We present an improved scheme for absorption imaging of alkali atoms at moderate magnetic fields, where the excited state is well in the Paschen–Back regime, but the ground state hyperfine manifold is not. It utilizes four atomic levels to obtain an approximately closed optical cycle. With the resulting absorption of the corresponding two laser frequencies, we extract the atomic column density of a ³⁹K Bose–Einstein condensate. The scheme can be readily applied to all other alkali-like species.

中文翻译：

---

在中等磁场下对碱原子进行高信噪比成像

我们提出了一种改进的方案，用于在中等磁场下对碱原子进行吸收成像，该状态下的激发态在Paschen-Back体制中很好，而基态超精细歧管则没有。它利用四个原子级来获得近似封闭的光学循环。利用相应的两个激光频率的吸收，我们提取了³⁹ K Bose-Einstein冷凝物的原子柱密度。该方案可以容易地应用于所有其他类似碱的物质。