We investigate the discrete orbital angular momentum (OAM) of photoelectrons freed in strong-field ionization. We use these ‘twisted’ electrons to provide an alternative interpretation on existing experimental work of vortex interferences caused by strong field ionization mediated by two counter-rotating circularly polarized pulses separated by a delay. Using the strong field approximation, we derive an interference condition for the vortices. In computations for a neon target we find very good agreement of the vortex condition with photoelectron momentum distributions computed with the strong field approximation, as well as with the time-dependent methods Qprop and R-Matrix. For each of these approaches we examine the OAM of the photoelectrons, finding a small number of vortex states localized in separate energy regions. We demonstrate that the vortices arise from the interference of pairs of twisted electron states. The OAM of each twisted electron state can be directly related to the number of arms of the spiral in that region. We gain further understanding by recreating the vortices with pairs of twisted electrons and use this to determine a semiclassical relation for the OAM. A discussion is included on measuring the OAM in strong field ionization directly or by employing specific laser pulse schemes as well as utilizing the OAM in time-resolved imaging of photo-induced dynamics.

中文翻译：

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在强场电离中操纵扭曲的电子

我们研究了在强场电离中释放的光电子的离散轨道角动量（OAM）。我们使用这些“扭曲”电子为现有实验工作提供另一种解释，该实验工作是由两个由延迟分开的反向旋转的圆极化脉冲介导的强场电离引起的涡旋干扰。使用强场近似，我们得出了涡旋的干扰条件。在霓虹灯目标的计算中，我们发现涡旋条件与通过强场近似以及时间相关方法Qprop和R-Matrix计算的光电子动量分布非常吻合。对于这些方法中的每一种，我们都会检查光电子的OAM，找到位于单独能量区域中的少量涡旋状态。我们证明了涡流是由成对的扭曲电子态的干扰引起的。每个扭曲电子态的OAM可以直接与该区域中螺旋臂的数量有关。通过用成对的扭曲电子对重现涡旋并以此来确定OAM的半经典关系，我们获得了进一步的理解。讨论包括直接在强场电离中或通过使用特定的激光脉冲方案测量OAM，以及在光感应动力学的时间分辨成像中使用OAM。通过用成对的扭曲电子对重现涡旋并以此来确定OAM的半经典关系，我们获得了进一步的理解。讨论包括直接在强场电离中或通过使用特定的激光脉冲方案测量OAM，以及在光感应动力学的时间分辨成像中使用OAM。通过用成对的扭曲电子对重现涡旋并以此来确定OAM的半经典关系，我们获得了进一步的理解。讨论包括直接在强场电离中或通过使用特定的激光脉冲方案测量OAM，以及在光感应动力学的时间分辨成像中使用OAM。