Beaming effect of optical near-field in multiple metallic slits with nanometric linewidth and micrometer pitch

The beaming effect and interference patterns on the exit surface of multiple nano metallic slits with micrometer pitch were observed by scanning near-field optical microscopy. The near-field light intensity for multiple slits had a longer propagation tail and a smaller diverging angle as compared to that in a single slit. From finite-difference time-domain calculations, we verify that these fringe patterns come from the interference effect of longitudinal electric field, which is propagating along the surface. The beaming light in the slit openings is also attributed to the addition of longitudinal fields.