Steering photoassociation of cold 85Rb atoms by two-color slowly-turned-on and rapidly-turned-off laser pulses

Photoassociation (PA) of 85Rb atoms from the ground X1Σg+ state to the excited A1Σg+ and b3Πu states by two-color laser pulses at 100 μK×kB is investigated by using quantum wavepacket method. Two pulses with detunings δ 1 and δ 2 varying from −1.0 to 1. cm−1 are taken into account. The specific case δ1=−δ2 is generalized to the condition of arbitrary combination of δ 1 and δ 2 for both the Gaussian-pulse field and the slowly-turned-on and rapidly-turned-off (STRT) field. It is found that the introduce of the detunings in the two pluses can enhance the asymmetry of the time profile and broaden the linewidth of the laser field. The two factors can further enhance the PA probability for both resonant and nonresonant regions. Compared to the Gaussian field, the STRT field which is even more asymmetric in time profile and more broaden in linewidth can significantly enhance the PA probability, with the nonresonant transition dominating the PA process. It can be expected that once the two detunings are both positive, which is a relatively loose restriction for coherent control, a considerable PA probability can be obtained in a two-color STRT field.