Investigation of a resonantly coupled photoassociation resonance for production of ultracold, polar molecules in the absolute vibrational ground state

We report on the discovery of a photoassociation (PA) resonance in NaCs which efficiently populates $X^{1}\Sigma^{+} (v=0)$, and on our progress in detecting these molecules. We found the resonance while performing PA spectroscopy detuned from the Cs $6^{2}$P$_{1/2}$ asymptote, and we discuss our analysis of this spectrum. The effeciency of the observed PA resonance in producing deeply bound $X^{1}\Sigma^{+}$ molecules is due to resonant coupling with $v = 17$ in the $B^{1}\Pi$ electronic state. The rotational quanta 0-4 are coupled, though the strongest coupling appears in J = 1 and 2. In order to detect the absolute vibrational ground state, we plan to perform two-color Resonance Enhanced Multi-Photon Ionization using the fundamental and 2nd harmonic output of a KDP crystal pumped with an infrared pulsed dye laser. We also discuss the prospects for trapping and accumulating molecules in the vibrational ground state.