K gaps for surface polaritons on gratings : excitation by fast electrons

We have derived the equations for light emission due to fast particles impinging on a metallic grating. We have solved these equations numerically to study the emission peaks due to the decay of surface polaritons (SPO's) on a Ag grating bombarded by 80-keV electrons. The SPO dispersion curve can be inferred from these peaks. Our calculations reproduce the anomalous behavior ({ital k} gap) of the SPO dispersion curve that was observed by Heitmann {ital et} {ital al}. near the 2{pi}/{ital a} Brillouin zone boundary, {ital a} being the period of the grating.