Coherent and Incoherent Radiation from Optically Excited Surface Plasmons on a Metal Grating

Excitation of surface charge waves (surface plasmons) produces intensity anomalies in the light reflected from a metal grating. We demonstrate that coupling occurs for both s- and p-polarized light if the grating lines are oblique to the plane of incidence, provided there is a component of the incident electric field along the direction of surface-wave propagation. We have measured the magnitude, phase, and direction of the plasmon electric field, and find Fano's theory confirmed. Underlying the coherent radiation we observe a small incoherent component resulting from spontaneous emission by the surface plasmons.