Nonlinear phase shift via multistep χ(2) cascading

We present the first (according to our knowledge) consideration of the influence of the three- and four-step second-order nonlinearity cascading in the process of the nonlinear phase shift of the fundamental wave involved simultaneously on two nonlinear optical processes: second harmonic generation and sum frequency mixing. Under the condition that the two processes are nearly phase matched, the presence of multistep cascading leads to four times reduction of the input intensity necessary for obtaining a value of pi for the nonlinear phase shift. (C) 1998 Elsevier Science B.V. All rights reserved.