级联三能级模型下超短脉冲激光与分子相互作用的动力学研究

通过求解麦克斯韦-布洛赫方程，研究了超短脉冲激光和一维对称π共轭分子材料(4,4′-二甲氨基二苯乙烯分子)的相互作用.该分子材料具有较强的非线性光学性质，其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，慢变幅近似和旋波近似不能很好地描述超短脉冲在该分子介质中的传播.在单光子共振情况下，保持入射脉冲的脉冲宽度不变，当小面积脉冲在该分子介质中传播时，二能级模型可以较好地描述脉冲激光与该分子体系的相互作用过程.但对于大面积脉冲激光，由于较明显地产生了分子的二次激发，此时分子 关键词： 超短脉冲激光 4′-二甲氨基二苯乙烯分子 三能级模型 麦克斯韦-布洛赫方程

Dynamical behavior of ultra-short laser pulse in a cascade three-level molecular system

We study the interaction between the ultra-short laser pulses and the one-dimensional symmetrical π conjugated molecular material (4,4′-bis (dimethylamino) stilbene) by solving Maxwell-Bloch equations. This kind of molecular material has strong nonlinear optical properties, and its electronic structures and dipole moments are calculated by use of density functional theory on ab initio level. The numerical results show that the slowly varying envelope approximation and the rotating wave approximation cannot accurately describe the propagation properties of the ultra-short pulse in the molecular medium. In the case of single photon resonance, the two-level model can well describe the interaction between the small area pulse and the molecular system. For large area pulse, due to the existence of strongly secondary excitation to the higher-lying levels, the three-level model should be used. When the amplitude of the incident electric field is kept constant, the third level's population increases with the increase of the pulse area.