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首页> 外文会议>NATO Advanced Research Workshop on Super-Intense Laser-Atom Physics Sep 24-30, 2000 Han-sur-Lesse, Belgium >ENERGY DISTRIBUTION OF TWO-ELECTRON IONIZATION OP HELIUM IN AN INTENSE LASER FIELD
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ENERGY DISTRIBUTION OF TWO-ELECTRON IONIZATION OP HELIUM IN AN INTENSE LASER FIELD

机译：激光场中两电子电离氦的能量分布

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摘要

It is well known that a neutral atom interacting with a strong laser field will ionize at sufficiently high intensity even for photon energies well below the ionization threshold. When the required number of photons becomes very large, this process is best described by the suppression of the Coulomb barrier by the laser's oscillating electric field, allowing the electron to tunnel into the continuum. As the laser intensity is increased, more tightly bound electrons may be successively liberated by this mechanism. Such a sequential multiple ionization, long accepted as a reasonable approach to the formidable problem of a multielectron atom interacting nonperturba-tively with an intense electromagnetic field, provides fair estimates of the various charge state appearance intensities while the tur neling rates are in excellent agreement with single ionization yields. However, more accurate measurements revealed systematic and very large deviations from the tunneling rates: near appearance intensity under standard experimental conditions, the observed double ion yield is several orders of magnitude larger than predicted by the sequential rate. It soon became clear that electrons could not be considered as independent and that electron-electron correlation had to be taken into account. Dynamic correlations have been considered in several theories. First qualitatively in the shakeoff model; then empirically through the e-2e cross-section in the quantum/classical three-step model (tunnel ionization, acceleration by the oscillating electric field and e-2e recollision with the ion); recently through the so-called intense field many-body-S-matrix theory and a purely empirical model of collective tunnel ionization. The validity of these ideas has been examined using numerical models, The measurement of total ion yields over a dynamic range exceeding ten orders of magnitude, a major breakthrough made possible by the availability of high-repetition rate lasers at the beginning of the 90's, was for a long time the only quantitative data to confront theory.
机译：众所周知，即使光子能量远低于电离阈值，与强激光场相互作用的中性原子也会以足够高的强度电离。当所需的光子数量变得非常大时，可以用激光的振荡电场对库仑势垒的抑制来最好地描述该过程，从而使电子能够隧穿进入连续体。随着激光强度的增加，可以通过该机制连续释放更紧密结合的电子。这种连续的多次电离，长期以来被认为是解决多电子原子与强电磁场非扰动相互作用这一可怕问题的合理方法，它提供了对各种电荷态出现强度的合理估计，而成晶速率与单次电离产量。但是，更准确的测量结果显示出与隧穿速率的系统性和非常大的偏差：在标准实验条件下接近表观强度时，观察到的双离子产率比顺序速率所预测的大几个数量级。很快变得很清楚，电子不能被认为是独立的，必须考虑电子与电子的相关性。在几种理论中已经考虑了动态相关。首先是定性模型。然后凭经验通过量子/经典三步模型中的e-2e截面（隧道电离，振荡电场加速和e-2e与离子的碰撞）；最近，通过所谓的强场多体S矩阵理论和集体隧道电离的纯粹经验模型。这些想法的有效性已通过数值模型进行了检验。在超过十个数量级的动态范围内对总离子产率的测量是在90年代初使用高重复频率激光器而取得的重大突破，长期以来，唯一的定量数据要面对理论。

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