Toroidal dipole resonances enable giant vortical dichroism in folded metamaterials

Chiral optical effects have significant applications in material science and nanophotonics, particularly in chiral material detection and optical sensing. The toroidal dipole resonance, as a unique electromagnetic multipolar mode, has attracted considerable attention for its distinctive response characteristics in optical research. In this work, we propose a folded metamaterial and investigate the interaction between photonic orbital angular momentum and the toroidal dipole resonances in the designed chiral metamaterials. By varying the folded angle of the metamaterial, we analyze the variations in vortical dichroism response and find that the folded angle significantly affects the intensity and contrast of the vortical dichroism effect. By using electromagnetic multipole resonances theory, we verify that the vortical dichroism enhancement is mainly driven by toroidal dipole resonance intensity and confirm chiral toroidal dipole resonances in the orbital angular momentum dimension. This study provides what we believe to be a new pathway for flexible orbital angular momentum manipulation and the development of chiral toroidal dipole optical devices, especially in optical communications and optical holography applications.