Optical activity in chiral gold nanogratings

Nanogratings consisting of chiral gold particles were fabricated employing electron beam lithography, lift-off and argon sputter etching. Spectra of the transmittance and chirality induced polarization azimuth rotation of nanogratings were measured. A giant specific polarization azimuth rotation (∼104 deg/mm) was observed near surface plasmon resonance. We found that the rotation direction changes its sign with a handedness of chiral particles. However, it remains the same for the light incident to the front and back sides of the specific grating, i.e., the effect is reciprocal and manifests conventional optical activity.