Nanofocusing of optical vortex in plasmonic structures

Optical vortex or orbital angular momentum (OAM) of light are a subject of active research and have been employed for novel applications such as optical manipulation, quantum information and control of cold atoms [1]. For decades, it has been discussed if OAM of light could affect the state of a bound system of charges such as an atom or a molecule, an exchange should arise between light and matter, especially in a transition between the energy levels [2-4]. In order to realize such an OAM exchange between light and matter, it is inportant to macth the wavefunction of light and a bound system, either by squeezing a distribution of light or expand the wavefunction of a bound system. Here we numerically demonstrate a scheme to squeeze a distribution of light with OAM into nanoscale. A transfer of OAM from photon to surface plasmon resonance (SPR) [5], is exploited for this nanofocusing.