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A method is proposed for the calculation of the S matrix for many-electron processes in intense-laser atom physics, in close analogy to the strong-field approximation for one-electron processes. Given a scenario of how some process evolves, corresponding approximations to the classical action are made which allow for the evaluation of the quantum-mechanical S matrix. The method is applied to the distribution of the total electronic momentum in nonsequential double ionization, and the results are compared to recent measurements. Good agreement is obtained for neon for a rescattering scenario. There is no comparable agreement for helium and argon, and possible alternative scenarios are discussed. 相似文献
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利用三维经典系综模型系统地研究了不同强度线偏振激光脉冲驱动下He原子的非次序双电离.结果表明在非次序双电离中回碰电子的返回次数、两电子的碰撞距离和电子对的关联特性都强烈地依赖于激光强度.对于750 nm,随着激光强度的增加,单次返回诱导的非次序双电离事件逐渐减少,而多次返回事件的比例显著增加.对于1500 nm,随着激光强度的增加,前三次返回诱导的非次序双电离事件都会减少,返回次数大于3的轨道对非次序双电离的贡献逐渐增加.这是因为在高强度下每次返回过程中母核的库仑吸引对返回电子横向偏离的补偿较弱,所以需要更多次的返回来补偿电子的横向偏离以实现再碰撞.轨道分析表明非次序双电离中两电子的碰撞距离随激光波长和强度的增加而逐渐减小.最后讨论了非次序双电离中电子对的关联特性对返回次数的依赖. 相似文献
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We use classical simulations to analyze the dynamics of nonsequential double-electron short-pulse photoionization. We utilize a microcanonical ensemble of 10(5) two-electron "trajectories," a number large enough to provide large subensembles and even sub-subensembles associated with double ionization. We focus on key events in the final doubly ionized subensemble and back-analyze the subensemble's history, revealing a classical slow-down scenario for nonsequential double ionization. We analyze the dynamics of these slow-down collisions and find that a good phase match between the motions of the electrons can lead to very effective energy transfer, followed by escape over a suppressed barrier. 相似文献
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Electron correlation is encoded directly in the distribution of the energetic electrons produced in a recollision-impact double ionization process, and varies with the laser field and the target atoms. In order to get equivalent electron correlation effects, one should enlarge the laser intensity cubically and the laser frequency linearly in proportion to the second ionization potentials of the target atoms. The physical mechanism behind the transform is to keep the ponderomotive parameter unchanged when the laser frequency is enlarged. 相似文献
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Parker JS Doherty BJ Taylor KT Schultz KD Blaga CI DiMauro LF 《Physical review letters》2006,96(13):133001
Electron energy distributions of singly and doubly ionized helium in an intense 390 nm laser field have been measured at two intensities (0.8 PW/cm2 and 1.1 PW/cm2, where PW is defined as 10(15) W/cm2). Numerical solutions of the full-dimensional time-dependent helium Schr?dinger equation show excellent agreement with the experimental measurements. The high-energy portion of the two-electron energy distributions reveals an unexpected 5U(p) cutoff for the double ionization (DI) process and leads to a proposed model for DI below the quasiclassical threshold. 相似文献
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Multiple recollisions in nonsequential double ionization below the recollision-ionization threshold 下载免费PDF全文
Xiao-Meng Ma 《中国物理 B》2021,30(12):123402-123402
By using the three-dimensional classical ensemble model, the recollision dynamics in nonsequential double ionization (NSDI) of Ar by 780-nm laser pulses at (6-1.2)×1014 W/cm2 was extensively studied. We revealed the picture of multiple-recollision in the double ionization events at the laser intensity region below the recollision-ionization threshold. Via tracing the NSDI trajectories, it was found that the contribution of these multiple-recollision events increases as the laser intensity decreases. In this low intensity region, many multiple-recollision induced NSDI trajectories occur through the doubly excited states. The decay speed of the doubly excited state decreases with the decreasing laser intensity. 相似文献
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通过数值求解薛定谔方程并用“抓拍”(snapshot)的方式观测两电子动量分布,我们研究了超强超快激光场中原子发生非次序双电离的不同机制。我们的模拟表明“抓拍”过程中双电离波函数的选取范围对两电子动量分布图样的特征和分布范围等都有显著的影响。图样中这种由于不同的观测范围导致的明显区别直接地影响我们对非次序双电离动力学过程的分辨。为此本文即结合经典再散射三步模型,详细分析了“抓拍”过程中双电离波函数范围的选取,并深入讨论了不同的非次序双电离机制及其对应的动量分布的特征。本文的结果将给相关的实验研究提供有益的参考。 相似文献
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利用三维经典系综模型研究了氢分子非次序双电离对核间距的依赖性.在不同分子取向下,氢分子双电离率随核间距的增大而先增大后减小,在核间距为4a.u.时取最大值.氢分子非次序双电离对核间距的依赖性随分子轴与激光偏振方向间夹角φ的增大而减弱.φ=0时,氢分子非次序双电离包含丰富的相关模式,对核间距有强烈的依赖性φ=π/2时,不同核间距下的相关模式相似,重碰撞在双电离过程中发挥更重要的作用.这些结果表明分子结构对双原子分子非次序双电离有重要影响.
关键词:
非次序双电离
核间距
关联动量分布 相似文献
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We study the double ionization process of atoms in intense laser fields. The momentum distributions of the correlated electrons are calculated. Contrary to the general expectation, we show an increasing proportion of the electrons ionized via excitation with the increasing laser intensity. These electrons generally have small energy thus they concentratedly distribute on the central region of the momentum diagram. Consequently, the central part of the momentum diagram becomes more notable in higher intensity laser fields. Further study suggests that this phenomenon is general in double ionization. 相似文献
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A classical ensemble method is used to investigate nonsequential double ionization(NSDI) of Ar atoms irradiated by linearly polarized few-cycle laser pulses. The correlated-electron momentum distribution(CMD) exhibits a strong dependence on the carrier-envelope phase(CEP). When the pulse duration is four cycles, the CMD shows a cross-like structure, which is consistent with experimental results. The CEP dependence is more notable when the laser pulse duration is decreased to two cycles and a special L-shaped structure appears in CMD. Recollision time of returning electrons greatly depends on CEP, which plays a significant role in accounting for the appearance of this structure. 相似文献
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利用经典系综模型研究了椭圆偏振激光脉冲驱动的氩原子非次序双电离.计算结果表明,非次序双电离产率随着椭偏率的增大而减小;双电离得到的电子对在激光偏振平面长轴方向的末态关联动量谱呈现正关联,在激光偏振平面短轴方向的末态关联动量谱呈现反关联;Ar2+在激光偏振平面短轴方向的末态动量谱呈现单峰结构,并且随着椭偏率增大而变宽.轨迹分析显示,椭圆偏振激光脉冲驱动下,非次序双电离仍然是通过再碰撞而发生;随着椭偏率的增大,有效碰撞和单电离之间的时间延迟增加,这是因为椭偏率较大时第一个电子需要经过多次往返才能与母核离子发生有效碰撞. 相似文献
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We show that the recently reported momentum distribution of recoil ions from laser induced nonsequential double ionization can be interpreted as a combined effect of interelectron correlation and final state field interaction ("Volkov dressing") of the two outgoing electrons. We also find a cutoff formula for the recoil momentum that gives the maximum momenta observed in the experiments. 相似文献
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Effect of elliptical polarizations on nonsequential double ionization in two-color elliptically polarized laser fields 下载免费PDF全文
Using the classical ensemble model, we investigate the nonsequential double ionization(NSDI) of Ar and Mg in the two-color elliptically polarized laser pulse for different elliptical polarizations. Numerical results show that for Ar atoms the NSDI yield increases as the ellipticity increases, which is different from the case of Mg atoms. Moreover, the correlated behavior in the correlated electron momentum along the x direction and ion momentum distributions of Ar atoms are influenced by the ellipticity. By statistical analysis of different times, we can conclude that the ellipticity may be responsible for the NSDI processes. The correlated momenta distributions along the x direction at the recollision time are demonstrated and the results show that the travelling time and ellipticity can affect the emitted directions of both electrons. 相似文献
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Electron correlations in nonsequential double ionization of argon atoms by elliptically polarized laser pulses 下载免费PDF全文
Using a classical ensemble model, we investigate the correlation behaviour of electrons originating from nonsequential double ionization (NSDI) of argon atoms by the elliptically polarized laser pulses. Because of the ellipticity, not only the first electron to return but also the later return of tunneled electrons contribute significantly to NSDI. We mainly discuss two kinds of events of NSDI originating from the first and the second return separately. For the NSDI resulting from the recollision of the first return, the correlated electron momentum spectrum along the long axis of the laser polarization plane reveals an obvious V-like shape, located at the first and third quadrant. However, for the NSDI resulting from the recollision of the second return, the momenta of two electrons are distributed in the four quadrants uniformly. By analysing the trajectories of these two kinds, we find that the recollision energy and the laser phase at recollision are different for the first and second returning trajectories, which are responsible for the difference in the correlated behavior of the final electron momentum. 相似文献