Multipole terahertz localized plasmon resonances on spiral structures

Numerical simulations of sub-wavelength single and double logarithmic spiral metal disk array in the range of $0.04-5$ THz have shown that high order localized surface plasmon resonances arise at oblique incidence and small gap sizes between the disks. The spectra and 2D distributions of the EM field at the resonant frequencies depend on the geometry of the structure, period of the array, and a gap between the disks in the doubled spiral structures, but there is no dependence on the twisting direction of the spirals.