Broadband Depolarization via Plasmonic Metasurfaces: Conversion from Purely Polarized to Absolute Unpolarized States

We investigate the ability of a plasmonic metasurface to transform the state of polarization of incident light from purely linear to an absolute unpolarized state or zero degrees of polarization. This transformation occurs when the light interacts with an array of gold split-ring nanoresonators at normal angles with its scattering detected along the plane of the array (in-plane scattering). Our findings reveal that within certain wavelength ranges, the state of polarization of the in-plane scattering transitions into a complete pseudorandom state. This underscores the influence of interference effects associated with multipolar plasmon resonances, the impact of lattice modes, and the metasurface's capability to selectively filter specific polarization states from its scattering when detected along the plane of the array. The absolute pseudounpolarized state manifests differently at various wavelengths depending on the directions of the incident light's polarization axis and the sides of the arrays. We demonstrate that the wavelengths at which this phenomenon occurs vary with the angle of the incident light's polarization axis.