Effect of Nanosecond-Timescale Frequency-Chirped Light on Ultracold $^{85}$Rb$_2$ Ground-State Formation

We report on progress towards ultracold $^{85}$Rb$_2$ formation using frequency-chirped light on the nanosecond-timescale in a Magneto-Optical Trap (MOT). In previous work, we showed coherent control of ultracold atomic $^{85}$Rb trap-loss collisions with chirped light. In our current research, we use Resonantly-Enhanced Multi-Photon Ionization (REMPI) to directly detect ground-state $^{85}$Rb$_2$ molecules. Either positive or negative chirps, centered at a variable detuning below the \emph{D$_2$} line, sweep over 1 GHz in 100 ns. The effect of these chirps on the formation of ground-state $^{85}$Rb$_2$ in the MOT is compared to that of a CW probe laser. While initial experiments have shown an increase in atomic trap-loss with the addition of either the frequency-chirped light or the CW probe, a reduction in MOT-formed ground-state $^{85}$Rb$_2$ is seen. This work is supported by DOE.