Features of molecular structure beneficial for optical pumping
Features of molecular structure beneficial for optical pumping
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DOI：
10.1103/physreva.107.033110
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发表时间：
2022-08
影响因子：
2.9
通讯作者：
James Dragan;I. Antonov;B. Odom
中科院分区：
文献类型：
--
作者：
James Dragan;I. Antonov;B. Odom
通过光抽运可以实现快速有效的分子态制备。最明显促进循环的分子结构涉及强电子跃迁，具有有利的振动分支（对角弗兰克-康登因子，又名FCF），并且没有任何介入的电子状态。在这里，我们提出了重要的调整，这些标准的基础上，我们的经验光学泵浦SiO$^+$。具体而言，不介入电子状态的偏好应该得到修改，过度依赖FCF可能会错过重要的功能。SiO ^+$中的介入电子态实际上被发现有利于基态旋转态的制备，通过提供一条路径使布居经历宇称翻转。这一贡献表明，通过干预状态的衰变可能有助于非对角或多原子分子的状态准备。我们还扩展了有利分支的定义。在SiO$^+$中，我们发现非对角FCF不能反映振动加热与冷却速率。由于分支率是由跃迁偶极矩（TDM）决定的，我们引入了一个简单的模型来近似非对角衰变的TDM。我们发现，两项，主要由偶极矩函数的斜率（$d\mu/dx$）和平衡键长的偏移（$\Delta x = r_e^g-r_e^e$）设置，可以加（减）以增加（减少）给定TDM的幅度。将该模型应用于SiO$^+$，我们发现有一个偶然的抵消，其中导致振动激发的衰变减少，导致光学循环自然导致振动冷却。
Fast and efficient state preparation of molecules can be accomplished by optical pumping. Molecular structure that most obviously facilitates cycling involves a strong electronic transition, with favorable vibrational branching (diagonal Franck-Condon factors, aka FCFs) and without any intervening electronic states. Here, we propose important adjustments to those criteria, based on our experience optically pumping SiO$^+$. Specifically, the preference for no intervening electronic states should be revised, and over-reliance on FCFs can miss important features. The intervening electronic state in SiO$^+$is actually found to be beneficial in ground rotational state preparation, by providing a pathway for population to undergo a parity flip. This contribution demonstrates the possibility that decay through intervening states may help state preparation of non-diagonal or polyatomic molecules. We also expand upon the definition of favorable branching. In SiO$^+$, we find that the off-diagonal FCFs fail to reflect the vibrational heating versus cooling rates. Since the branching rates are determined by transition dipole moments (TDMs) we introduce a simple model to approximate the TDMs for off-diagonal decays. We find that two terms, set primarily by the slope of the dipole moment function ($d\mu/dx$) and offset in equilibrium bond lengths ($\Delta x = r_e^g-r_e^e$), can add (subtract) to increase (decrease) the magnitude of a given TDM. Applying the model to SiO$^+$, we find there is a fortuitous cancellation, where decay leading to vibrational excitation is reduced, causing optical cycling to lead naturally to vibrational cooling.