Gold nanolens for chiral single molecule spectroscopy

Abstract High demand for techniques to study molecular chirality inspires us to develop a nanolens for light with orbital angular momentum (OAM). The proposed nanolens can efficiently focus light with OAM onto the nanoscale, and create a so-called plasmonic vortex, which is much smaller than the diffraction limited vortex focused by an ordinary lens. The generated plasmonic vortex can efficiently differentiate between left- and right-handed molecules and probe electronic dipole-forbidden transitions. The nanolens consists of several radially aligned rods, and exploits surface plasmons to generate a plasmonic vortex-like structure in the center. We optimize this design to be suitable for beams with various topological charges, and to be easy to manufacture for the visible wavelengths range. We prove that nanolens can work efficiently with both even and odd number of rods. We study the efficiency of the nanolens for both left- and right-handed light, and show the resultant electric field and phase distributions.