Nonlinear chiral imaging of twisted-cross gold nano-objects

Abstract

Chirality, i.e., lack of reflection symmetry, is a property of materials which leads to optical activity (OA) effects [1]. Chiral materials occur in two enantiomers, which are mirror images of each other. In recent years, chiral metamaterials based on metal nanostructures have been shown to lead to greatly enhanced OA effects in the linear optical response [2,3]. On the other hand, second-harmonic generation (SHG) from ideally achiral metal nanostructures is extremely sensitive to chiral symmetry breaking due to surface defects [4]. It is therefore important to study whether nonlinear techniques can be used as a probe of the handedness of chiral metamaterials fabricated using state-of-the art techniques. Here we demonstrate that SHG microscopy with circularly-polarized light possesses an unambiguous sensitivity to the handedness of twisted-cross metamaterials to the level of individual subwavelength-sized nano-objects.