标题： 钾的D$_2$线在无多普勒效应光谱中的超精细帕申-巴克区 显示英文标题

标题： Hyperfine Paschen-Back regime of Potassium D$_2$ line observed by Doppler-free spectroscopy

摘要： 选择性反射激光辐射从由介电窗口和一个纳米细胞中限制的钾原子蒸气形成的界面，具有$350~$纳米间隙厚度，首次被实现以研究外部磁场中的 K D$_2$线的原子跃迁。在中等$B$场中，有44个单独的Zeeman跃迁，随着磁场的增加，这些跃迁减少为两组（一组由$\sigma^+$组成，另一组由$\sigma^-$组成），每组包含八个原子跃迁，分别由圆偏振光形成。每组包含一个所谓的“引导”跃迁，其特点是概率（强度）以及频率漂移斜率（以MHz/G为单位）在整个$0 - 10~$kG磁场范围内保持恒定。 在$\pi$极化激光辐射的情况下，八条跃迁中有两条在$B = 0$处被禁止，但在磁场的影响下它们的概率会发生巨大的变化。 我们证明对于$B$场$> 165~$G，观察到了完整的超精细帕申-巴克效应。 还介绍了K D$_2$线在磁场中的其他特殊行为。 我们展示了理论计算与实验之间非常好的一致性。 首次展示了以高光谱分辨率记录K D$_2$线的超精细帕申-巴克效应。 显示英文摘要

摘要： Selective reflection of a laser radiation from an interface formed by a dielectric window and a potassium atomic vapour confined in a nano-cell with $350~$nm gap thickness is implemented for the first time to study the atomic transitions of K D$_2$ line in external magnetic fields. In moderate $B$-fields, there are 44 individual Zeeman transitions which reduce to two groups (one formed by $\sigma^+$ the other one by $\sigma^-$ circularly-polarised light), each containing eight atomic transitions, as the magnetic field increases. Each of these groups contains one so-called "guiding" transition whose particularities are to have a probability (intensity) as well as a frequency shift slope (in MHz/G) that are constant in the whole range of $0 - 10~$kG magnetic fields. In the case of $\pi$-polarised laser radiation, among eight transitions two are forbidden at $B = 0$, yet their probabilities undergo a giant modification under the influence of a magnetic field. We demonstrate that for $B$-fields $> 165~$G a complete hyperfine Paschen-Back regime is observed. Other peculiarities of K D$_2$ line behaviour in magnetic field are also presented. We show a very good agreement between theoretical calculations and experiments. The recording of the hyperfine Paschen-Back regime of K D$_2$ line with high spectral resolution is demonstrated for the first time.