Confinement of enhance-transmitted light beam by surface plasma induced on sub-wavelength slits.*

The enhancement of light transmission through sub-wavelength slit is an interesting and important recent discovery in plasmonic nano-photonics. This is studied with our newly developed two dimensional simulation code of finite-difference time-domain method.~The simulations verify the enhanced transmission that far exceeds the diffraction limit and help to understand in depth the resultant beaming of light that will be important in nano-optical applications. The beaming of light is found due to the interference of the first order scattered light with the zeroth order transmitted light and is divergent with a finite angle. By proposing the interference between the zeroth and zeroth orders, we found the light can be confined as an almost divergence-less beam. The dynamics and interesting physics of our new scheme and founding will be discussed.