飞秒激光场中原子所受光学偶极力研究

通过求解全波矢布洛赫方程研究了两能级原子与飞秒超快激光脉冲的相互作用过程,计算了不同拉比频率取值下原子所受光学偶极力和粒子数布居随时间的演化情况,分析了光场失谐量对光学势分布情况的影响.研究发现:由飞秒激光场产生的横向光力的时间平均值并不等于零,而是随着拉比频率的增加呈现振荡的增大趋势;纵向光力的时间平均作用也并非是拉比频率的单调函数,而是随着拉比频率的增加呈现周期性的振荡分布特性;光学势的分布对光场的失谐量具有明显的依赖性,随着失谐量的变化,光学势的性质也随之发生了改变.     

Carrier--envelope phase effects for a dipolar molecule interacting with ultrashort laser pulse

In this paper the phase-dependent features of ultrashort laser pulse resonant propagation in a two-level dipolar molecule are demonstrated by solving full Maxwell--Bloch equations. The electronic properties of dipolar molecule 4-trans-[p-(N, N-Di-n-butylamino)-p -stilbenylvinyl] pyridine (DBASVP) molecule, one-dimensional asymmetric organic molecule, is calculated by density functional theory at \textit{ab initio} level. The numerical results show that the carrier propagation and the spectrum evolution of the pulse are sensitive to its initial phase and the phase sensitivity is more obvious for larger area pulse. The phase-dependent feature is more evident in dipolar molecule because the permanent dipole moment makes the nonlinear effects stronger.     

飞秒激光脉冲在三能级有机分子介质中传播时的频谱分析

通过采用预估校正的时域有限差分法求解麦克斯韦-布洛赫方程,我们研究了飞秒激光脉冲在三能级有机分子(4,4-二甲氨基二苯乙烯分子)介质中传播时脉冲的频谱演化情况.在单光子共振情况下,即入射脉冲频率等于1、2能级之间的共振频率,对大面积入射脉冲,由于强的二次激发的作用,电场频谱中出现了在ω32附近振荡的频率成分,ω32是2、3能级之间的共振频率,说明对大面积入射脉冲二能级模型已经失效,需要采用多能级模型来描述分子介质.在双光子共振情况下,即入射脉冲频率等于1、3能级之间的共振频率的一半,由于介质中放大的自发辐射和四波混频的作用,部分入射脉冲能量转化为高频和低频电场成分的能量,分子介质表现出了很强的光功率限幅特性.     

Dynamics of cooperative emissions in a cascade three-level molecular system driven by an ultrashort laser pulse

This paper investigates the dynamics of cooperative emissions in a cascade three-level system driven by an ultra, short laser pulse by solving numerically the full-wave Maxwell-Bloch equations. The 4, 4＇-bis（dimethylamino） stilbene molecule is used as the model molecule because of its strong two-photon absorption property. The two-colour cooperative emissions are studied as functions of molecular number density and dephasing rate of the dipole coherence. The propagation effects on the evolution of the cooperative radiations are also taken into account. The cooperative radiations are enhanced for large number density of the molecule, while the fast dephasing of the dipole coherence reduces the intensity of the cooperative radiations and delays the emission times or even inhibits the formation of the emissions. The delay time of the radiation decreases with the increase of the molecular number density and the propagation distance.     

Quantum Dissonance as an Indicator of Quantum Phase Transition in the XXZ Chain

We investigate the behavior of quantum dissonance in the anti-ferromagnetic XXZ spin S = 1/2 chain, which exhibits a quantum phase transition. Based on a unified view of quantum and classical correlations, quantum dissonance is analytically calculated and is compared with entanglement, discord, and classical correlations for the ground state of the system. It is found that the nearest-neighbor quantum dissonance achieves an extremum and exhibits the sharpest change at the critical point. Therefore, quantum dissonance may serve as a more efficient indicator of quantum phase transitions in the XXZ spin chain.     

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     

含时电离对分子动态双光子吸收截面的影响

通过采用时域有限差分法和预估矫正法数值求解麦克斯韦-布洛赫方程,研究了含时电离对分子材料4,4'-二甲氨基二苯乙烯的动态双光子吸收截面的影响.研究结果表明,对周期量级的飞秒脉冲,介质发生的主要是一步共振双光子吸收,入射光强较高时出现双光子吸收饱和现象,入射光强小于双光子吸收饱和光强时介质的双光子吸收截面随入射光强的增大线性减小.在不同的传播距离处,分子的双光子吸收截面有较大的差别,因此,在对不f川的实验条件下测得的双光子吸收截而数值进行比较时,需要考虑样晶厚度对实验结果的影响.在同一传播距离处,随光电离截面取值的增人介质的双光子吸收截面减小.利用匕秒脉冲测量分子的双光子吸收截面时,通过数值模拟,讨论了已有解析结果的适用条件.     

Numerical analyses on optical limiting performances of chloroindium phthalocyanines with different substituent positions

Optical limiting properties of two soluble chloroindium phthalocyanines with α- and β-alkoxyl substituents in nanosecond laser field have been studied by solving numerically the coupled singlet–triplet rate equation together with the paraxial wave field equation under the Crank–Nicholson scheme. Both transverse and longitudinal effects of the laser field on photophysical properties of the compounds are considered. Effective transfer time between the ground state and the lowest triplet state is defined in reformulated rate equations to characterize dynamics of singlet–triplet state population transfer. It is found that both phthalocyanines exhibit good nonlinear optical absorption abilities, while the compound withα-substituent shows enhanced optical limiting performance. Our ab-initio calculations reveal that the phthalocyanine withα-substituent has more obvious electron delocalization and lower frontier orbital transfer energies, which are responsible for its preferable photophysical properties.     

Optical power limiting of ultrashort hyper-Gaussian pulses in cascade three-level system

Propagation of strong femtosecond hyper-Gaussian pulses in a cascade three-level molecular system is studied by solving numerically the Maxwell–Bloch equations by the iterative predictor-corrector finite-difference time-domain method.Optical power limiting behavior induced by strong nonlinear two-photon absorption is observed for different orders of the femtosecond hyper-Gaussian pulses. Pulses of a higher order temporal profile are found to have a wider power range of optical limiting but a larger output saturation intensity. Both the output saturation value and the damage threshold of optical power limiting decrease with pulse duration increasing. The decrease of the pulse area along the pulse propagation is much slower than that obtained from the two-photon area theorem due to invalidity of the slowly varying amplitude approximation and the monochromatic field hypothesis.