Super-radiance near conducting and plasma surfaces

It is noted that in free space, an excited atom undergoing an electric dipole transition can decay at twice the normal rate when a second, ground-state atom is present in its vicinity. Full expressions are obtained for the decay rates of a two-atom system in the presence of metallic surfaces which are either conducting or approximately represented by an electron plasma model. The quantized transverse vector potential in the presence of an infinite conducting surface is defined, and it is shown how this leads to the decay-rate expression for a single excited atom at a fixed distance from the surface. Two-atom systems near a perfect conductor and a plasma surface are considered, three different dipole configurations are examined for the perfect-conductor case, and one configuration is analyzed for the plasma-surface case. The results indicate that: (1) an excited atom near a conducting surface can have a lifetime four times shorter than the normal one when a similar, ground-state atom is placed close to it; (2) other important contributions are made by surface plasmons, which are also enhanced in the presence of the resonating atom; and (3) the surface-plasmon contributions are exponential functions of distance from the surface and are, therefore, significant only close to the surface.