Strong Chiral Response of Chiral Plasmonic Nanoparticles to Photonic Orbital Angular Momentum

Chiral plasmonic nanomaterials have been widely utilized to study light-matter interactions due to its capability to amplify chiroptic signals. Conventionally, chiro-optic experiments have demonstrated interactions between circularly polarized light and materials. However, employing light with chiral phase, i.e., optical vortex, can generate a strong chiral response and holds the potential to unveil extensive material information owing to the infinite topological numbers. In this work, an array of 3D chiral nanoparticles is employed to demonstrate large helical dichroism (HD). Chiral gold nanoparticle arrays are illuminated by vortex beams of opposite helicity, which revealed the high HD value of 0.93. The chiral interaction is theoretically investigated, and enantioselective interaction can be explained by multipole analysis. It is determined that the strong HD is attributed to the interaction of higher-order multipole moments such as electric quadrupole and magnetic quadrupole moments. This study provides deeper insight into understanding of the interaction between optical vortex and chiral plasmonic nanostructures and paves the way for next-generation chiroptical applications ranging from ultrasensitive chiral spectroscopy to chiral quantum optics.