碳分子线C5在激光场中的含时密度泛函理论研究

运用含时密度泛函理论和分子动力学相结合的方法, 研究了C₅分子线在强激光场中的电离激发.研究发现, 当考虑激光强度对C₅分子线激发的影响时, 激光强度越强, 分子吸收的能量越多, 电离也越早, 最终电离的电子也越多, 而且沿激光极化方向的偶极矩的变化及峰值也越大. 关于激光极化方向对C₅分子线激发的影响的研究表明, 当激光极化方向沿着C₅分子线轴向时, 分子的电离大大增强, x方向的激光脉冲仅能激发起x方向的偶极振荡, 而y方向的激光脉冲仅能激发起y方向的偶极振荡, 而且x方向的激光脉冲激发的偶极振荡强. 研究还表明, 当激光极化方向沿着C₅分子线轴向时, 尽管由于电离增强而导致C₅分子线C–C键振动的同步性变差, 但在两种激光极化方向情况下, C₅分子线的振动模式与中性C₅分子线的振动模式相同. 关键词： 含时密度泛函理论 分子动力学 分子电离 碳分子线     

CO分子在线性极化飞秒激光场中的TDDFT研究

本文运用将含时密度泛函理论和分子动力学非绝热耦合的方法,研究了CO分子在不同强度、不同极化方向的激光场中的电离和动力学行为. 研究发现,激光强度越强,CO分子吸收的能量越多,电离越早且电离越强,CO分子键长变长且伸缩振动越剧烈. 此外,CO分子偶极矩的变化及峰值也随着激光强度的增强而增大. 对激光极化方向的研究发现,激光极化方向沿着CO分子轴向时,分子的电离最强且伸缩振动最剧烈. 当激光极化角增大时,CO分子的电离逐渐被抑制且电子的偶极振动对激光极化方向表现出较强的依赖性. 此外研究还表明,CO分子碳原子和氧原子周围电子的弥散方式不同且与激光极化方向有关. 关键词： 含时密度泛函理论 分子动力学 分子电离     

两种结构的C4分子在激光场中的响应

运用含时密度泛函理论和分子动力学相结合的方法,研究线形和环形C4分子的光吸收谱及在强激光场中的电子和离子响应.研究表明,在相同的激光参数下,线形C4分子主要是电子获得能量,而环形C4分子主要是离子获得能量;线形C4分子的电离增强,x方向的激光场仅激发起线形C4分子的Dx的偶极振动,但是能激发起环形C4分子Dx的偶极振动及Dy的非偶极振动.     

C4分子在激光场中的密度泛函理论研究

采用含时局域密度近似与分子动力学相结合的方法计算了C4分子的光学吸收谱及它在激光场中的响应.研究表明,在激光场中C4分子的诱导偶极矩与电离之间有着直接的联系,最外层电子对电离的贡献最大.此外,通过对激光的极化方向与C4分子的激发的关系的研究表明,x方向的激光场唯一的激发起C4分子x方向的偶极矩,电离增强而且离子的振动增强.     

C4分子在激光场中的密度泛函理论研究

采用含时局域密度近似与分子动力学相结合的方法计算了C4分子的光学吸收谱及它在激光场中的响应。研究表明,在激光场中C4分子的诱导偶极矩与电离之间有着直接的联系,最外层电子对电离的贡献最大。此外,通过对激光的极化方向与C4分子的激发的关系的研究表明,x方向的激光场唯一的激发起C4分子x方向的偶极矩,电离增强而且离子的振动增强。     

C_2H_2@C_(60)在飞秒激光作用下的分子动力学模拟

本文用含时密度泛函模拟了体系在外场为强激光场时的非线性光学性.并计算了C_2H_2@C_(60)和孤立C_2H_2分子在飞秒激光中分子的动力学过程,发现体系在脉冲激光作用的时间段内迅速电离,然后随时间演化也会发生持续的电离,这时的电离率不太高.在整个分子动力学过程中,可以观察到C_(60)内的小分子原子发生化学键的断裂和重组的行为,C_(60)结构在此过程中慢慢发生膨胀,最后分子键发生断裂,形成很多单电荷或者多电荷离子.同时发现体系被电离和解离的程度与激光的偏振方向有很大的关系.当激光偏振方向平行于分子轴时,分子发生共振的几率很大,能够产生丰富的碎片离子;垂直于分子轴时,共振的几率几乎为0,仅有母体离子出现.本文还发现当飞秒激光的偏振方向与分子轴平行时,能从氢化分子中有效提取H原子.     

极紫外阿秒脉冲在高次谐波产生过程中引起的非偶极效应

当红外强激光和极紫外(XUV)阿秒脉冲共同作用于原子分子时，电离出去的电子通常会吸收和辐射激光光子而发生能量扩展.讨论了由于XUV阿秒脉冲的短波长与扩展后的电子波包尺度可相比拟时在高次谐波产生过程中引起的非偶极效应.采用H⁺₂作为模型分子，并把分子轴置于激光场的传播方向，通过解二维含时薛定谔方程并比较考虑非偶极效应和采用偶极近似两种方法计算得到的结果，两者相比，前者的谐波强度降低，谐波频率向低级次稍有移动，电子能谱的能带内出现了更多的光电子峰.在相同的光电子能量处，两种方法计算得到的信号强度相差2—5倍.并且这种非偶极效应随着红外基频光光强的增大而增强，随阿秒脉冲波长的增大而减弱. 关键词： 非偶极效应 光场空间不均匀性 阿秒脉冲 高次谐波产生     

分子对飞秒激光场响应的含时密度泛函理论研究

采用含时密度泛函理论方法研究线性分子碳化锂(Li2C2)对飞秒激光场响应的电子-离子动力学行为.在典型的近共振和非共振的激光频率作用下,分别对比分析了分子的共振和非共振电离过程.研究发现:分子在共振频率激光场的作用下发生更强的电离过程,并倾向于发生库伦爆炸,键长的振荡断裂与电离相互促进影响,而分子在较弱的激光场作用下发生单光子电离过程;随着双脉冲时间间隔的增加,离化电子数在一定范围内呈振荡上升趋势,随后趋于常数.     

光强、频率对强激光场中的多原子分子离子增强电离行为的影响

通过利用短时指数传播子的对称分割和快速傅里叶变换,数值求解一维含时薛定谔方程,研究了一维多原子分子离子在超强脉冲强激光场中的增强电离(EI)行为,给出了激光强度和频率对增强电离的影响.计算表明随着激光频率的增加,增强电离的临界键长变小,电离概率 也减小;随着激光强度的增加,电离概率增加,当强度增加到一定值时,就不再出现增强电离现象. 关键词： 强激光场 分子离子 增强电离     

理论研究强激光场中2pz态氢原子的电离

运用强场近似速度规范理论研究了激发态氢原子的电离情况,当ω1a.u.,γ1时(ω是激光场的频率,γ是Keldysh绝热参数),在线性极化激光场中推导了2pz态氢原子电离率的简单表达式,从公式中可以看出在低频极限的情况下,电离率和激光场频率ω成正比,这一公式对激发态氢原子电离机制的研究提供了重要的理论参考.     

Tm:Y2SiO5晶体的生长和光谱性质研究

采用中频感应提拉法生长了高质量的Tm:Y₂SiO₅(Tm:YSO)晶体,测定了晶体的晶格常数和分凝系数.运用劳厄照相法确定了单斜晶系Tm:YSO晶体的三个偏振轴〈010〉,D₁和D₂,在室温下测量了三个偏振轴方向的吸收光谱、荧光光谱和荧光寿命,计算了晶体吸收峰的吸收线宽和吸收截面.研究发现,相对于其他两个偏振轴方向,D₁方向在790nm处出现较强的吸收峰, 关键词： 2SiO₅')" href="#">Tm:Y₂SiO₅ 单斜晶系 吸收光谱 荧光光谱     

Single crystal EPR spectrum of Cr3+ in lanthanum lutecium gallium garnet

The Cr³⁺ EPR spectra of YAG type crystals normally consist of four peaks whose positions are dependent on the axial zero-field splitting D with axis along a 111 direction and angle between that direction and the applied field H ₀. In LLGG only three principal peaks are observed with zero-field axis nearly along x, y or z. This anomaly is attributed to the relatively small size of Cr³⁺ compared to Lu³⁺ which it displaces in an octahedral site. D varies slightly for the different zero-field axes: 0.480 cm^–1 along x, 0.429 cm^–1 along y and 0.470 cm^–1 along z. The spectroscopic splitting factor g=1.978±0.001 is essentially isotropic and independent of axes within the experimental error.     

Dynamics of electronic and nuclear motion in a molecular hydrogen ion in a strong laser field

The dynamics of the electron and ion subsystems of a molecular hydrogen ion in the field of femtosecond titanium-sapphire laser radiation is investigated by using numerical simulation. The dependence of the probability of ionization and excitation of various electron states of H ₂ ⁺ on the radiation intensity and on the orientation of the molecule axis relative to the direction of polarization of the electric field of the wave is investigated. It is shown that the population of all electronic states of the molecule (except the ground state and the first excited state) is negligibly low in a wide range of radiation intensity. In such a situation, if the probability of system ionization is also low, the dynamics of vibration-rotation motion of nuclei in the molecule can be considered in the approximation of two potential surfaces (energy levels). The possibility of the effective orientation of the molecular axis along the direction of the electric field of the wave in the absence of dissociation of the system is considered.     

光子晶体微腔中高偏振单偶极模的研究

三角晶格排列的光子晶体微腔中的偶极模式是简并的,通过改变其晶格的对称性可以消除模式简并.晶格的整体形变破坏了晶格对称性从而影响光场的分布,同时还改变了电磁场的偏振分布.晶格整体形变使得简并的偶极模式分离成x极和y极偶极模式.通过计算分析发现分离后的模式具有良好的偏振特性,从而为实现单偏振光子晶体激光器提供了一种很好的途径.文中针对光子晶体薄板结构的微腔,主要计算了偶极模中x极偶极模式在不同拉伸时以及不同填充因子情况下的Q值,并分别计算了x关键词： 光子晶体 偶极模 品质因子 偏振度     

Acoustic wave propagation through the boundary between a liquid and the Heusler ferromagnetic alloy

Incidence of an acoustic wave upon a plane boundary between a liquid and a ferromagnetic crystal is considered. The ferromagnet is the Ni_2+x+y Mn_1−x Ga_1−y Heusler alloy with a shape memory, which is in the region of the premartensite or martensite phase transition in temperature. The directions of propagation and polarization and the amplitudes of the reflected and transmitted quasilongitudinal and quasitransverse waves in the (110) plane of the crystal are determined. Starting from a certain critical angle of incidence, a longitudinal wave in the crystal becomes inhomogeneous and gliding along the boundary with an accompanying surface oscillation. In the vicinity of the phase transition point, this wave may be radiated into the crystal bulk. Proceeding from the experimental data by Trivisonno for ultrasonic velocities and absorption in a Ni₂MnGa crystal, numerical estimates are obtained for the aforementioned acoustic effects.     

各向异性光反馈注入的垂直表面发射激光器的矢量偏振模转换机理

数值研究了各向异性光反馈注入的垂直表面发射激光器(VCSEL)的矢量偏振模转换机理,研究结果表明,首先,当注入电流接近阈值电流时,由VCSEL的外部参数和偏振器控制的光反馈注入量中各偏振模的能量决定VCSEL 输出的偏振态.其次,由偏振器控制的各向异性光反馈注入引起的VCSEL输出偏振态呈周期性变化.另外,当由偏振器控制的反馈注入量中的x^偏振和y^偏振模能量相当时, x^偏振模和y^偏振模之间竞争激烈,而激光器外部微小的扰动都会打破这两种偏振模竞争 关键词： 各向异性光反馈 垂直表面发射激光器 矢量偏振模     

Single and double ionization of the hydrogen molecule in an intense few-cycle laser pulse

In this paper, we present ab initio two-electron model calculations of laser-induced single and double ionization of the hydrogen molecule in a linearly polarized laser field with static nuclei located along the polarization axis. Within the model, the center-of-mass motion of the two electrons is restricted along the polarization axis of the field, while the relative electron motion is unrestricted. The results of numerical simulations allow us to identify and characterize the mechanisms leading to single and double ionization in an intense few-cycle laser pulse. The role of the rescattering mechanism on the ionization processes is analyzed in particular.     

The multielectron dissociative ionization dynamics of N2 molecule in intense femtosecond laser fields with arbitrary polarization

The field-ionization Coulomb explosion model is extended to investigate the multielectron dissociative ionization process of N₂ molecule irradiated by an intense femtosecond laser field with an arbitrary polarization. The ionization process of N₂ molecule is found to be optimal at the critical internuclear distance R_c=7a.u., which is independent of the laser polarization state, the molecular explosion channel and the angle between the molecular axis and the direction of laser electric field. The kinetic energies of the ion fragments are identical in the cases of linear and circular polarizations at the same incident laser intensity. However,the probability of electron ionization is very sensitive to the above three parameters. At the critical distance R_c=7a.u. the angular dependence of the threshold intensity for the over-the-barrier ionization leads to the geometric alignment of molecules in the case of linear polarization. The threshold intensity in the case of circular polarization is apparently higher than that in the case of linear polarization, which can well explain the significant decrease of ionization in the case of circular polarization. The numerical calculations are compared with the experimental measurements.