Omnidirectional absorption and off-resonance field enhancement in dielectric cylinders coated with graphene layers

We investigate electromagnetic scattering and absorption by dielectric cylinders coated with a concentric plasmonic shell at arbitrary incidence angles. Exploiting bulk and surface plasmon resonances in the long wavelength regime, we obtain an analytical condition to achieve wide-angle enhanced absorption for both TE and TM polarizations. By using the Lorenz -Mie theory, we apply this result to investigate electromagnetic absorption in a silicon cylinder coated with a graphene monolayer epitaxially grown on silicon carbide. Our theoretical results show that enhanced absorption occurs for a broad frequency range in the terahertz, and that omnidirectional absorption exists at a frequency in between the bulk and localized surface plasmon resonances. By showing that omnidirectional absorption does not correspond to an extinction resonance, we associate this phenomenon with off-resonance field enhancement in this system, which in turn is explained in terms of Fano resonances in the graphene layer. (C) 2015 Optical Society of America