An overview of optical extrinsic chirality of metasurfaces is presented. Even non-chiral objects can exhibit effective optical chiral response due to particular symmetry breaking of the investigating light and the sample morphology. Here we show linear and nonlinear optical measurements performed on a metasurface composed by different kind of self-assembled nanowires on a substrate, such as metal nanowires and semiconductor nanowires. The measurements are performed in three different schemes: optical reflectance, photoacustic absorbance and second harmonic generation. In all these schemes circular polarized light was used in order to evidence the optical chiral behavior in different reciprocal disposition of the metasurfaces and light direction. The circular dichroism results to be present in all schemes when the three directions formed by ⅰ) the sample orientation, ⅱ) the impinging light wave vector and ⅲ) the normal to the metasurface form a non-planar triad. Indeed non-planar triad of vectors represents a system that cannot be superposed to its mirror image, thus it is chiral system.
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