Directional and singular surface plasmon generation in chiral and achiral nanostructures demonstrated by Leakage Radiation Microscopy

TL;DR

This paper demonstrates how leakage radiation microscopy can be used to analyze and quantify the directional and vortex generation of surface plasmon polaritons in chiral and achiral nanostructures, supported by an analytical model.

Contribution

It introduces a new method for probing plasmonic chirality and directionality using leakage radiation microscopy combined with an analytical model for understanding spin-orbit interactions.

Findings

Successful experimental demonstration of spin-driven directional coupling.

Quantitative measurements of directivity and extinction ratios.

Analytical model explaining directionality and vortex formation.

Abstract

In this paper, we describe the implementation of leakage radiation microscopy (LRM) to probe the chirality of plasmonic nanostructures. We demonstrate experimentally spin-driven directional coupling as well as vortex generation of surface plasmon polaritons (SPPs) by nanostructures built with T-shaped and $\Lambda$- shaped apertures. Using this far-field method, quantitative inspections, including directivity and extinction ratio measurements, are achieved via polarization analysis in both image and Fourier planes. To support our experimental findings, we develop an analytical model based on a multidipolar representation of $\Lambda$- and T-shaped aperture plasmonic coupler allowing a theoretical explanation of both directionality and singular SPP formation. Furthermore, the roles of symmetry breaking and phases are emphasized in this work. This quantitative characterization of spin-orbit interactions paves the way for developing new directional couplers for subwavelength routing.