标题： O$_2^+$中的旋转相干性在强场电离后 显示英文标题

标题： Rotational coherences in O$_2^+$ following strong-field ionization

摘要： 我们研究了在强场电离后仍束缚在氧的基态和激发态阳离子中的波包。 使用较弱的探测脉冲（800或264纳米）来解离这些仍束缚的阳离子。 测量了O$^+$的动量分布随泵浦-探测延迟的变化，并进行傅里叶变换以获得与动能相关和旋转态分辨的量子振荡光谱。 傅里叶变换的亚厘米$^{-1}$分辨率允许明确识别由泵浦激发并由探测解离的电子、振动和旋转态。 尽管预期强场电离会比$b^4\Sigma^{-}_g$态更有效地激发较低的$X^2\Pi_g$和$a^4\Pi_u$态，但仅在使用264纳米探测脉冲时观察到$X^2\Pi_g$态的波包，且无论使用哪种探测脉冲，仅发现$a^4\Pi_u$态的微弱特征。 实验通过800 nm脉冲[Xue\textit{等.}, Phys. Rev. A 97, 043409 (2018)]确认了$b^4\Sigma^{-}_g$和$a^4\Pi_u$态之间的共振耦合的作用，并揭示了转动振动激发在确定O$^+$碎片动量分布中的重要性。使用264 nm探测脉冲观察到的强$X^2\Pi_g$态贡献也显示了共振耦合在探测脉冲中的重要性。 子厘米$^{-1}$分辨率也解决了$X^2\Pi_g$和$a^4\Pi_u$状态波包中的自旋-轨道分裂。 显示英文摘要

摘要： We investigate the wave packet that remains bound in the ground and excited cationic states of oxygen after strong-field ionization by an intense 800-nm pulse. Much weaker probe pulses (800 or 264 nm) are used to dissociate these still-bound cations. The momentum distribution of O$^+$ is measured as a function of pump-probe delay and Fourier-transformed to obtain kinetic-energy-dependent and rotational-state-resolved quantum beat spectra. The sub-cm$^{-1}$ resolution of the Fourier transform allows unambiguous identification of the electronic, vibrational, and rotational states populated by the pump and then dissociated by the probe. Although strong-field ionization is expected to populate the lower-lying $X^2\Pi_g$ and $a^4\Pi_u$ states more effectively than the $b^4\Sigma^{-}_g$ state, a wave packet in the $X^2\Pi_g$ state is seen only with the 264-nm probe and only weak signatures of the $a^4\Pi_u$ states are found with either probe. The experiment confirms the role of the resonant coupling between the $b^4\Sigma^{-}_g$ and $a^4\Pi_u$ states by the 800 nm pulses [Xue \textit{et al.}, Phys. Rev. A 97, 043409 (2018)] and reveals the importance of rovibrational excitation in determining the momentum distribution of the O$^+$ fragments. The strong $X^2\Pi_g$ state contribution observed with the 264-nm probe also shows the importance of resonant coupling in the probe pulse. The sub-cm$^{-1}$ resolution also resolves spin-orbit splitting in both the $X^2\Pi_g$ and $a^4\Pi_u$ state wave packets.