强场电离中扭曲电子的操纵
Manipulating Twisted Electrons in Strong-Field Ionization
摘要：
本文研究了强场电离过程中光电子的离散轨道角动量。我们使用这些“扭曲”的电子提供一个替代的解释现有的实验工作的涡旋干扰所造成的强场电离介导的两个反向旋转的圆极化脉冲分离的延迟。利用强场近似，我们导出了涡旋的干涉条件。在计算氖目标，我们发现很好的协议的涡旋条件与计算的光电子动量分布与强场近似，以及与时间相关的方法Qprop和R-矩阵。对于这些方法中的每一个，我们研究的OAM的光电子，发现少量的涡旋状态定位在不同的能量区域。我们证明了涡旋是由扭曲电子态对的干涉引起的。每个扭曲电子态的OAM可以直接与该区域中螺旋臂的数量相关。我们获得进一步的理解，通过重新创建的涡旋与扭曲的电子对，并使用此来确定一个半经典的OAM关系。讨论了在强场电离中直接测量OAM或采用特定的激光脉冲方案以及利用OAM进行光致动力学的时间分辨成像。
英文摘要：
We investigate the discrete orbital angular momentum (OAM) of photoelectrons freed in strongfield 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 counterrotating 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.
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