Extrinsic chirality in metasurfaces: Traditional and unconventional experiments – INVITED

Department S.B.A.I., Sapienza University of Rome, Via A. Scarpa 14, I-00161 Rome, Italy

^* Corresponding author: emilija.petronijevic@uniroma1.it

Published online: 18 October 2023

Abstract

Plasmonic nanostructures with achiral, but asymmetric shapes can exhibit chiro-optical phenomena at the nanoscale, given that the nanostructure-light interaction symmetry is broken. Such behaviour is defined as extrinsic chirality, and it is induced by properly arranging the experimental set-up. We show measurement techniques for extrinsic chirality in low-cost, asymmetric samples with nanostructures organized in metasurfaces. We employ widely tuneable chiro-optical characterization of transmission and reflection, as well as the circular polarization degree of the transmitted signal; near-infrared range (680-1080nm) and oblique incidence allow for the detection of resonant features in extrinsic chirality. Other, unconventional experiments use photo-thermal consequences of chirality governed absorption in metasurfaces. Photo-acoustic spectroscopy directly gives circular dichroism as a differential absorption of the left and right circular polarizations exciting the sample. Photo-deflection spectroscopy gives additional information of diffraction phenomena governed by the extrinsic chirality. We showed that these techniques can monitor the extrinsic chiral behaviour of the hybrid plasmonic metamaterials. Moreover, they can be used in combination with fluorescence-detected circular dichroism to measure the emission properties of fluorescent materials.