Effect of defect depth on surface plasmon scattering by subwavelength surface defects

Surface plasmon scattering by bidimensional indentations and protrusions is examined, mainly in the optical regime. The width of the defects is fixed, while their height is varied. Both individual defects and arrays of defects are considered. Protrusions mainly reflect the incident plasmons in the optical range. Indentations mainly radiate the incident plasmon out of plane. An indentation produces maximum reflection and out-of-plane radiation at the same wavelength when its interaction with the incident surface plasmon is resonant. Protrusions, in general, exhibit maximum reflection and radiation at different wavelengths. Shallow arrays of either defects produce a photonic band gap, whose spectral width can be broadened by increasing the defects height or depth. At wavelengths inside the band gap, ridge arrays reflect surface plasmon polaritons (SPP’s) better than groove arrays while groove arrays radiate SPP’s better than ridge arrays.