Excitation of surface plasmons by finite width beams.

The field properties of surface plasmons produced by realistically bounded beams incident in various attenuated total reflection (ATR) geometries are examined. Analytical results are first derived for the general case dealing with a beam field incident in a multilayered configuration. We show that, at the phase matching condition, the reflected field can be severely distorted in comparison with the incident beam shape. We also find that the power intensity inside the metal medium can be much smaller than that expected under the assumption of plane wave incidence. However, when the beamwidth is larger than the proportion range of the excited plasmon, the power intensity profiles and find that they exhibit distinguishing characteristics. In particular, for an incident Gaussian beam, the location of maximum power density on the metal surface shifts with respect to the center of the incident beam by a distance of the order of the plasmon propagation length. For a rectangular beam incident at the phase matching condition, on the other hand, the propagation range of the coupled surface plasmon can be found directly from the profile of the reflected field. We also show the overall process of beam wave coupling in the ATR geometry can be simulated by a spatial operating system having the response of either a differentiator (for the reflected field) or an integrator (for the transmitted field).