Large Circular Dichroism and Polarization Rotation in Plasmonic Ψ-Like Structured Gold Metasurface

A novel Ψ-like chiral plasmonic metasurface is designed and studied numerically using finite difference time domain (FDTD) computation to achieve large circular dichroism (CD) in the near-infrared (NIR) regime. The structure shows a distinct CD peak at 1110 nm with CD strength of ~ 0.65 and full width at half maxima (FWHM) of ~ 85 nm. The chiroptical response critically depends on the structural thickness (h) and inner radius (r_i). At low thickness (h < 100 nm), CD is observed to be very weak, although, a considerable CD appears at h ≥ 200 nm. On the other hand, a change in the inner radius by 100 nm shifts CD peak wavelength by ~ 200 nm. Giant CD arises due to high reflection damping at LCP (left circularly polarized) light excitation compared to RCP (right circularly polarized) light excitation, as evident from the near-field distributions. Furthermore, the proposed structure offers multifunctional properties, such as, linear dichroism (LD) of ~ 0.72 at 852 nm and polarization rotation (θ_rot) of ~ 70° at non-resonant wavelength of 1250 nm. Good structural (period variation from 750 to 850 nm) and angular (angle of incidence within ± 10°) tolerance, and multifunctionalities make the proposed Ψ-like metasurface attractive for chiroptical sensing.