We have investigated the double ionization of helium induced by 45 fs, 394 nm linearly polarized laser pulses for intensities (2.5–150) 10¹⁴ W cm⁻². The time evolution of the process was determined by applying the classical ensemble approximation (CEA) model. The results of the calculations obtained for the double-to-single ionization ratio, the momentum distribution of the He²⁺ recoil ion and the correlated two-electron momentum distribution are compared with the recent experimental data of Henrichs et al (2018 Phys. Rev. A 98 043405). The standard CEA model failed to reproduce the basic features of the experiment. A considerable improvement in the description of the experimental data was achieved by including a two-step process in the model: the formation of a transient double excited state in the first step, and the simultaneous release of the two electrons via ‘over the barrier ionization’ in the second step.

我们已经研究了由 45 fs、394 nm 线偏振激光脉冲在强度 (2.5–150) 10 ¹⁴ W cm ^{-2 下}引起的氦双重电离。该过程的时间演变是通过应用经典集合近似 (CEA) 模型来确定的。将双电离比、He ²⁺反冲离子的动量分布和相关的双电子动量分布的计算结果与 Henrichs等人（2018 Phys. Rev）最近的实验数据进行比较.一个98043405）。标准的 CEA 模型未能重现实验的基本特征。通过在模型中包含两步过程，在实验数据的描述方面取得了相当大的改进：第一步中形成瞬态双激发态，并通过“越过势垒电离”同时释放两个电子'在第二步。