Chiral materials in second-order nonlinear optics

Abstract

We review second-order nonlinear optical properties of chiral materials from the viewpoint of new second-order materials. Chiral molecules are noncentrosymmetric and therefore have a nonvanishing electric-dipole-allowed second-order response. The response is nonvanishing even in macroscopic samples with no polar order including isotropic solutions. Magnetic-dipole interactions of chiral materials can be strong. Their contributions to the nonlinear response allow second-order processes even in centrosymmetric materials. The magnetic contributions to the second-order response of thin films of chiral polyisocyanides and polythiophenes are comparable to the electric contributions. The chiral part of the electric-dipole-allowed nonlinearity dominates the second-order response of thin films of a chiral helicenebisquinone. Quasi-phase-matched second-harmonic generation was demonstrated in alternating stacks of the two enantiomers of the helicenebisquinone.