Cross-phase-modulation-induced nonlinear diffraction wave

We present and discuss a type of nonlinear diffraction wave (NLDW) induced by the strong cross-phase-modulation (XPM) effect between the femtosecond pump wave (FW) and its second-harmonic wave (SHW), observed experimentally in periodically poled lithium niobate (PPLN) nonlinear gratings. We develop a modified femtosecond pulse propagation model that describes the evolution of FW and SHW under the participation of the XPM effect. This model is numerically solved using the split-step Fourier transformation method, and the results successfully explain the experimentally observed XPM-NLDW phenomenon. The discovery and analysis of XPM-NLDW will provide a deeper insight into the synergic nonlinear effects arising from the interaction of a femtosecond laser pulse with the PPLN crystal and stimulate the exploration of many other unknown phenomena existing in this regime of nonlinear optics.