超短脉冲激光在DBASVP分子中传播时的双光子面积演化和光限幅效应

Two-photon area evolution and optical limiting of ultrashort laser pulses in DBASVP molecule media

以一维不对称π共轭分子体系(DBASVP分子)为介质,在双光子共振条件下,从双光子面积定理和严格数值求解Maxwell-Bloch方程两方面出发,分别研究超短脉冲激光在该有机分子介质中的传播过程,从而探讨双光子面积的演化规律,并分析双光子面积定理的适用性.提出了一种数值模拟分子介质光限幅特性的理论方法.分子的电子结构和电偶极矩是基于密度泛函理论利用从头计算方法得到的.研究结果表明,基于慢变幅和慢变相近似以及单模场条件下的双光子面积定理不能很好地描述超短脉冲的双光子面积在该分子介质中的演化规律.基于双光子吸收的分子光限幅特性与分子介质的厚度有关.

Taking the one-dimensional asymmetrical π conjugation molecule material （DBASVP molecules） as medium, with the two- photon resonance, we studied the propagation of ultrashort laser pulses in the medium based on the two-photon area theorem and the numerical solutions of the coupled Bloch and Maxwell＇ s equations. The evolution of two-photon area is thus investigated and the applicability of the two-photon area is then discussed. A theoretical method for simulating the optical limiting properties of molecular medium is pointed out. The molecular electronic structures and dipole moments are calculated by use of density functional theory at ab initio level. The numerical results show that the two-photon area theorem based on the slowly varying envelope and phase approximations cannot accurately describe the evolvution of the two-photon area in the molecular medium. The optical limiting behavior based on the two-photon absorption is related to the width of the molecular medium.