We theoretically study photoelectron angular distributions and related anisotropy parameters for the competition of one- and two-photon ionization of He in an ultrashort extreme-ultraviolet laser pulse, using numerical results from the time-dependent Schrödinger equation. We explore the transition between the two processes for variation of the pulse duration, peak intensity, and central frequency or photoelectron energy. In the results obtained for fixed pulse parameters the transition and interference between the processes can be observed in the even ( β 2 , β 4 ) and odd ( β 1 , β 3 ) parameters, respectively, while the onset of the impact of three-photon ionization is observed via β 5 at high peak intensities. Finally, we show that the transition can be observed via the even anisotropy parameters in pulses without carrier-to-envelope stabilization as well as in free-electron laser pulses with ...

中文翻译：

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超短波极紫外激光电离氦

我们使用与时间有关的薛定er方程的数值结果，从理论上研究了在超短极紫外激光脉冲中He的单光子和双光子电离竞争的光电子角分布和相关的各向异性参数。我们探索了两个过程之间的过渡，以改变脉冲持续时间，峰值强度以及中心频率或光电子能。在针对固定脉冲参数获得的结果中，可以分别在偶数（β2，β4）和奇数（β1，β3）参数中观察到过程之间的过渡和干扰，而在3在高峰强度下通过β5观察到光子电离。最后，