NONLINEAR PHASE-SHIFT AS A RESULT OF CASCADED 3RD-ORDER PROCESSES

In centrosymmetric media, in addition to the third-and fifth-order non linearity, a cascaded chi((3)):chi((3)) nonlinearity contributes to th e nonlinear refraction. The described effect takes place when the inpu t beam is involved in nearly phase-matched third-harmonic generation. The nonlinear phase shift produced by this new cascaded nonlinearity i s comparable to the nonlinear phase shift caused by the direct third-o rder nonlinearity chi((3)). A new analytical approach, low depletion a pproximation, was developed and used to study the cascaded third-order processes in the conditions of not very high third-harmonic conversio n coefficients. At higher conversion coefficients the effect was studi ed by numerical simulations. The presence of a seeded third-harmonic w ave gives another possibility of controlling the additional phase shif t of the fundamental wave. The conditions for stationary copropagation of the fundamental and the generated wave an presented.