近日，美国内布拉斯加大学的J. M. Ngoko Djiokap及其研究团队取得一项新进展。他们实现了由反圆偏振激光脉冲产生的光电子动量分布的拉比振荡变换。相关研究成果已于2024年12月9日在国际知名学术期刊《物理评论A》上发表。

该研究团队报道了相干拉比型动力学和奥特勒-汤斯（Autler-Townes，AT）双峰形成的潜力，它们能够通过从头算含时薛定谔方程计算，显著改变氢原子共振双光子电离过程中，产生的光电子动量分布（PMD）图案。当这一非线性过程由单个持续时间长于拉比周期的圆偏振（CP）激光脉冲驱动时，AT双峰会调制PMD中的圆形对称图案，并产生两个同心带。

当第二个具有相反螺旋度的CP激光脉冲以同步方式作用时，PMD中的双重四极图案会分裂为两部分（慢电子和快电子），每部分都继承了C₂旋转对称性。

当两个脉冲在时间上逐渐分离时，零时延下报道的双重四极分裂图案会旋转，从而产生分离的螺旋图案，但PMD中直接可视化这些图案可能会受到AT最小值显著强度的影响，以及激光频率失谐引起的畸变所阻碍，这一点可从方位角积分能量分布中看出。由于两个量子态的叠加是物质中电荷迁移活动的基础，因此这些在不同脉冲参数范围内持续存在的分离螺旋图案，为揭示复杂系统中的电荷迁移提供了一条途径。

附：英文原文

Title: Transformation by Rabi oscillation of the photoelectron momentum distribution produced by oppositely circularly polarized laser pulses

Author: E. L. Fulton, J. M. Ngoko Djiokap

Issue&Volume: 2024/12/09

Abstract: We report on the potential of coherent Rabi-type dynamics and the formation of the Autler-Townes (AT) doublet to dramatically transform the patterns emerging in the photoelectron momentum distribution (PMD) produced in resonant two-photon ionization of the hydrogen atom by means of ab initio time-dependent Schrdinger equation calculations. When this nonlinear process is driven by a single circularly polarized (CP) laser pulse with a duration longer than the Rabi period, the AT doublet is shown to modulate the circular symmetric pattern in the PMD and yield two concentric bands. When a second CP laser pulse with opposite helicity acts in a synchronous way, the twofold quadrupolar pattern in the PMD sunders to yield two parts (slow and fast electrons), with each inheriting the C₂ rotational symmetry. When the two pulses are gradually separated in time, the twofold quadrupolar asunder patterns reported for zero time delay then rotate to produce parted spirals, whose direct visualization in the PMD may be impeded by the significant intensity of the AT minimum as revealed by the azimuthal angle-integrated energy distribution as well as by distortions from detuning the laser frequency. As the superposition of two quantum states is the basis of charge migration activities in matter, these spirals-asunder, persisting among a range of pulse parameters, provide an avenue for revealing charge migration in complex systems.

DOI: 10.1103/PhysRevA.110.063105

Source: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.110.063105