Jiang Wei-Chao, Shan Jun-Yi, Gong Qihuang, Peng Liang-You
State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871, China.
Collaborative Innovation Center of Quantum Matter, Beijing 100871, China.
Phys Rev Lett. 2015 Oct 9;115(15):153002. doi: 10.1103/PhysRevLett.115.153002. Epub 2015 Oct 8.
By using a model based on the second-order time-dependent perturbation theory, we show that the nonsequential two-photon double ionization of He can be understood in a virtual sequential picture: to excite the final double continuum state |k_{1},k_{2}⟩ by absorbing two photons from the ground state |1s^{2},^{1}S_{0}⟩, the single continuum states |1s,k_{1}⟩ and |1s,k_{2}⟩ serve as the dominant intermediate states. This virtual sequential picture is verified by the perfect agreement of the total ionization cross section, respectively, calculated by this model and by the sophisticated numerical solution to the full-dimensional time-dependent Schrödinger equation. This model, without the consideration of the electron correlation in the final double continuum state, works well for a wide range of laser parameters extending from the nonsequential to the sequential regime. The present Letter demonstrates that the electron correlation in the final double continuum state is not important in evaluating the total cross section, while it is indispensable for an accurate computation of a triply differential cross section. In addition, the virtual sequential picture bridges the sequential and nonsequential two-photon double ionization and reveals connections and distinctions between them.
通过使用基于二阶含时微扰理论的模型，我们表明氦原子的非顺序双光子双电离可以在一个虚拟顺序的图像中得到理解：为了从基态|1s²,¹S₀⟩吸收两个光子来激发最终的双连续态|k₁,k₂⟩，单连续态|1s,k₁⟩和|1s,k₂⟩作为主要的中间态。这个虚拟顺序图像通过该模型计算的总电离截面与全维含时薛定谔方程的精确数值解分别计算得到的结果完全一致得到了验证。该模型在不考虑最终双连续态中的电子关联的情况下，对于从非顺序到顺序区域的广泛激光参数都能很好地工作。本信函表明，最终双连续态中的电子关联在评估总截面时并不重要，而对于精确计算三重微分截面则是不可或缺的。此外，虚拟顺序图像架起了顺序和非顺序双光子双电离之间的桥梁，并揭示了它们之间的联系和区别。
