Giant-enhancement of extraordinary optical transmission through nanohole arrays blocked by plasmonic gold mushroom caps

An improved plasmonic hole array nanostructure model with the holes blocked by gold mushroom caps is proposed and it can realize a giant transmission with efficiency up to 65%, 182% larger than the unblocked nanohole array, due to the strong coupling between caps and holes, which plays the role of a cavity antenna. Moreover, the numerical investigation confirms that it provides more consistency with the practical experimental situations, than the nanodisk model instead. As expected, the light transmission sensitively depends on the geometric parameters of this new nanostructure; as the cap-hole׳s gap or cap׳s diameter vary, there always exists an optimal transmission efficiency. More interesting is that the corresponding optimal wavelength decreases with the gap׳s increment or the diameter׳s decrement, particularly in an exponential decaying way, and the decay rate is obviously influenced by the cap׳s parameters.