One- and two-photon absorption properties of two metalloporphyrin complexes

The linear and nonlinear optical properties of two metalloporphyrin complexes formed by the complementary coordination of central zinc or magnesium ions to the ligand 5, 10, 15-tri-(p-tolyl)-20-phenylethynylporphyrin are theoretically investigated by using the analytic response theory at the density functional theory level. The results indicate that the studied complexes present more symmetric geometry structures than the ligand. The charge-transfer states of the two complexes in the lower energy region are all almost degenerate but those of the ligand are well separated. The ratio of the two-photon absorption cross sections of the ligand, zinc-porphyrin and magnesium-porphyrin complexes is 1.0:1.5:1.8, demonstrating that the two-photon absorption capability can be greatly increased when the ligand is coordinated with a metal ion. Moreover, several physical micro-mechanisms including electron transitions and intramolecular charge-transfer processes are discussed to explore the differences in optical property between the ligand and two complexes.     

Effect of Lorentz local field correction on propagation of ultrashort laser pulse in one-dimensional para-nitroaniline (PNA) molecules

This paper investigates the effect of Lorentz local field correction (LFC) on the propagation of ultrashort laser pulses in a para-nitroaniline molecular medium under resonant and nonresonant conditions by solving numerically the full-wave Maxwell-Bloch equations beyond slowly-varying envelope approximation and rotating-wave approximation. The effect of the LFC is considerably obvious when pulses with large areas propagate in the dense molecular medium. In the case of resonance,the group velocity of the sub-pulses split from the incident pulse along propagation is severely decreased by the LFC,especially for the latest sub-pulse. However,in the case of nonresonance,the influence of the LFC on the temporal evolution of the pulse is less obvious and lacks homogeneity with an increase in incident pulse area,propagation distance and molecular density.     

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.     

吡嗪分子在硅(100)面吸附构型的XPS和NEXAFS谱理论研究

本文利用X射线谱研究了吡嗪(C₄H₄N₂)分子共价吸附于硅(100)面的几种吸附构型的几何结构和电子结构. 利用密度泛函理论结合团簇模型，对预测的吸附结构的碳K壳层(1s)X射线光电子能谱(XPS)和近边X射线吸收精细结构(NEXAFS)谱进行了模拟. 计算结果阐明了XPS和NEXAFS谱与不同吸附构型的对应关系. 与XPS谱相比，NEXAFS谱对所研究的吡嗪/硅(100)体系的结构有明显的依赖性，可以很好地用于结构鉴定. 根据碳原子的分类，研究了在NEXAFS光谱中不同化学环境下碳原子的光谱成分.     

氧化石墨烯-卟啉复合材料光限幅性能的理论研究

利用时域有限差分法数值求解速率-场强方程,研究了一系列共价连接的氧化石墨烯-卟啉复合材料在纳秒时域内的光限幅性质和双光子吸收. 计算结果表明,氧化石墨烯-卟啉复合分子与单独的卟啉分子相比展现出增强的光限幅效应,并且有着更大的双光子吸收截面.与之前得到的含重金属的卟啉分子具有更强非线性光学性质的结论不同,不含金属元素的卟啉分子与氧化石墨烯结合后展现出了更强的非线性光学性质. 理论计算的结果与实验测量符合较好. 此外,着重研究了介质的厚度和脉冲宽度对分子双光子吸收截面的影响. 结果表明,随着介质厚度的增加或者脉宽的变宽分子的动态双光子吸收截面增大.     

门电场对有机单分子器件的影响 (cited: 3)

基于第一性原理和弹性散射格林函数方法,从理论上研究了门电场对一系列有机单分子结的电输运性质的影响. 结果显示,含有氧化还原中心并且在门电场方向具有较大电偶极矩的分子结能够对门电场有显著响应. 2,5-二甲基噻吩二硫醇的伏安特性显示了类似N-沟道金属氧化物半导体管性质. 这一独特的伏安特性可以从能级、耦合能以及原子电荷随门电场的演化来理解.     

联苯二胺分子器件电输运特性的取代效应

在第一性原理基础上,理论研究了苯环上含有不同取代物的四个联苯分子的电输运特性。计算结果表明，当苯环上的氢被取代时，联苯分子的两个苯环之间的扭转角增大。分子结的电导随苯环间扭转角的增加而减少,且电导值与扭转角余弦平方成线性关系。在低偏压下，分子结的电输运机制是电子通过 轨道的隧穿过程。计算结果与实验结果符合的较好。     

电极接触构型对辛烷硫醇分子非弹性电子隧穿谱的影响

本文选取辛烷硫醇分子通过终端S原子化学吸附于一端的Au原子团簇,另一端由碳原子物理吸附于Au原子团簇形成分子结,利用从头计算方法和非弹性散射格林函数理论研究了在三种不同电极接触构型下的该分子的非弹性电子隧穿谱的影响.计算结果表明,电极接触构型对分子体系的非弹性电子隧穿谱有着明显的影响.该工作有利于确定实验中分子电子学器件的电极接触构型.     

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.     

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