Generation of plasmon modes in a supernarrow nanoslit formed by silver surfaces

We report a theoretical study of plasmon generation of a giant electromagnetic field in a supernarrow nanoslit formed by a silver cylinder and a flat mirror surface. It is shown that as the silver surfaces approach each other, gap plasmons are excited in the gap between them, which results in a resonant amplification of the field. It is demonstrated for the first time that the electric field amplification increases with decreasing distance between the cylindrical and flat surfaces and reaches saturation, at which the field intensity becomes record high, exceeding the incident wave intensity by ten orders of magnitude. The found gap plasmon modes will increase the sensitivity to the detection of small concentrations of molecules, down to single molecules, by the methods of giant Raman scattering of light and plasmon-enhanced IR spectroscopy.