We investigate different approximations in a polarization control scheme in two-color two-photon ionization by means of second-order time-dependent perturbation theory. Experiments revealed light-polarization dependencies in the above-threshold ionization of water molecules assisted by an IR field. These experiments were performed at photoelectron energies at which the soft-photon approximation exhibits discrepancies. We show that these discrepancies may be attributed to the coulombic nature of the scattering process for continuum–continuum transitions.

中文翻译：

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双色水分子电离极化控制的不同近似

我们通过二阶时间相关微扰理论研究了双色双光子电离中偏振控制方案的不同近似值。实验揭示了在红外场辅助下的水分子阈值以上电离中的光偏振依赖性。这些实验是在软光子近似表现出差异的光电子能量下进行的。我们表明，这些差异可能归因于连续-连续跃迁散射过程的库仑性质。