We investigate the scattering properties of a metal surface composed of the sum of a sinusoidal component and a one-dimensional Gaussian random process. In experimental work, such surfaces are produced in gold-coated photoresist by combining speckle-scanning methods with holographic grating fabrication techniques. In the diffusely scattered light, light bands and related effects that arise from the excitation of surface plasmon polaritons are observed; the angular position of the diffuse light bands corresponds to the positions of the resonant absorption anomalies of the unperturbed periodic surface. It is also shown that the measurements are closely consistent with the predictions of rigorous numerical methods based on the reduced Rayleigh equations, in which the diffuse scatter is determined through an average over an ensemble of rough surfaces. With an analytical theoretical method that treats the grating exactly and the roughness as a perturbation, it is shown that an observed enhancement of a diffuse light band in the backscattering configuration results from the coherent interference of scattering contributions from counterpropagating surface plasmon polaritons.
© 1995 Optical Society of America
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