较高阶非线性抽运-探测过程中的空间效应

在飞秒抽运一探测光谱技术中，空间分辨的探测光信号反映了在不同空间位置的材料的非线性效应。当抽运光强度增大时，探测光信号中会出现明显的高阶特别是五阶非线性效应。利用劈裂算子方法直接解决了一维非线性传播方程的问题。在数值模拟中，研究了在不同抽运强度和位置下的抽运一探测过程中的五阶非线性效应。在足够高的抽运场下，探测信号出现清晰的振荡，显示了三阶和五阶非线性效应之间的干涉。当空间位置离抽运场中心足够远时，五阶比三阶非线性效应的衰减快得多，对其物理机制和趋势进行了定性的讨论。

In femtosecond pump-probe spectroscopy, spatial resolved probe signal reflects the nonlinear effects of the sample in different spatial positions. However, as the pump intensity increases, high order, especially fifth-order nonlinear effects will appear in the probe signal. The split-step method is used to directly solve the nonlinear propagation equation with one transverse dimension. In the numerical simulation, the effects of fifth-order nonlinearity in pump probe process are studied for different pump intensities and spatial positions. For sufficient intense pump field, the probe signal show distinct interference between the third- and fifth-order nonlinear polarization. Clearly oscillation has been observed in the signal. At the spatial position far away from the center of the pump field, the fifth-order contribution of the probe decays much faster than the third-order contribution. The physical mechanism and intention are discussed qualitatively.