Generation of surface optical screw dislocations by evanescent plasmonic modes

A novel form of optical screw dislocation based on localized surface-plasmon modes (SPMs) is described. In particular, we show that a metallic sheet in the form an infinitesimally thin film deposited on a planar dielectric substrate creates surface-plasmon modes due to evanescent Laguerre-Gaussian (LG) light. The characteristic property of such a mode is the exponential decay with distance normal to the interface in the vacuum region. This localized mode can be described as a surface optical screw dislocation possessing a desirable enhancement due to the localized surface plasmon content of the mode. Such a screw dislocation is controllable by changing the angle of internal reflection and the quantum numbers of the LG light.