  The problem of an electromagnetic wave scattering by a slab with two rough
boundaries is solved by a small-perturbation method under the Rayleigh
hypothesis. In order to obtain a perturbative development, we use a systematic
procedure which involves integral equations called the reduced Rayleigh
equations. Then we will show for a dielectric slab deposited on a silver film
that the backscattering enhancement can be produced by guided waves which
interact with the two rough surfaces.
