Optical activity in the hyperpolarizability

It was demonstrated that second harmonic generation (SHG) can be obtained from centrosym. crystals of a racemic mixt. of chiral mols. Circular polarization of the fundamental wave is a prerequisite to obtain selectivity in the interaction of the fundamental wave with one of the enantiomers in the racemic mixt., furnishing a distortion of the centrosymmetry. An explanation is presented to show that this SHG originates from a transition that is both allowed for the elec. dipole and the magnetic dipole, resulting in a correction term in the hyperpolarizability, b. This correction to b is similar to the correction of the polarizability, better known as the optical activity. Therefore, the phenomenon described in this paper is refered to as the optical activity in the hyperpolarizability and can be represented by eehc(2)(-2w;w,w):E(2w).E(w).H(w). Furthermore, theory and preliminary exptl. evidence are presented for the existence of a heec(2)(-2w;w,w):H(2w).E(w).E(w) effect. In this case SHG from centrosym. crystals of a racemic mixt. is the result of a linear polarized incident beam and a nonvanishing radiating magnetic dipole transition. [on SciFinder (R)]