PHENOMENOLOGICAL DAMPING OF NONLINEAR-OPTICAL RESPONSE TENSORS

The damping factors that occur in nonlinear-optical response tensors a re commonly assigned signs that depend upon the temporal ordering of t he associated photon interactions. However, time-reversal symmetry is satisfied only if all these signs are identical. For example, only the n is there a formal equivalence between the amplitudes for second-harm onic generation and parametric down-conversion and only then is electr o-optic rotation forbidden in fluids. This correction reflects deficie ncies in certain commonly employed semiclassical approaches to nonline ar optics.