Excited-state spectroscopy for producing ultracold ground-state NaRb molecule

We report a joint experimental and theoretical investigation on the excited states of NaRb molecule. In particular, we focus on the A$^1\Sigma^+$/b$^3\Pi$ admixture which is a promising intermediate state for transferring weakly-bound NaRb Feshbach molecules to the $v$ = 0 level of the X$^1\Sigma^+$ state. Based on RKR potentials obtained from conventional molecular spectroscopy [1], we identified several levels which satisfy the requirements for efficient two-photon population transfer. Starting from a pure sample of NaRb Feshbach molecules, we have experimentally observed most of these levels. The detailed characterization of these levels, including their transition strengths and singlet/triplet mixing ratios, as well as searching of the $v$ = 0 level of the X$^1\Sigma^+$ state with two-photon Autler-Townes spectroscopy, are well underway.