Onsager relations and time-reversal symmetry in nonlinear optics

Abstract

Results following from time-reversal symmetry are developed for those nonlinear optical processes where a statistical average is required. These generalize previous analyses by removing the electric dipole approximation and allowing for intermediate resonances. For example, Onsager relations for self-conjugate nonlinear optical processes (when input and output photons form degenerate pairs) are derived and associated reversality relations generalized. In the nonresonant limit magnetic-dipole but not electric-quadrupole terms in coherent processes are suppressed. For general processes purely electric dipole contributions to natural optical activity are possible when intermediate resonances are present.