Diffraction characteristics of metallic reflection gratings

Plane-wave diffraction by metallic reflection gratings with finite conductivity of arbitrary profile is analysed by a new analytical-numerical technique. The obliquely incident radiation is of linear polarisation with either of its fields parallel to the rulings. The solution method is simple, general and numerically efficient. It involves expansion by a Fourier series of the periodic permittivity function in the inhomogeneous grating region, and application of finite differences to numerically solve the inhomogeneous vector-wave equation in this region. Numerical results are presented for several gratings to demonstrate the convergence, reliability and accuracy of the method. They also show effect of the finite conductivity of metal on the diffraction characteristic of gratings.