Candidates for direct laser cooling of diatomic molecules with the simplest Σ1−Σ1 electronic system

Abstract

We propose to utilize the $^{1}\mathrm{\ensuremath{\Sigma}}{\ensuremath{-}}^{1}\mathrm{\ensuremath{\Sigma}}$ electronic transition system for direct laser cooling of heteronuclear diatomic molecules. AgH, as well as its deuterium isotopolog AgD, is used as an example to illustrate the cooling schemes. Potential-energy curves and relevant molecular parameters of both AgH and AgD, including the spin-orbit constants and the electronic transition dipole moments, are determined in internally contracted multiconfiguration-reference configuration interaction calculations. The highly diagonal Franck-Condon matrices of the $A{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}\ensuremath{-}X{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}$ transitions predicted by the calculations suggest the existence of quasi-closed-cycle transitions, which renders these molecules suitable for direct laser cooling. By solving rate equations numerically, we demonstrated that both AgH and AgD molecules can be cooled from 25 K to 2 mK temperature in approximately 20 ms. Our investigation elucidates and supports the hypothesis that molecules in the simplest $^{1}\mathrm{\ensuremath{\Sigma}}{\ensuremath{-}}^{1}\mathrm{\ensuremath{\Sigma}}$ system can serve as favorable candidates for direct laser cooling.