LENS European Laboratory for Non-Linear Spectroscopy, and Dipartimento di Fisica e Astronomia, Università di Firenze, Sesto Fiorentino, 50019, Italy.
Istituto Nazionale di Ottica, INO-CNR, Sesto Fiorentino, 50019, Italy.
Sci Rep. 2018 Jan 22;8(1):1301. doi: 10.1038/s41598-018-19814-z.
Laser cooling based on dark states, i.e. states decoupled from light, has proven to be effective to increase the phase-space density of cold trapped atoms. Dark-states cooling requires open atomic transitions, in contrast to the ordinary laser cooling used for example in magneto-optical traps (MOTs), which operate on closed atomic transitions. For alkali atoms, dark-states cooling is therefore commonly operated on the D transition nS → nP. We show that, for Rb, thanks to the large hyperfine structure separations the use of this transition is not strictly necessary and that "quasi-dark state" cooling is efficient also on the D line, 5S → 5P. We report temperatures as low as (4.0 ± 0.3) μK and an increase of almost an order of magnitude in the phase space density with respect to ordinary laser sub-Doppler cooling.
基于暗态的激光冷却，即与光解耦的状态，已被证明可以有效地增加冷捕获原子的相空间密度。与例如用于磁光阱 (MOT) 的普通激光冷却相比，暗态冷却需要开放的原子跃迁，后者则在封闭的原子跃迁上运行。因此，对于碱金属原子，暗态冷却通常在 D 跃迁 nS → nP 上进行。我们表明，对于 Rb，由于大的超精细结构分离，使用此跃迁并非严格必要，并且“准暗态”冷却在 D 线 5S → 5P 上也很有效。我们报告的温度低至 (4.0 ± 0.3) μK，与普通激光亚多普勒冷却相比，相空间密度增加了近一个数量级。
