分子核间距对非时序双电离的影响

利用半经典再散射模型研究了激光强度在一定范围内时分子核间距对非时序双电离过程的影响.分别计算了非时序双电离率、两电子的电离能、两电子的动量相关、Coulomb和激光场的复合势随分子核间距的变化关系.研究表明,分子核间距在1.0—6.0 a.u.范围内时,非时序双电离率和两电子动量和为零的双电离事件数随着分子核间距的增大而增大.当分子核间距继续增大(大于6.0 a.u.)时,非时序双电离率和两电子动量和为零的双电离事件数却减小.     

分子双电离对激光偏振性的依赖关系

利用经典系综模型研究了氢分子双电离对激光场椭圆率的依赖性.研究发现,氢分子双电离机制对激光的椭偏性有强烈的依赖关系.随着激光场椭圆率的增加,双电离机制由非次序双电离转变为次序双电离.在大椭圆率情况的次序双电离中,电子关联动量分布随椭圆率的灵敏变化显示了电子出射时间对椭圆率的强烈依赖关系.     

双色强激光中原子电离率与相位关系的数值研究

用Kulander等人发展的方法计算了双色光电离率随φ的变化,发现了当双色光场强度超过阈值时R-φ关系的转变,与经典方法计算的结果作了比较。     

碰撞阈值下氩原子非次序双电离

利用三维经典系综模型研究了碰撞阈值下氩原子的非次序双电离.计算结果表明,关联电子末态纵向动量主要分布在二、四象限,且在原点附近几乎没有分布;Ar²⁺离子末态纵向动量谱在零动量附近呈单峰结构.上述结果与实验结果 定量一致.轨迹分析表明,在碰撞阈值下,氩原子非次序双电离的微观物理机理在不同激光强度下是不相同的.当激光强度I=0.7×10¹⁴ W/cm²时,一次碰撞主导重碰撞过程.而当I=0.4×10^{14关键词： 非次序双电离 库仑引力 碰撞阈值 电子关联}     

氦原子非次序双电离对正交双色场强度比的依赖关系

利用经典系综模型研究了正交双色场中氦原子非次序双电离对双色场强度比的依赖关系.研究表明, 该依赖关系与双色场相对相位φ 有关. φ =0.25π 时,沿长波长激光偏振方向的相关动量谱随强度比的增大从相关模式转变为反相关模式. φ =0.35π, 0.45π 时,相关动量主要分布在第一和第三象限,相关模式几乎不随强度比的变化而变化.对双电离轨迹碰撞时间、碰撞角、碰撞动量的向后分析可以解释上述结果,并显示了正交双色场对非次序双电离中碰撞时间、碰撞角的控制作用.     

正交双色场中氢分子非次序双电离的研究

利用经典系综模型,研究了正交双色场作用下氢分子非次序双电离中双电离电子的相关特性.结果表明,双电离电子相关动量谱强烈地依赖于正交双色场的相对相位.通过改变正交双色场的相对相位,相关动量可以从反相关模式转变为相关模式.向后分析表明,相关电子动量谱对双色场相对相位的依赖关系起源于碰撞过程中碰撞电子碰撞角和碰撞动量对相对相位...     

H$lt;sub$gt;2$lt;/sub$gt;$lt;sup$gt;+$lt;/sup$gt;在强激光场中的解离及其量子调控的理论研究

利用非波恩-奥本海默近似的三维含时量子波包法,理论研究了氢分子离子在强激光场中的解离动力学.通过分析H₂⁺在不同的初始振动态（ν=0–9）和激光场强度下的解离核动能谱,得到了H₂⁺的光解离机理及其随激光场的变化规律.研究结果表明：当激光场的强度I₁=5.0×10¹³ W/cm²时,分子的解离来源于高振动态ν=5–9,其解离机理主要是通过键软化、键硬化和阈下解离过程.当激光场的强度I₂=1.0×10¹⁴ W/cm² 时,H₂⁺在低振动态ν=3–4上的阈上解离起主导作用,而高振动态的键软化、键硬化和阈下解离所占的比重明显地下降了.研究结果为后续的量子调控的实验研究提供了科学的理论预测和指导. 关键词： 光解离 氢分子离子 含时波包法 核动能谱     

双色场诱导气体产生相干可控的四次谐波

利用钛宝石飞秒激光器输出的基频脉冲ω及其倍频脉冲2ω所构成双色场作用空气, 实验中检测到了中心波长处于真空紫外波段的四阶谐波. 在气体未发生电离的情况下, 四次谐波强度对双色场的能力依赖关系显示其产生是参量过程2ω+ω+ω→4ω的贡献. 当气体发生电离, 四次谐波强度与双色场相对相位有关, 可通过双色场相干控制. 实验研究了四次谐波对双色场相位的依赖性以及与太赫兹波的关联性, 其结果与数值模拟结果相符, 分析发现当气体发生电离时四次谐波的产生过程存在太赫兹辐射Ω_THz的参与, 是参量过程2ω+2ω±Ω_THz→4ω和2ω+ω+ω→4ω的共同贡献.     

基态MgB2分子的结构与分析势能函数

应用群论及原子分子反应静力学方法推导MgB₂分子的电子状态及其离解极限,采用密度泛函B3LYP和从头计算QCISD方法在6-311++G**基组水平上,对MgB₂分子可能的状态进行优化计算,得出MgB₂的三重态能量最低,其稳定构型为C_2v,平衡核间距R_e=2.2977,键角α_BMgB=41.5521°,能量为-248.9645a.u.同时还计算了基态的简正振动频率:对称伸缩振动频率ν（B₂）=315.4430 cm^-1,反对称伸缩振动频率ν（A₁）=418.1883 cm^-1和弯曲振动频率ν（A₁）=968.9672 cm^-1.在此基础上,使用多体项展式理论方法,导出了基态MgB₂分子的解析势能函数,其等势面准确再现了基态MgB₂平衡结构和离解能,并由此讨论了B+MgB和Mg+BB分子反应的势能面静态特征. 关键词： 2')" href="#">MgB₂ 多体项展式理论 解析势能函数     

双色噪声驱动光学双稳系统的弛豫时间研究

研究乘性及加性噪声的自关联时间τ₁和τ₂,交叉关联时间τ对光学双稳系统的弛豫时间的影响.弛豫时间T由Mei等所采用的方法得到. 经数值计算, 结果表明: 两噪声间交叉关联时间τ及乘性噪声的自关联时间τ₁延缓系统涨落的消退(T随τ及τ₁的增大而增大);T随加性噪声的自关联时间τ 关键词： 关联噪声 弛豫时间 光学双稳系统     

Nonsequential double ionization of diatomic molecules by elliptically polarized laser pulses

Using the classical ensemble method, we investigate nonsequential double ionization （NSDI） of diatomic molecules by elliptically polarized laser pulses. The results show that the ellipticity of the laser field has a strong suppression effect on NSDI probabilities both in parallel and perpendicular alignments. The double ionization （DI） channel is commonly dominated by NSDI, and the NSDI channel changes with ellipticity. As ellipticity increases, more and more NSDIs occur through recollision excitation with subsequent field ionization （RESI）. Moreover, like the case of linear polarization, the two electrons involved in NSDI for perpendicularly aligned molecules are more likely to emit into the opposite hemispheres as compared to the case of parallel alignment. Additionally, this alignment effect increases as ellipticity increases.     

Nonsequential double ionization of nonaligned diatomic molecules N2 and O2

Nonsequential double ionization (NSDI) processes of nonaligned diatomic molecules N2 and O2 are studied using the S-matrix theory. Our results show that the NSDI process significantly depends on the molecular symmetry and structure. The ratio of NSDI rate to single ionization rate as a function of the field intensity is obtained. It is found that N2 behaves closely with its companion atom Ar in the ratios over the entire intensity range, while O2 exhibits an obvious suppression effect, which is qualitatively consistent with the experiment.     

低强度周期量级脉冲驱动排列分子的非次序双电离

本文利用三维经典系综模型研究了低强度周期量级脉冲驱动排列分子的非次序双电离. 结果表明, 电子对的关联特性强烈地依赖于分子的排列方向和激光脉冲的载波包络相位; 垂直分子反关联电子对的比例总是高于平行分子反关联电子对的比例; 当载波包络相位从0到π 逐渐增加时, 反关联电子对的数目先增加再减少; 对于平行分子, 电子对的释放总是以正关联为主; 而垂直分子的主导关联模式则依赖于激光脉冲的载波包络相位, 当载波包络相位为0.3π-0.7π之间时, 电子对以反关联释放为主, 其他相位下以正关联为主. 本文利用分子势能曲线和电子返回能量很好地解释了电子关联特性对分子排列方向和载波包络相位的依赖关系.     

异核双原子和三原子分子在红外强激光场中的电离抑制

Ionization is the fundamental process in interaction of atoms/molecules with femtosecond strong laser fields. Comparing to atoms, molecules exhibit peculiar behaviors in strong-field ionization because of their diverse geometric structures, molecular electronic orbitals as well as extra nuclear degrees of freedom. In this study, we investigate strong field single and double ionization of carbon monoxide (CO) and carbon dioxide (CO₂) in linearly polarized 50-fs, 800-nm laser fields with peak intensity in the range of 2×10¹³ W/cm² to 2×10¹⁴ W/cm² using time-of-flight mass spectrometer. By comparing the ionization yields with that of the companion atom krypton (Kr), which has similar ionization potential to the molecules, we investigate the effect of molecular electronic orbitals on the strong-field ionization. The results show that comparing to Kr, no significant suppression is observed in single ionization of both molecules and in non-sequential double ionization (NSDI) of CO, while the NSDI probability of CO₂ is strongly suppressed. Based on our results and previous studies on homonuclear diatomic molecules (N₂ and O₂), the mechanism of different suppression effect is discussed. It is indicated that the different structure of the highest occupied molecular orbitals of CO and CO₂ leads to distinct behaviors in two-center interference by the electronic wave-packet and angular distributions of the ionized electrons, resulting in different suppression effect in strong-field ionization.     

Two-color resonance photoionization spectrum of nickelocene in a supersonic jet

Two-color photoionization of nickelocene molecules cooled in a supersonic jet is performed using a tunable nanosecond pulsed laser. The first stage of the multiphoton excitation is the transition from the highest occupied molecular orbital of nickelocene to the lowest Rydberg level. Conditions are found under which molecular ions (η ⁵-C₅H₅)₂Ni⁺ are the only product of the multiphoton ionization in the one-color experiment. Irradiation of an excited molecule by an intense pulse of another laser increases significantly the yield of molecular ions. The dependence of the yield of (η⁵-C₅H₅)₂Ni⁺ ions on the frequency of the second laser makes it possible to determine the adiabatic ionization potential of nickelocene as 6.138±0.012eV.     

Capture of an electron by ions in methionine and norleucine molecules

The relative cross sections of processes taking place when H⁺ and He²⁺ ions with an energy of 6z keV (z is the ionic charge) capture an electron from molecules of C₅H₁₁NO₂S methionine (proteogenic amino acid) and C₆H₁₃NO₂ norleucine (nonproteogenic amino acid) are measured by time-of-flight mass spectrometry (a methionine molecule transforms into a norleucine molecule by substituting the CH₂ group for the S heteroatom). The fragmentation pattern of resulting molecular ions is established from correlation analysis of the detection times of all fragment ions. The results are compared with experimental data for fragmentation of the same molecules ionized by electrons and photons. In these amino acids, the pattern of molecular ion fragmentation is found to depend on the type of molecule ionization. However, the detachment cross section of the COOH neutral group or residue (neutral or charged) R of a side chain of the amino acid is invariably among the largest. The relative cross sections of capture with single and double ionization of molecules are measured.     

Electron‐Nuclear Dynamics in Molecular Harmonic Generation Driven by a Plasmonic Nonhomogeneous Field

Electron (z)‐nuclear (R) dynamics in the molecular high‐order harmonic generation (MHHG) from H₂⁺ driven by the plasmonic nonhomogeneous field, generated by the surface plasmon polaritons in the bowtie‐shaped nanostructure, have been theoretically investigated through solving the two dimensional time‐dependent Schrödinger equation with the Non‐Bohn‐Oppenheimer approximation. It is found that (i) due to the plasmonic enhancement of the laser intensity, the harmonic cutoff can be extended when the spatial position of H₂⁺ is away from the gap center of the nanostructure. However, due to the limit of the gap size, the threshold value of the harmonic cutoff can be obtained at a given position of H₂⁺. (ii) Due to the asymmetric enhancement of the laser intensity in space, the extended higher harmonics are respectively from E(t) > 0 a.u. or E(t) < 0 a.u. for the cases of the positive and the negative spatial position of H₂⁺. As a result, the intensities of the extended higher harmonics are different and can be controlled by changing the carrier‐envelope phase and the pulse duration of the laser field. (iii) In the few‐cycle pulse duration, the MHHG mainly comes from the multi‐photon resonance ionization (MPRI), while as the pulse duration increases, the MPRI, the charge‐resonance enhanced ionization (CREI) and even the dissociative ionization (DI) are contributed to the MHHG. Moreover, as the spatial position of H₂⁺ moves, the contributions of the MHHG from the MPRI, the CERI and the DI can be controlled. (iv) The contributions of the MHHG from the two‐H nuclei have been investigated and found that when E(t) > 0 a.u., the intensities of the harmonics from the negative‐H is higher than those from the positive‐H; while when E(t) < 0 a.u., the intensities of the harmonics from the positive‐H plays the main role in the MHHG. Moreover, the multi‐minima, caused by the two‐center interference can also be found. (v) Finally, by superposing a properly selected harmonics, a single isolated attosecond pulse (SIAP) with the full width at half maximum (FWHM) of 34 as can be obtained.     

用CARS技术确定拉曼退偏比的一种数据处理新方法

Yuika等人利用偏振CARS技术可以准确地确定分子的拉曼退偏比.其方法是，首先对不同检偏角_d所对应CARS谱峰的频率分布进行数学模拟，然后由所得系数随检偏角φ_d的变化求得使CARS信号中共振项消失的偏振角φ^０_d，最后由消失条件ρ＝-1/(tanθtanφ⁰_d)求出退偏比ρ，θ为产生CARS光的Pump光与Stokes光偏振方向的夹角.本文提出的数据处理方法，即交点法.同Yuika等人处理数据的方法相比，交点法毋需关于谱峰频率分布的知识，做法也更为简便.