Two-photon cooling below the Doppler limit in bosonic magnesium

Standard sub-Doppler cooling methods are not applicable in bosonic magnesium due to the non-degenerate ground state. However, the Doppler limit can be surpassed by coupling the excited state of the cooling transition to the level ¹D₂ and cooling via a coherent two-photon transition. This process modifies the population in ¹P₁, similar to electromagnetically induced transparency, as well as the resulting force profile in optical molasses. These modifications can be used to obtain a steeper slope in the force profile around v=0 and hence lower temperatures as compared to doppler cooling on the strong transition only.