Chiral materials in second-order nonlinear optics

We review how chirality can lead to new types of second-order nonlinear opt ical materials. Chiral molecules are noncentrosymmetric with a nonvanishing electric-dipole-allowed second-order response, which persists in macroscop ic samples with high rotational symmetry such as isotropic solutions. On th e other hand, contributions of magnetic-dipole interactions, which can be s trong in chiral materials, allow second-order processes in centrosymmetric materials. The magnetic contributions of thin films of chiral polyisocyanid es and polythiophenes are comparable to electric contributions. Components of the electric-dipole susceptibility tensor associated with chirality domi nate the response of thin films of a chiral helicenebisquinone.