飞秒脉冲激光在V型有机分子介质中的动力学表征

摘要

We simulate the propagation of the femtosecond laser pulses through the V-type three-level organic molecular medium by numerically resolving Maxwell-Bloch equations using finite-difference time-domain and iterative predictor-corrector technique beyond rotating -wave approximation and slowly varying envelope ap-proximation. The effect of the molecular density on the pulse resonant propagation and the dynamics of two-col-or femtosecond pulses are studied. The electronic structure and dipole moments of the organic molecule are com-puted using the ab initio method at the level of density functional theory. The results show that the concentration of the sample has an obvious effect on the evolution of the pulse. Larger concentration results in stronger nonlin-ear effect, and area theorem becomes invalid as the value of molecular density increases; The relative intensity and the initial phase of two-color pulses have great impact on the population of the levels.%在不采用旋波近似和慢变幅近似的条件下，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，模拟了飞秒激光脉冲在V型三能级有机分子介质中的传播过程，研究了介质密度对单色脉冲共振传播的影响以及两色飞秒脉冲在该分子体系中的传播情况。有机分子的电子结构和电偶极矩是在密度泛函理论水平上利用从头计算方法得到的。研究结果表明，介质密度对脉冲演化产生较大的影响，随介质密度的增大，非线性效应增强，面积定理逐渐失效；两色脉冲的相对强度及初始相位对各能级的粒子数分布有很大的影响。