Strong-field atomic experiments have recently become sensitive to nondipole (magnetic) interactions. In particular, photoelectrons emitted in above-threshold ionization possess a nonzero momentum along the beam axis as a result of the Lorentz force. Here, we show how this longitudinal momentum can be theoretically calculated based on a nondipole strong-field approximation that accounts not only for the temporal but also the spatial dependence of the laser field in the photoelectron continuum. If the driving laser beam is approximated as a plane wave, the theoretical values differ from known experimental results by a constant offset. We demonstrate that this offset can successfully be removed if a realistic Gaussian beam profile is accounted for in the quantum description of ATI. We also discuss the influence of the size of the beam waist in the focus.

强场原子实验最近对非偶极（磁）相互作用变得敏感。特别是，由于洛伦兹力，在高于阈值电离中发射的光电子沿束轴具有非零动量。在这里，我们展示了如何基于非偶极强场近似从理论上计算这种纵向动量，该近似不仅解释了光电子连续谱中激光场的时间依赖性，而且还考虑了空间依赖性。如果将驱动激光束近似为平面波，则理论值与已知实验结果存在恒定偏移。我们证明，如果在 ATI 的量子描述中考虑了现实的高斯光束轮廓，则可以成功消除这种偏移。