  We describe experiments and associated quantum simulations involving the
production of ultracold $^{87}$Rb$_{2}$ molecules with nanosecond pulses of
frequency-chirped light. With appropriate chirp parameters, the formation is
dominated by coherent processes. For a positive chirp, excited molecules are
produced by photoassociation early in the chirp, then transferred into high
vibrational levels of the lowest triplet state by stimulated emission later in
the chirp. Generally good agreement is seen between the data and the
simulations. Shaping of the chirp can lead to a significant enhancement of the
formation rate. Further improvements using higher intensities and different
intermediate states are predicted.
