SPECKLE PATTERN INTENSIFICATION IN HIGHLY CONDUCTING MICROROUGH GRATINGS

The scattering of a plane wave by a rough interface between a vacuum and a metal is computed for the case of a boundary constructed as the sum of two contributions: a perfectly periodic sinusoidal roughness representing an ideal grating and a statistically varying roughness representing the defects of a real diffraction grating. We restrict ourselves to the case of highly conducting shallow gratings, so that Rayleigh expansions and a surface impedance boundary condition can be used as an approximation. The speckle patterns obtained for p-polarized light show intensification at angular positions that do not depend on the incidence. We show that the presence of surface plasmons propagating on the grating is related to this intensification.