周期量级超短脉冲激光在有机分子材料中的传播

利用从头计算方法,在密度泛函理论上,计算了硝基苯胺(para-Nitroaniline,pNA)分子的电偶极距.通过严格求解麦克斯韦-布洛赫方程,研究了周期量级超短脉冲激光与硝基苯胺分子材料的相互作用,研究显示当超短脉冲在分子中共振传播时,会出现高频与低频成分,随传播距离的增加.频谱的展宽越来越明显,而分子能级占有率之差在电场为零时,表现出一种台阶的特征;当超短脉冲激光在该分子介质中非共振传播时,脉冲激光频谱中明显地出现了二次谐波成分.     

超短脉冲激光在硝基苯胺分子材料中的非共振传播

通过严格求解麦克斯韦-布洛赫方程,研究了超短脉冲激光与硝基苯胺分子材料的非共振相互作用.研究结果表明,当脉冲激光在该分子介质中以电荷转移态的激发能的二分之一非共振传播时,脉冲激光频谱中明显地出现了二次谐波成分,显示了该分子具有较强的双光子吸收性质.     

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     

脉冲激光在有机分子材料中的共振传播

利用麦克斯韦-布洛赫耦合方程,研究了激光脉冲在4,4′-二甲氨基二苯乙烯分子材料中的共振传播,探讨了激光脉冲在传播中的时空演化情况.在数值计算中考虑了各种阻尼效应.     

静电场诱导的分子双光子吸收截面和光限幅性能的变化

采用时域有限差分法数值求解麦克斯韦-布洛赫方程,研究了当存在静电场时少周期脉冲激光在4,4'-二(二正丁胺基)二苯乙烯(BDBAS)分子介质中的传播过程,得到了分子的动态双光子吸收(TPA)截面并且展示了其光限幅行为. 由于静电场的存在打破了BDBAS分子的对称性,因此激光在传播过程中,其频谱同时出现了偶次谐波和奇次谐波. 随着静电场强度的增加,分子的动态TPA截面增大,同时光限幅效应更为明显.     

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.     

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

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. 关键词： 双光子吸收 光限幅效应 双光子面积定理 超短脉冲激光     

共振原子蒸气中激光脉冲的时空特性

在柱对称条件下，利用耦合的布洛赫－麦克斯韦方程，研究了激光脉冲在原子蒸气介质中的共振传播。考察了脉中在时空中的演化。数值计算结果表明激光脉冲在传播中，由于自感应透明与光波的衍射效应，表现出复杂的相干现象。     

飞秒脉冲激光在V型有机分子介质中的动力学表征

在不采用旋波近似和慢变幅近似的条件下,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,模拟了飞秒激光脉冲在V型三能级有机分子介质中的传播过程,研究了介质密度对单色脉冲共振传播的影响以及两色飞秒脉冲在该分子体系中的传播情况.有机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,介质密度对脉冲演化产生较大的影响,随介质密度的增大,非线性效应增强,面积定理逐渐失效;两色脉冲的相对强度及初始相位对各能级的粒子数分布有很大的影响.     

飞秒脉冲激光在V型有机分子介质中的动力学表征

在不采用旋波近似和慢变幅近似的条件下,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,模拟了飞秒激光脉冲在V型三能级有机分子介质中的传播过程,研究了介质密度对单色脉冲共振传播的影响以及两色飞秒脉冲在该分子体系中的传播情况。有机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,介质密度对脉冲演化产生较大的影响,随介质密度的增大,非线性效应增强,面积定理逐渐失效;两色脉冲的相对强度及初始相位对各能级的粒子数分布有很大的影响。     

Resonant propagation of femtosecond laser pulse in DBASVP molecule：one-dimensional asymmetric organic molecule

We have investigated the resonant propagation of femtosecond laser pulse in 4-trans-[p-（N, N-Di-n-butylamino）- p-stilbenyl vinyl] pyridine medium with permanent dipole moments. The electronic structures and parameters for the compound have been calculated by using density functional theory. In the optical regime, there is one charge-transfer state, and the molecule can thus be simplified as a two-level system. Both the one- and two-photon transitions occur between the ground and charge-transfer states. The numerical results show that the permanent dipole moments have an obvious effect on the propagation of the ultrashort pulse laser. The ideal self-induced transparency disappears for 2π pulse, and second harmonic spectral components occur significantly due to the two-photon absorption process. For the 6π pulse, continuum frequency generation is produced and a shorter duration pulse in time domain with 465 as is obtained.     

New class of extremely short electromagnetic solitons

A physical realization is presented for the integrable modified sine-Gordon equation. In this case, this equation describes the propagation of an extremely short vector electromagnetic pulse in the system of asymmetric quantum objects that have permanent dipole moments in the self-energy states. Using soliton solutions for ordinary and extraordinary components, new regimes of the dynamics of the pulse and medium that are specific only to asymmetric media have been found.     

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.     

Effect of the ratio of transition dipole moments on few-cycle pulse propagation

Propagation of a few-cycle laser pulses in a dense V-type three-level atomic medium is investigated based on full-wave Maxwell-Bloch equations by taking the near dipole-dipole (NDD) interaction into account. We find that the ratio, γ, of the transition dipole moments has strong influence on the time evolution and split of the pulse: when γ≤ 1, the NDD interaction delays propagation and split of the pulse, and this phenomenon is more obvious when the value of γ is smaller; when γ = 2, the NDD interaction accelerates propagation and split of the pulse.     

Extremely short and quasi-monochromatic electromagnetic solitons in a two-component medium

The propagation of extremely short (without high-frequency filling) pulses and nonresonant envelope solitons in a two-component medium comprising two-level atoms with substantially different quantum transition frequencies was studied. The dynamics of a pulse whose reciprocal time scale lay between these frequencies was shown to be described by the Kosevich-Kovalev equation, the one-way variant of which was the Konno-Kameyama-Sanuki equation. If the transition dipole moments of medium components were equal, the one-way equation became integrable. Soliton and soliton-like solutions to these equations were used to analyze pulse propagation regimes at various two-component medium initial states. The stability of these localized wave formations was analyzed. The possible existence of stable soliton-like pulses propagating in a nonequilibrium medium at group velocities exceeding the velocity of light in vacuum was discussed.     

Optical Rectification and Generation of Harmonics Under Condition of Propagation of Few-Cycle Pulses in the Birefringent Medium with Asymmetric Molecules

Without using the approximation of slowly varying envelopes, we investigate spectral transformations of vector few-cycle and quasi-monochromatic solitons under propagation in the birefringent medium of asymmetric molecules possessing permanent dipole moments. We show that when an ordinary pulse enters the medium, the self-modulation effect arises. As a result, the spectrum of the ordinary component undergoes significant changes from the violet shift and the generation of odd harmonics with close frequency satellites to the supercontinuum including zero frequency. The spectrum of the extra-ordinary few-cycle pulse also has the properties of a supercontinuum. When a quasi-monochromatic ordinary pulse enters the medium in the spectrum of an extra-ordinary component, the effect of optical rectification with simultaneous generation of the second harmonics is clearly manifested.     

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.     

Solvent Dependence on Structure and Electronic Properties of 7-(Diethylamino) - 2H -1- Benzopyran-2- one (C-466) Laser Dye

In this work, we studied influences on the absorption and fluorescence emission spectra of coumarin-4066 (C-466) with different solvent polarity scale. The spectral shifts reflect the effect of the equilibrium solvents association across the energized solute particle, which adjusts inertially as a result of quick charge realignment upon radiative deactivation to the lowest electronic state. The dipole moments of C-466 are determined by employing the Bakhshiev, Kawski-Chamma-Viallet, Lippert-Mataga and McRae relations. The results from all these methods are, excited state dipole moment of C-466 is higher than the ground state dipole moments and which indicates molecule is less polar in the ground state. Theoretical analysis was also carried out by Density Functional theory (DFT and TD –DFT) employing the BECKE-1998 (exchange)/STO-6G basic set in ethanol solvent and in vacuum medium. The HOMO-LUMO, Solvent Accessible Surfaces (SAS) and Molecular Electrostatic Potential (MEP) were analysed to acquire additional knowledge of the molecular arrangement and electronic properties of C-466. These photophysical properties suggest delineation can be mauled for laying out new luminescent tests for various solvents microenvironment.