Selective and Tunable\nAbsorption of Twisted Light\nin Achiral and Chiral Plasmonic Metasurfaces

The symmetry of achiral metasurfaces suggests selective\nabsorption\nis nonexistent when irradiated either by circularly polarized Gaussian\nor twisted light beams carrying orbital angular momentum (OAM). In\nchiral metasurfaces, the lack of symmetry leads to differential absorption\nwhen probed with chiral light either in the form of circular polarization\n(circular dichroism) or helical phase fronts (helical dichroism).\nHere, we demonstrate differential absorption of asymmetric twisted\nlight beams, known as helical dichroism, which exist in an array and\na single achiral structure and can be controlled. When extended to\nchiral structures, these asymmetrical chiral light modes enable to\nenhance and tune chiroptical sensitivity. Our technique offers more\ncontrol parameters than just changing the OAM value, as presented\nin previous studies. Selective response to asymmetric helical light\nbeams is qualitatively explained in terms of induced multipole moments.\nThe presence of dichroism in achiral nanostructures offers a significant\nfabrication advantage over complex chiral structures and enables the\ndevelopment of next-generation plasmonic-based chiroptical spectroscopy\nand molecular sensing.