Diffraction at a two-dimensional periodic plasmon grating of finite dimensions

Numerical-analytical methods, algorithms, and programs developed for two-dimensional periodic diffraction gratings (DG) have been used. It is assumed that the current distributions on the quasi-periodic (limited in size, but with a large number of elements) DG is the same as on the periodic DG. Using the Poisson transform, the radiation pattern of the quasi-periodic DG has been found. The radiation patterns of multilayer DG made of plasmon rectangular strips (grapheme strips in the terahertz range and metal strips in the optical range) have been studied. The approximate Kubo boundary conditions for graphene and the complex permittivity of metals in the optical range have been used.