Optical Stark effect and Kerr nonlinearities of atomic media in nonlinear optical processes

It is shown that the resonant enhancements of the optical Kerr effect and the optical Stark effect of the same order are caused by the same change in the state of an atomic system. The analysis of the known experimental data demonstrates the identity of their influence on nonlinear optical processes. It is shown that a separate analysis of the influence of Stark shift and resonantly enhanced Kerr nonlinearities leads to incorrect results.