SCATTERING OF LIGHT FROM A THIN METALLIC FILM WITH A SHALLOW RANDOM ROUGH-SURFACE BETWEEN DISSIMILAR MEDIA .1. THEORY

The reflected field scattered from a thin metallic film with a shallow rough random surface bounded by two semi-infinite dissimilar optical media is calculated. The model assumes that all media are homogeneous, isotropic, non-magnetic, linear and may be characterized by a frequen cy dependent complex dielectric function. The Rayleigh hypothesis is u sed to obtain an independent integral equation relating the amplitudes of the reflected fields to the incident wave. This treatment is valid for both TM(p) or TE(s) polarizations. Numerical results are obtained by assuming a Gaussian roughness spectrum for the random rough surfac e and the formalism is applied to simulate the scattering in the ATR-K retschmann configuration, allowing the excitation of surface plasmons (SP), prism-metal-air. The angular dependence of the incoherent scatte ring shows two enhancement peaks, in addition to the well known backsc attering effect. The angular positions of these two peaks are about th e angle of excitation of SP (+/- theta(sp)) and are independent of the angle of incidence theta(i). They appear only for p-polarized light a nd are due to single-scattering effects. When theta(i) is tuned at exa ctly -theta(sp) the enhanced backscattering peak is screened by the pe ak located at this angle and the background incoherent scattering is t wo orders of magnitude higher for the same response computed for all o ther angles of incidence theta(i). (C) 1997 Elsevier Science B.V.