Cooperative Emission of an Excited Monolayer into Surface Plasmons

The cooperative emission of an excited molecular monolayer into surface plasmons of a metallic substrate is described. The effect arises from the very strong coupling of an electronically excited molecule to surface plasmons at distances that are short compared to the wavelength of the electronic transition. Strong resonant enhancement of this excited molecule-surface plasmon interaction occurs for near-degeneracy of the electronic transition frequency and the asymptotic surface plasmon frequency ω
p
/2
^½
. It is shown theoretically how the two-dimensional analogue of superradiance can arise, leading to a highly directional and very intense surface plasmon pulse. This pulse or series of pulses has soliton-like characteristics and may be expected to propagate for considerably longer distances along the metal-vacuum interface than do individual surface plasmons.