We demonstrate how strong-field multiphoton transitions between dynamically shifted atomic levels can be traced in the energy spectra of emitted photoelectrons. Applying an ultrafast and intense laser pulse, two-photon Rabi oscillations are induced between two bound states of an atom. A third photon from the same pulse directly ionizes the atom, thus the emitted photoelectrons coherently probe the underlying dynamics. As the instantaneous energy of photoelectrons follows the pulse intensity envelope, modulated by the ac Stark shifts, electrons emitted with the same energy but at different times—at the rising and falling edge of the pulse—will interfere leading to pronounced dynamic interference pattern in the spectra. We investigate this phenomenon both numerically and analytically by developing a minimal three-state model that incorporates two-photon coupling and dynamically shifted atomic levels. On the example of atomic lithium (2s → → 4s → continuum) we show how the individual ac Stark shifts and the two-photon Rabi frequency are reflected through the asymmetry, shifting and splitting of the interference structure of the computed photopeaks.

我们演示了如何在发射的光电子能谱中追踪动态移位的原子能级之间的强场多光子跃迁。施加超快且强烈的激光脉冲，在一个原子的两个束缚态之间引发了两个光子的拉比振荡。来自同一脉冲的第三个光子直接使原子电离，因此发射的光电子相干地探测了潜在的动力学。当光电子的瞬时能量遵循由ac Stark位移调制的脉冲强度包络线时，以相同能量但在不同时间（在脉冲的上升沿和下降沿）发射的电子将发生干涉，从而导致显着的动态干涉图样。光谱。我们通过开发结合了两个光子耦合和动态移动原子能级的最小三态模型，从数字和分析角度研究了这一现象。以原子锂为例（2s →→4 s →连续），我们展示了如何通过计算光峰的干涉结构的不对称，平移和分裂来反映单个ac斯塔克频移和双光子拉比频率。