Mid-infrared gyrotropy in split-ring resonators measured by Mueller matrix ellipsometry

Abstract

Understanding gyrotropic effects in the mid-infrared (MIR) spectral range is of high technological interest because it is the fingerprint region of many metamaterials and organic compounds. We present experimental and simulated ellipsometric measurements of gyrotropy in the MIR region upon reflection from an ordered array of split-ring resonators, which are inherently non-chiral. We use the symmetry properties of the Mueller matrix for interpretation of the ellipsometric measurements and to identify gyrotropy. When the plane of incidence coincides with the low-symmetry optical axis, we observe gyrotropy at oblique incidence. The origin of the gyrotropy is explained by considering not only the electric dipole–magnetic dipole interaction, as in natural optical activity, but by retaining the electric dipole–electric quadrupole contributions. In isotropic systems these average to zero, however they are significant in ordered systems such as crystals and metamaterials.