheets wrapped around the core and shell. Since the excited LSPRs are in the deep sub-wavelength regime, each core-shell sphere can be considered as a polarizable particle in the quasi-static regime and it exhibits high absorptivity when arranged in a periodic lattice. By proper choice of the geometrical, optical, and material properties, it is feasible to reach complete optical absorption in the dual operating bands after residing the patterned particles on top of a reflecting mirror. Due to the spherical symmetry, the proposed absorber is not sensitive to the incident angles of transverse electric (TE) and transverse magnetic (TM) waves up to around 55° in both frequencies.