Based on a multilevel model considering enough bound electronic states of atoms, we theoretically study the role of the transition dipole phase (TDP) in the attosecond transient absorption (ATA) spectrum of helium in intense laser fields. By solving the stationary Schrödinger equation with B-spline basis sets, we first calculate the transition dipole moments with well-defined phases between the bound states. Using the modified multilevel model, we reveal that the TDP plays an important role in determining the spectral structures if two or more paths populate the excited states from the ground state. Our multilevel model with the accurate TDP is convenient to address the origin of atomic ATA spectral structures by freely removing or adding specific electronic states and has been justified by comparing with the ATA spectra via directly solving the time-dependent Schrödinger equation. Hopefully, further incorporating macroscopic propagation into the model will provide indepth physical insights into experimental ATA spectra.

中文翻译：

---

多能级模型中跃迁偶极相在原子阿秒瞬态吸收中的作用。

基于考虑原子的足够束缚电子态的多级模型，我们从理论上研究了跃迁偶极子相（TDP）在强激光场中氦的阿秒瞬态吸收（ATA）光谱中的作用。通过用B样条基集解平稳的Schrödinger方程，我们首先计算出束缚态之间具有明确定义的相位的跃迁偶极矩。使用修改后的多级模型，我们揭示了如果两个或更多路径从基态填充激发态，则TDP在确定光谱结构中起着重要作用。我们的具有精确TDP的多级模型可通过自由地去除或添加特定的电子态来方便地解决原子ATA光谱结构的起源，并且通过直接求解时间相关的Schrödinger方程与ATA光谱进行比较已证明了这一点是正确的。希望进一步将宏观传播纳入模型中，将为实验ATA光谱提供深入的物理见解。