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Numerical analysis of surface plasmons excited on a thin metal grating

The authors numerically investigated the characteristics of surface plasmons excited on a thin metal grating placed in planer or conical mounting. After formulating the problem, the solution method, Yasuura’s method (a modal expansion approach with least-squares boundary matching) was described. Although the grating is periodic in one direction, coupling between TE and TM waves occurs because arbitrary incidence is assumed. This requires the employment of both TE and TM vector modal functions in the analysis. Numerical computations showed: (1) the excitation of surface plasmons with total or partial absorption of incident light; (2) the resonance character of the coefficient of an evanescent order that couples the plasmon surface wave; (3) the field profile and Poynting’s vector. The plasmons excited on the surfaces of a thin metal grating are classified into three types: SISP, SRSP, and LRSP, different from each other in the feature of field profile and energy flow. In addition, the eigenvalue of a plasmon mode was obtained by solving a sequence of diffraction problems with complex-valued angles of incidence and using the quasi-Newton algorithm to predict the real angle of incidence at which the absorption occurs.