Journal of Chemical Physics, Vol.100, No.9, 6535-6542, 1994
Explicit Nondivergent Formulas for Atomic and Molecular Dynamic Hyperpolarizabilities
Two methods are used to develop nondivergent, compact, sum-over-states formulas for dynamic hyperpolarizabilities up to fifth order. Expressions for both atoms and molecules are given; those at fourth and fifth order for the first time. The fifth-order formula is related to such nonlinear optical phenomena as stimulated hyper-Raman scattering and the self-induced intensity-dependent refractive index. Questions of time-reversal invariance are also discussed. Importantly, the derivations explicitly take into account secular divergences in a simple and clear way.