超短激光双脉冲在硝基苯胺分子介质中传播的动力学过程

Propagation dynamics of double ultrashort laser pulses in a para-nitroaniline molecule medium

通过数值求解麦克斯韦-布洛赫方程,研究了2个相干超短激光脉冲在硝基苯胺分子(pNA分子)介质中的非线性传播过程.量化计算表明该分子在低能级区域内只有1个电荷转移态,因此可把该分子看作二能级体系.当3π共振脉冲与4π非共振脉冲先后入射到硝基苯胺分子介质中进行传播时,3π脉冲的能量将转移给后面的4π脉冲,前者面积逐渐变为2π,激发分子能级占有率发生一次完整的拉比振荡;后者在介质中仍保持非共振传播,只能激发分子能级占有率发生不完整的拉比振荡.脉冲的频谱发生展宽,并在共振频率附近振荡剧烈.通过引入固有偶极矩为零的赝分子作为比较对象,发现硝基苯胺分子的固有偶极矩导致非线性传播过程更为复杂.

By numerically solving the Maxwell-Bloch equations, the nonlinear propagation of two coherent ultrashort laser pulses in a para-nitroaniline molecule medium is investigated. The theoretical computations indicate that the molecule has only one charge-transfer state in lower energy region, and consequently the molecule can be regarded as a two-level system when studying the interaction of the molecule medium with laser pulses. When a 3π resonant pulse followed by a 4π nonresonant pulse enters into the molecule medium, the 3π pulse transfers its energy to the latter 4π pulse, and then the area of former pulse approaches 2π, only driving one complete Rabi flopping of population. The 4π pulse keeps a nonresonant propagation in the medium and only excites some incomplete Rabi floppings. The corresponding spectrum range broadens, and spectral components around the resonant frequency oscillate sharply. By introducing a pseudo-molecule without per-manent dipole moments as a comparison object, it is found that the propagation dynamics becomes more complex due to the permanent dipole moments of para-nitroaniline molecule.