Stabilization of hydrogen atom in intense laser fields

The stabilization of real hydrogen atom rather than the model under the influence of high frequency superstrong laser pulse is investigated by numerical integration of time-dependent Schrödinger equation. The target wavefunctions are expanded in terms of a discrete L² basis. The evidence of stabilization as found by Su et al. for 1D model atom using the split operator technique has been confirmed for the hydrogen atom using L² technique.     

强激光场中真空极化效应

 通过求解狄拉克方程,对强激光场下真空极化问题进行了研究。理论计算结果表明：在仅随时间变化的电场下,要激发狄拉克海中负能级的电子,需要两个阈值条件,即激光场的电场强度大于等于10¹⁶ V/cm和激光场的持续时间大于等于10^-21 s。前者主要保证负能态电子有足够的能量跃迁到正能态,后者主要是保证电子在跃迁过程中动量亏损得以补偿。     

Sodium atom in strong magnetic fields：a pseudospectral approach

Energies and wavefunctions of low-lying states and Rydberg states for the sodium atom in uniform magnetic fields varying from 0 to 10^5T are calculated using a pseudospectral approach with a model potential in spherical coordinates. The energies are comparable with experimental results as well as those obtained by other calculations. The spectra of oscillator strength are worked out. The evolution of them with the magnetic field is shown.     

氦原子在啁啾激光与中红外组合场中产生的单个阿秒脉冲

通过Crank Nicolson方法数值求解一维氦原子的含时Schrdinger方程,研究了啁啾激光与中红外激光形成组合场驱动氦原子发射高次谐波的特点.研究结果表明,在组合场驱动下,高次谐波平台区能得到很大的扩展,其截至位置得到大幅度扩展,对平台区不同阶次范围的高次谐波进行叠加均能得到单个的阿秒脉冲,最短可实现46 as的单个脉冲输出,经分析发现,中红外场的加入,不仅使高次谐波的平台得到扩展,而且提高了平台区前端的谐波强度.通过经典计算和对电离几率特点的讨论,解释了发生这种现象的原因.     

强激光场中真空极化效应

通过求解狄拉克方程,对强激光场下真空极化问题进行了研究。理论计算结果表明：在仅随时间变化的电场下,要激发狄拉克海中负能级的电子,需要两个阈值条件,即激光场的电场强度大于等于1016 V/cm和激光场的持续时间大于等于10-21 s。前者主要保证负能态电子有足够的能量跃迁到正能态,后者主要是保证电子在跃迁过程中动量亏损得以补偿。     

少周期非均匀场下原子空间位置对高次谐波发射的影响

本文通过数值求解含时薛定谔方程,研究了少周期非均匀激光脉冲作用下氦原子选取不同的空间位置时高次谐波的发射情况.通过对原子在纳米结构空隙中心附近区域不同空间位置上的高次谐波发射情况的研究发现,非均匀激光场中,即使原子处在中心附近的很小的区域内,原子的空间位置也直接影响着高次谐波发射.随着空间内原子坐标的增大,高次谐波的截止得到扩展,且谐波平台区并非单向扩展,而是向两端同时的扩展.通过时频分析和半经典三步模型研究了高次谐波发射的物理机制,并对获得的物理现象给出合理的解释.     

The dissociation pathways of N2+ in intense femtosecond laser fields

Using a neutral N2 beam as target,this paper studies the dissociation of N2+ in intense femtosecond laser fields(45 fs,～1×10 16 W/cm 2) at the laser wavelength of 800 nm based on the time-of-flight mass spectra of N + fragment ions.The angular distributions of N+ and the laser power dependence of N + yielded from different dissociation pathways show that the dissociation mechanisms mainly proceed through the couplings between the metastable states(A,B and C) and the upper excited states of N2+.A coupling model of light-dressed potential energy curves of N+2 is used to interpret the kinetic energy release of N+.     

线型三原子分子在强激光场中多光子激发的李代数方法

使用二次非谐振子模型和Magnus近似方法构造了在强激光场下线型三原子分子的振动哈密顿并推导出时间演化算符的代数形式,在此基础上研究了线型DCN分子的跃迁几率随外场的频率和强度的变化关系,表明了多光子跃迁谱的特点.     

A simple non-perturbative approach of atom ionisation by intense and ultra-short laser pulses

A simple theoretical approach based on Coulomb-Volkov states is introduced to predict ionisation of atoms by intense laser pulses in cases where the effective interaction time does not exceed one or two optical cycles [M. Nisoli et al., Opt. Lett. 22, 522 (1997)]. Under these conditions, the energy distributions of ejected electrons predicted by this non-perturbative approach are in very good agreement with “exact" results obtained by a full numerical treatment. The agreement is all the better that the principal quantum number of the initial state is high. For very strong fields, most electrons are ejected at an energy which is close to the classical kinetic energy that would be transferred to free electrons by the electromagnetic field during the pulse. The power of the present approach appears when keV. In this region, full numerical treatments become very lengthy and finally do not converge. However, the present Coulomb-Volkov theory still makes reliable predictions in very short computer times. Received 19 November 1999 and Received in final form 19 January 2000     

超快强激光驱动的原子分子电离

强场电离是超快强激光与物质相互作用时发生的基本物理过程。强场驱动原子分子的电离电子动力学过程发生在一个光学振荡周期以内,是在阿秒时间尺度上研究电子超快动力学的典范。不仅如此,强场驱动下的超短电子束还为探测原子分子的结构及其超快动力学提供了重要的技术手段。文章首先简要阐述了超快强光场中原子分子电离的基本物理图像,在此基础上,介绍了近年来基于强场电离电子开展的超快过程研究的几个例子,最后简要讨论了强场电离研究的未来可能发展方向。     

高频强激光场中H-电离特性理论研究

高频强激光场中高价负离子（比如H-,H2-,He-,He2-等等）的稳定存在虽然在理论上早已得到得到证明,但在实验上至今没有被直接验证。为了探索可行的实验验证方案,通过以高频强场中的负一价氢离子H-为例,采用相空间平均法,详细研究了其在外加激光场中的电离率及光电子角分布情况。研究发现 的电离率比氢原子高,并且不存在氢原子在较强激光场中的电离抑制现象。另外随着激光场强度的增大和激光频率的减小,电子角分布与H-在高频场直接卸载后电子角分布的差别也增大。这些结果为将来在实验上验证高频强场中高价负离子的存在性提供了很好的理论依据。     

A new variational approach to the hydrogen atom in magnetic fields

We develop a simple and useful variational method to obtain approximate eigenenergies and expectation values ofr ² andρ ² for a hydrogenlike atom in a magnetic field. Results agree quite well with accurate numerically computed ones in the whole range of field intensities.     

基态分子波函数对N2分子在强激光场中产生高次谐波的影响

在强场近似下,利用简单的近似波函数作为分子基态最高占据轨道的波函数,研究了N₂分子在强激光场中产生高次谐波的特性,并将结果与用精确的分子波函数作为基态波函数得到的结果进行了比较.结果表明,采用这两种不同的分子基态波函数得到的高次谐波在分子轴与激光偏振方向间的夹角较小时符合得很好,而在夹角较大的情况下,两者的结果差异较大.通过分析不同波函数所给出的电子密度分布,给出了产生这种差异的原因. 关键词： 强激光场 强场近似 分子的高次谐波     

用缀饰原子法研究强激光场驱动下的共振荧光

本文用缀饰原子方法研究了单模激光场驱动下的两能级原子系统的共振荧光.通过在主方程中唯象地引入激光模的激发项补偿散射过程,使该模式中光子数减少.得到了主方程的定态解.并由此得到了共振荧光谱的强度分布及谱线形状.     

用伪谱方法研究强激光场中一维原子的稳定性

将伪谱方法推广应用到Kramers-Henneberger (KH) 坐标系中求解了一维原子在强激光场中的薛定谔方程,研究了强激光场中一维原子的稳定性.结果表明,在中等强度的激光场中,原子没有发生电离抑制,而在高频超强激光场中,原子的电离受到抑制.     

真实脉冲激光作用下的原子超阈值离化

在文献[18]的基础上进一步讨论真实脉冲激光作用下的原子超阈值离化,在考虑了初始离化时刻的影响后,结果清楚地表明,随激光脉宽减小而产生峰红移,以及同时出现的离化电子谱峰的增宽现象.     

一维μ介子模型原子的超强场高次谐波发射

本文提出了一个一维μ介子原子模型,用数值积分方法求解了在超强激光场作用下该模型原子的含时Schrdinger方程,得到了它的高次谐波发射谱.该谱表明,借助于这一奇异原子模型,可将相干辐射由XUV波段推向γ-射线波段.针对这个体系的高次谐波发射效率低的缺点,引入双色场后使发射效率提高了两个数量级.     

Single and multiple ionization of N2 molecules by intense light fields of femtosecond duration

We report studies on the multiple ionization of the N₂ molecule using intense, femtosecond laser pulses. We present details of the experimental characterisation of the light pulses and analysis and detection of the ions produced. Precautions to be taken in intense field ionization experiments are discussed. We illustrate the retrieval of information about different aspects of the ionization process (such as, kinetic energies of the fragments produced, dissociation bond lengths and information on the precursors to fragmentation) using coincidence techniques. We report results of the first measurements of the angular distribution of a highly charged fragment, N³⁺.