Two‐photon circular dichroism

Equations for two−photon circular dichroism are presented. Two−photon circular dichroism is the difference in absorption coefficient for two left circularly polarized photons and for two right circularly polarized photons. In an unoriented solution only chiral (optically active) molecules can exhibit circular dichroism. The circular dichroism depends on the directions of propagation of the two photons. Parallel propagation, antiparallel propagation, and perpendicular propagation provide independent measurements of the contributions to the circular dichroism. These contributions can similarly be obtained with one circularly polarized photon plus one linearly polarized photon. The two−photon circular dichroism depends on transition electric dipole moments, transition magnetic dipole moments, and transition electric quadrupole moments; it should help in the study of chiral molecules.