The on and off of optical waves in planar metal/dielectric stacks

Diffraction is a universal characteristic of optical waves. It sets a resolution limit to optical imaging instruments and limits the size of laser beams with diffraction spreading. Now remarkable progress to beat diffraction limit has been made, including stimulated emission depletion (STED), stochastic optical reconstruction microscopy (STORM), near field imaging, NIM for perfect image, etc. However, the use of Surface Plasmon Resonance to beat diffraction has never been conceived. Here, for the first time, we show that coupling SPPs to appropriate dielectric material in planar multilayer stacks can result in a fundamentally down-sized laser beam without diffraction spreading.The plasma polaritons stops at the dielectric interface, and electromagnetic oscillations keep going in the coupling dielectric medium as a new light emission. This study will open up a new route for sub-wavelength-sized nano-laser beaming technology.