含时电离对飞秒脉冲激光在强双光子吸收介质中传播特性和光限幅行为的影响

以具有强双光子吸收特性的4,4′-二甲氨基二苯乙烯分子体系为研究对象，通过采用时域有限差分法和预估矫正法数值求解Maxwell-Bloch方程，模拟了飞秒脉冲在该分子介质中的传播过程，研究了含时电离对双光子吸收过程和光限幅行为的影响.研究结果表明，光电离使介质与光场的非线性相互作用减弱，同时自发辐射降低， 随着入射电场的增强，光电离对主脉冲演化有明显的影响.光电离使介质的光限幅失效行为减弱.随着光电离截面增加，光限幅的动力学窗口变宽，表明了光电离有利于增强介质的光限幅效应.在不同的传播距离处，脉冲传播呈现 关键词： 含时电离 双光子吸收 光限幅效应 超短脉冲激光

Effect of time-dependent ionization on properties of the ultrashort pulse propagation and optical power limiting in a two-photon absorption molecular medium

By taking the strong two-photon absorption 4,4′-bis （dimethylamino） stilbene molecules as medium, the propagation of femosecond laser pulses in this medium is simulated by numerically solving the Maxwell-Bloch equations using an iterative predictor-corrector and finite-difference time-domain method. The influences of time-dependent ionization on two-photon absorption and optical power limiting behavior are emphatically investigated. The numerical results show that the nonlinear interactions between the pulses and the medium and the corresponding spontaneous emission become weaker when the time-dependent photoionization is considered. The effects of photonionization on the main pulse become more evident as the amplitude of input electric field is increased. When the photonionization cross section is larger, the dynamic optical limiting range becomes broader, which demonstrates that the limited photonionization ability is favorable for the optical power limiting. Furthermore, the propagating-distance dependence of the dynamical behavior of the ultrashort laser pulse in the medium is observed.