Photo-acoustic detection of chirality in metal-polystyrene metasurfaces

Nowadays, nanophotonics aims towards low-cost chip-scale devices that can tailor electromagnetic properties, one of which is the control of circular polarization at the nanoscale. Here, we demonstrate the chiral properties of metasurfaces produced by means of nanosphere lithography combined with tilted metal deposition. We apply the photo-acoustic technique to characterize the circular dichroism (CD) at 633 nm of polystyrene nanospheres covered by three different metals: Au- and Cr-covered samples show extrinsic chiral behavior, while the Ag-covered sample shows CD at normal incidence, characteristic of intrinsic chirality. As the experimental data are in good agreement with numerical predictions, we believe that such design can be optimized to get efficient circularly polarized detection at the nanoscale