Fine-structure changing collisions in 87Rb upon D2 excitation in the hyperfine Paschen-Back regime [dataset]

We investigate fine structure changing collisions in 87Rb vapour upon D2 excitation in a thermal vapour at 350 K; the atoms are placed in a 0.6 T axial magnetic field in order to gain access to the hyperfine Pashen-Back regime. Following optical excitation on the D2 line, the exothermic transfer 5P3/2 →5P1/2 occurs as a consequence of buffer-gas collisions; the 87Rb subsequently emits a photon on the D1 transition. We employ single-photon counting apparatus to monitor the D1 fluorescence, with an etalon filter to provide high spectral resolution. By studying the D1 fluorescence when the D2 excitation laser is scanned, we see that during the collisional transfer process the mJ quantum number of the atom changes, but the nuclear spin projection quantum number, mI , is conserved. A simple kinematic model incorporating a coefficient of restitution in the collision accounted for the change in velocity distribution of atoms undergoing collisions, and the resulting fluorescence lineshape. The experiment is conducted with a nominally “buffer-gas free” vapour cell; our results show that fine structure changing collisions are important with such media, and point out possible implications for quantum-optics experiments in thermal vapours producing entangled photon pairs with the double ladder configuration, and solar physics magneto-optical filters.

本研究针对350K热蒸气环境下，经D₂线激发的铷-87（⁸⁷Rb）蒸气中的精细结构改变碰撞展开探究。实验中将原子置于0.6T的轴向磁场中，以进入超精细帕邢-巴克（Paschen-Back）区域。在D₂线完成光激发后，由于缓冲气体碰撞，原子会发生放热跃迁5P₃/₂ → 5P₁/₂；随后铷-87原子将在D₁跃迁过程中辐射出一个光子。本研究采用单光子计数装置监测D₁荧光，并搭配标准具滤波器以实现高光谱分辨率。通过扫描D₂激发激光并观测D₁荧光，我们发现：在碰撞转移过程中，原子的磁量子数m_J会发生改变，但核自旋投影量子数m_I保持守恒。本研究构建了一个包含碰撞恢复系数的简化运动学模型，该模型可解释碰撞原子的速度分布变化以及由此产生的荧光线形。本实验采用名义上"buffer-gas free"的蒸气气室开展；研究结果表明，此类介质中的精细结构改变碰撞效应不可忽略，同时本研究还指出该现象对热蒸气环境下的两类量子光学实验具有潜在参考价值：一类是通过双梯级构型制备纠缠光子对的实验，另一类是太阳物理领域的磁光滤波器相关实验。