Second-harmonic generation in centrosymmetric crystals of chiral molecules

We demonstrate that for centrosymmetric structures of chiral molecules the interaction with circularly polarized light gives rise to nonzero second-order susceptibilities. It is ascribed to transitions that are both magnetic and electric dipole allowed. Experimental demonstration is given of second-harmonic generation from centrosymmetric crystals of R,S-N-acetyl valine (P$2_1$/c) using a fundamental wave having elliptic polarization in most parts of the trajectory through the crystal. These results demonstrate the existence of optical activity in the hyperpolarizability term β, similarly to the well-known optical-rotation phenomena in the linear polarizability.