Fringe fields in nonlinear photoemission microscopy

Self-organized Ag nanostructures have been investigated by photoemission electron microscopy where the electrons are generated by femtosecond laser pulses through a two-photon photoemission process. Bright and dark areas are observed around the nanostructures when they exceed a certain lateral dimension. The features are different for both directions of the polarization of the incoming light and s and p polarization. In p polarization the features consist of several interference fringes that are explained by diffraction. The photoemission yield of Ag nanowires also shows a dependence on the polarization direction of the incoming light with respect to the orientation of the nanowire. This is explained with a particle plasmon state in the Ag nanostructures that acts as the intermediate state for two-photon photoemission. Also, we present evidence of far-field mediating interaction between neighboring Ag nanostructures.