Vibrational State Transfer in Ultracold NaCs

Ultracold polar NaCs molecules are formed via photoassociation through a resonance 23 GHz detuned from the Cs 6$^{2}$P$_{3/2}$ asymptote from overlapped dark-spot Magneto-Optical Traps. Using a vibrational state selective detection method, we have determined the sample consists of $\nu $=4-19 in the X$^{1}\Sigma ^{+}$ electronic ground state. We will report on an optical pumping method designed to transfer this initial distribution of vibrational levels to maximize the $\nu $=0 population.~A simple model of optical pumping using the A$^{1}\Sigma ^{+}$ - b$^{3}\Pi $ complex is used to predict that the population will accumulate in the $\nu $=0 state if the sample is illuminated with light at roughly 1 micron with a 10 nm spectral range. Most importantly, the pulse frequency must be shaped to exclude transitions out of the $\nu $=0 level in order to create a dark state where the population will accumulate [1]. \\[4pt] [1] D. Sofikitis, et al. PRA 80 051401 (2009)