“Extrinsic optical chirality” and resonant absorption in GaAs-based nanowires investigated by photo-acoustic spectroscopy

In this work we report on the resonant absorption properties of GaAs-based nanowires, and on the chiral response when such nanowires are asymmetrically covered by gold. We use photo-acoustic spectroscopy which is a scattering-free, stable and highly sensitive technique that directly measures the absorption of the nanowire ensembles. Highly uniform samples were fabricated by lithography-free process of selfcatalyzed growth on Si substrates. We report on the experimental resonant absorption in the range (300÷1100) nm, which is in great agreement with simulations. We then measure the circular dichroism at 532nm, and discuss on the formation of near chiral fields for enhanced enantioselectivity applications.