H2+和HD+分子体系高次谐波发射效率的理论研究

本文通过求解一维含时薛定谔方程, 比较研究了H2+和HD+分子离子体系的高次谐波发射效率. 数值计算结果表明, 在相同激光条件下, 不对称分子体系能产生更高强度的谐波谱. 此外, 借助时频分布, 电离几率和电子-核波包密度概率分布图, 对计算结果做出了合理的解释.     

H_2~+和HD~+分子离子体系高次谐波发射效率的理论研究

本文通过求解一维含时薛定谔方程,比较研究了H2+和HD+分子离子体系的高次谐波发射效率.数值计算结果表明,在相同激光条件下,不对称分子体系能产生更高强度的谐波谱.此外,借助时频分布,电离几率和电子-核波包密度概率分布图,对计算结果做出了合理的解释.     

利用高次谐波实现分子的轨道成像：两中心干涉效应

分子的轨道成像是科学研究中广为关注的主题。能否利用高次谐波来追踪化学反应的具体过程具有重要的实践意义,此外研究分子的轨道成像的理论基础还能够深化人们对原子的和分子的高次谐波辐射机制的理解。文章在简要回顾高次谐波研究历史的基础上,介绍了文章作者近期在利用高次谐波实现分子的轨道成像中的工作。文章作者通过数值地和解析地研究分子的高次谐波辐射的取向依赖检验了分子轨道成像的基本假设。研究显示,由于两中心干涉效应,高次谐波辐射过程中的分子的再碰撞电子波包与分子的价电子轨道的对称性和电离能密切相关。作为一个结果,分子的再碰撞电子波包的谱振幅可能和它的参考原子的再碰撞电子波包的谱振幅在某些能量区域显示很大的差别。这个发现对分子的轨道成像实验具有重要的意义。     

利用43飞秒的强激光脉冲实现单个阿秒脉冲输出的新机理

研究了多个光周期的长脉冲(43 fs)激光与氖原子相互作用产生的高次谐波的辐射特性. 通过计算机数值模拟，发现当激光场的强度超过饱和光强时，原子将会在几个光周期内被迅速电离，使得原子的高次谐波谱在截止区呈现出平滑的多平台结构. 同时，在高频波段离子产生的高次谐波的影响将变得十分显著. 通过选取合适的子平台进行频率叠加，在消除了离子的高次谐波的影响后，可以获得单个的阿秒软X射线脉冲. 关键词： 高次谐波 阿秒脉冲     

电子与D2分子的相关量子动力学的理论研究

文章利用含时波包方法，通过求解三维电子与核运动相关的薛定谔方程得到了D^＋离子的动能分布，同时电子被电离后多次返回与D2^＋离子发生碰撞的儿率也得到了计算，并发现D^＋离子主要来源于电子与D2^＋离子在各个波长第一个光周期内的第一次碰撞，我们的计算结果不但与实验符合较好，而且给出了在阿秒时间分辨率下追踪电子与核相关运动的量子动力学方法。     

超强激光场中氢原子辐射高次谐波蒙特卡罗模拟

运用蒙特卡罗方法，模拟和计算出在超强激光场中，氢原子在相对论领域的电离几率和辐射出的高次谐波，并且讨论了氢原子的电离几率和辐射出的高次谐波与激光场的电场和磁场的关系。     

低温等离子体中H_2(D_2和T_2)的振动分布

在边界等离子体中,氢分子具有相当高的密度,这些分子与等离子体发生碰撞可使氢分子的振动分布发生变化.本文讨论氢分子的行为,采用了最新的截面数据,对于文献中尚无可利用的截面,运用半经典的Gryzinski方法进行计算.基于准静态近似和准稳态碰撞辐射模型对氢及其同位素分子D2和T2的振动分布进行了研究.结果表明:当电子温度低于10 eV时,氢及其同位素分子的振动分布在较低的振动能级随着电子温度的升高而减小;而在较高的振动能级,分布则呈现相反趋势.     

氢分子离子的两个核对谐波贡献的研究

通过求解含时薛定谔方程的方法研究H2+的两个核分别对高次谐波产生的贡献. 结果表明,在激光场的作用下两个核周围的电子分布不同从而导致了在不同时刻两个核对谐波产生的贡献不同,即在半整数个光周期谐波的产生主要由核1贡献而在整数个光周期主要由核2贡献. 然后结合时频分布图和电子和核波包密度图,对其物理机制进行了合理解释.     

电子与氢及其同位素分子碰撞的非解离性电离截面研究

在边界等离子体中, 氢及其同位素分子与高能电子碰撞可发生电离反应. 对于尚无可利用的氢及其同位素分子的电子碰撞非解离性电离反应截面, 基于莫尔斯函数、弗兰克-康登原理, 采用半经典的Gryzinski方法进行了计算. 得到反应截面随电子能量的变化情况以及振动能级对反应截面的影响. 计算结果表明分子的振动激发对电离反应有着显著影响.     

圆偏振激光脉冲附加静电场或太赫兹场时H2+高次谐波产生

本文通过数值求解二维含时薛定谔方程理论的研究了圆偏振激光脉冲(circularly polarized laser pulse, CPLP)作用下H2+的高次谐波产生(high-order harmonic generation, HHG)。通过对比CPLP附加静电场和CPLP附加太赫兹场(terahertz, THz)时的高次谐波发射谱发现,当在CPLP的方向附加静电场时,谐波谱出现双平台结构,且布满调制,通过电子波包概率分布图像发现,电子三次与母核复合,量子轨道之间产生了较严重的干涉。当附加相同强度的THz场时,电子仅两次与母核复合,量子轨道之间的干涉减少,最终得到了86eV到208eV带宽为122eV的连续谱,相比于附加静电场,谐波谱变得连续且平滑,实现了量子轨道调控。最后,利用半经典三步模型、时频分析和电离几率等对谐波发射物理机制进行了深入研究。     

Rotational-coherence molecular laser isotope separation

We have proposed a laser isotope separation method, utilizing rotational coherence of a simple molecule. In the scheme, photoexcited molecules are isotopically separated by difference of rotational period between them. To illustrate this method, two-pulse photodissociation of mixed ⁷⁹Br₂/⁸¹Br₂ isotopes has been investigated theoretically. The photodissociation probabilities of ⁷⁹Br₂ and ⁸¹Br₂ have been calculated as functions of time delay between the photoexcitation and dissociation laser pulses. We have demonstrated that isotope enrichment factor of ⁷⁹Br relative to ⁸¹Br can be changed from 0.34 to 1.8, by simply changing the time delay only by 0.2 ns. Additionally, we have shown that this method is effective for heavy isotopes, based on mass dependence of the isotope enrichment factor.     

Correlation quantum dynamics between an electron and D+2 molecule with attosecond resolution

Recently, Niikura et al. [Nature (London) 421, 826 (2003)] have applied the entanglement approach to exploit the correlation between the electronic and nuclear wave packets. Here, we use the time-dependent-wave-packet method to calculate the kinetic energy distribution of the D+ ion resulting from the recollision between an electron and its parent ion D+2(X2Sigma+g) within the attoseconds time scale. Our theoretical results of the D+ ion kinetic energy spectra accord well with the experimental ones, and the recollision probabilities between the electron and the D+2 molecule have been calculated.     

Interaction of intense beams of highly vibrationally excited molecules with molecules (clusters) condensed on a cold surface

The interaction of intense beams of SF₆ and CF₃I molecules, excited by powerful IR laser radiation to high vibrational states (0.3 eV ≤ E _vib ≤ 2.0 eV), with molecules (clusters) condensed on a cold surface (T _s ≈ 80–85 K) has been studied. The probability that the excited and unexcited molecules are reflected from the cold metal surface covered by condensed molecules (clusters), as well as the probability that such excited and unexcited molecules are transmitted through a cooled multichannel metal plate and a converging cone oriented at an angle relative to the molecular beam axis, has been determined. Expressions for these probabilities of reflection and transmission as functions of the angle of incidence and the parameters of the exciting laser radiation and the molecular beam are obtained. It is shown that highly vibrationally excited molecules are reflected from the surface and transmitted through the plates and cones with a much higher probability than unexcited molecules. The results suggest that this phenomenon can be used for the separation of molecules in a beam with respect to isotope (or atomic) composition.     

Hyperfine structure and isotope shifts in the 5d6s2 a2D3/2--5d6s(a3D)6p z4F5/2 ° transition of Hf II

The hyperfine structure and isotope shifts of the transition between the 5d6s² a²D_3/2 ground state and the 5d6s(a³D)6p z⁴F_5/2 ^° excited state of singly ionized hafnium at \lambda=340 nm have been investigated by laser spectroscopy using a radio-frequency quadrupole ion trap. The magnetic dipole coupling constant A and electric quadrupole coupling constant B of the two atomic levels for both stable isotopes ¹⁷⁷Hf and ¹⁷⁹Hf are determined. The changes of mean square nuclear charge radii \delta[ r²] of the stable Hf isotopes and the radioactive isotope ¹⁷²Hf (T_1/2=1.87a) have been extracted from the data. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electron wavepacket phases in ionization and rescattering processes by intense laser pulses

Exact numerical solutions of the time-dependent Schrödinger equation, TDSE, are presented for the H atom and H^2/+ molecular ion ionized by short (10 optical cycles), intense I ₀ ≥ 10¹⁴ W/cm², 800 nm laser pulses. Calculations of the time dependent expectation values of the dipole moment d(t), velocity $ \dot d Exact numerical solutions of the time-dependent Schr?dinger equation, TDSE, are presented for the H atom and H^2/+ molecular ion ionized by short (10 optical cycles), intense I ₀ ≥ 10¹⁴ W/cm², 800 nm laser pulses. Calculations of the time dependent expectation values of the dipole moment d(t), velocity (t), and acceleration (t) are used to identify the phase of these physical parameters with respect to the laser field during the harmonic generation process. It is found in general that electron wavepackets in an inner region near the parent ion are out of phase with the response expected from the classical laser induced recollision model, whereas wavepackets in an outer region, far from the parent ion, are in phase with the field force. It is found furthermore that it is the inner electron wavepacket which contributes mainly to the high order harmonic generation, HHG, process, even though its acceleration is out of phase with the field force. This suggests strong Coulomb refocussing effects in the HHG process, especially in the case of H^2/+. Original Russian Text ? Astro, Ltd., 2009. In honor of Prof. N.B. Delone. The article is published in the original.     

Dissociation of molecular hydrogen ions by an IR laser pulse

Dissociation dynamics of the simplest molecular systems, such as H₂ ⁺, D₂ ⁺ and HD⁺ ions, in an intense IR laser field has been investigated by numerical modeling. An n-term approximation has been developed to describe the molecular system dynamics in an intense electromagnetic field. Calculations by the n-term approximation have been compared to an accurate numerical solution of the two-particle problem. The dissociation probability as a function of the frequency and intensity of radiation for different isotopes in a molecular hydrogen ion is discussed. A quasistatic model of molecule dissociation in an IR field has been suggested, and limits of its applicability have been determined. Zh. éksp. Teor. Fiz. 113, 128–143 (January 1998)     

Hyperfine structure and isotope shift of the neutron-rich barium isotopes139–146Ba and148Ba

The hyperfme structure and isotope shift in the 6s ² S _1/2?6p ²P_3/2 line of Ba II (455.4 nm) have been measured by collinear fast-beam laser spectroscopy for the neutron-rich isotopes^139–146Ba and¹⁴⁸Ba. Nuclear moments and mean square charge radii of these isotopes have been recalculated. The isotope shift of the isotope¹⁴⁸Ba (T_1/2=0.64 s) could be studied for the first time, yieldingδ〈r²〉^138,148=1.245(3) fm².     

Optical emission studies of sulphur plasma using laser induced breakdown spectroscopy

We present the optical emission studies of sulphur (S) plasma generated by the first (1064 nm) and second (532 nm) wavelengths of a Q-switched Nd:YAG laser. The target material was placed in front of laser beam in air at atmospheric pressure. The experimentally observed line profiles of neutral sulphur have been used to extract the electron temperature (T _e ) using the Boltzmann plot method, whereas the electron number density (N _e ) has been determined from the Stark broadening. The electron temperature is calculated by varying, distance from, the target surface along the line of propagation of plasma plume and also by varying the laser irradiance. Beside we have studied the variation of number density as a function of laser irradiance as well as its variation with distance from the target surface. It is observed that electron temperature and electron number density increases as laser irradiance is increased.     

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}     

Predictions for cross sections of light proton-rich isotopes in the ~(40)Ca + ~9Be reaction

The cross sections for Z=10–19 with isotopes T_z=-3/2 to-5 in the 140A Me V~(40)Ca+~9Be projectile fragmentation reaction have been predicted.An empirical formula based on the correlation between the cross section and average binding energy of an isotope has been adopted to predict the cross section.The binding energies in the AME16,WS4,and the theoretical prediction by the spherical relativistic continuum Hartree-Bogoliubov theory have been used.Meanwhile,the fracs parametrization and the modified statistical abrasion-ablation model are also used to predict the cross sections for the proton-rich isotopes.The predicted cross sections for the T_z=-3 isotopes are close to 10~(-10)mb,which hopefully can be studied experimentally.In addition,based on the predicted cross sections,Z=14 is suggested to be a new magic number in the light proton-rich nuclei with T_z-3/2,for which the phenomenon is much more evident than it is from the average binding energy per nucleon.