Eliminating the Rayleigh anomalies in metal grating

We demonstrate that Rayleigh anomalies of some diffraction order of metal reflection gratings and transmission grating can be eliminated. The studied grating consists of a one-dimensional (1-D) periodic rectangular slit array. A systemic rule has been reported that can be used to counteract the infinity of the Green function resulted from working at the Rayleigh cutoff wavelength, by choosing a suitable value of the ratio of the slit width to the period of the grating. Eliminating the Rayleigh anomalies is of intrinsic physical interest as well as of vital concern in the design of the optical element.