2023 Spring Graduate Colloquium Series: Sanjib Thapa
Gold nanolens for chiral single molecule spectroscopy
The angular momentum of light has two independent components-spin angular momentum (SAM) and orbital angular momentum (OAM). The mechanism of the SAM of light-matter interaction and the chiral molecule discrimination has been described in many papers. However, the mechanism of OAM of light-matter interaction is not easy to perceive. With the development of nanotechnologies, transfer of OAM of light to a single molecule is becoming a hot topic. The development of nanolens for light with OAM is crucial to study the molecular chirality. Here, manufacturable nanolens is proposed which can efficiently focus light with OAM onto the nanoscale, and create the plasmonic vortex, which is much smaller than the diffraction limited vortex focused by an ordinary lens. The generated plasmonic vortex can differentiate the chirality and can also probe electronic dipole-forbidden transitions. The optimized design of the nanolens consists of several radially aligned rods that is easy to manufacture for the visible wavelengths range. Here, it is proved that nanolens can work with both even and odd number of rods and, shown the minimum number of rods needed to design the nanolens. Eventually, the efficiency of the nanolens for both left- and right-handed light has been studied.
Keywords: nanoantenna, OAM, optical vortex