Sub-Doppler cooling of magnesium fluoride molecules

We present a theoretical approach to achieve sub-Doppler cooling of magnesium fluoride (MgF) molecules by tuning the AC Stark shift with a blue-detuned laser. We study three blue-detuned magneto-optical trapping (MOT) schemes by using the Bayesian optimization method with the optical Bloch equations. We perform a comprehensive analysis of the relationship between the force in the MOT and the velocities and positions of the MgF molecules. Monte-Carlo simulations show that our MOT schemes can achieve a temperature as low as 28 μK and a density as high as 4.0 × 10⁸ cm⁻³ at the conditions of a ratio of two laser intensities of 2:7, a detuning of 3Γ and a polarization configuration of σ⁻-σ⁺. These results provide a clear way for transferring a large number of MgF molecules into a conservative trap to enhance the subsequent cooling such as evaporative or sympathetic cooling.