Dipole radiation in the presence of a rough surface. Conversion of a surface-polariton field into radiation

The characteristics of the radiation produced by a dipole, located near the rough surface of a material medium, are examined. The field distribution is calculated at any point outside the medium for arbitrary orientation of the dipole moment, so that one may obtain the electromagnetic Green's function in the presence of surface roughness. The medium can have either local or a nonlocal dielectric function and the results are valid to first order in roughness. The surface roughness converts the surface polariton field, created even in the absence of roughness, into radiation and thus leads to well-defined resonances in the farfield radiation pattern. Numerical results for the case of metallic as well as dielectric gratings are given. The effect of the nonlocality of the dielectric function on the resonances in the radiation is shown to be significant in certain cases. For metallic gratings the dominant effect of the nonlocality is to shift the position of the angular resonances.