PHOTON-SURFACE-PLASMON COUPLING IN THICK AG FOILS

Photon-surface-plasmon coupling is observed in measurements of the optical reflectance of thick vapor-deposited Ag foils. Measurements of the surface-plasmon wave vector demonstrate that the optical excitation of the mode is an indirect process, the coupling mechanism providing the majority of the surface-plasmon momentum. Several experiments are performed in order to distinguish between various possible mechanisms, and only the surface roughness of the foil is found to contribute significantly to the observed interaction. The real and imaginary parts of the frequency-dependent dielectric response function are computed from the ellipsometry data of several foils. The surface-plasmon contribution appears as a resonant excess absorption in the imaginary part of the response, rising as much as 50% above the background level in the cases considered. The response of one foil is computed from data taken at two different angles of incidence in an attempt to observe the nonlocal nature of the portion of the absorption due to the surface-plasmon mode. © 1969 The American Physical Society.