An important theoretical result is that in the regime where PG cooling functions, the temperature only depends on the ratio of Ω Ω 2 to | γ γ | and that the cooling approaches the recoil limit. These predictions were confirmed experimentally in 1990 when W.D. Phillips et al. observed such scaling in their cesium atoms as well as a temperature of 2.5 μ μ K, 12 times the recoil temperature of 0.198 μ μ K for the D2 line of cesium used in the experiment.