Coherent control of cold-molecule formation through photoassociation usinga chirped-pulsed-laser field - art. no. 013412

Enhancement of the production of cold molecules via photoassociation is con sidered for the Cs-2 system. The employment of chirped picosecond pulses is proposed and studied theoretically. The analysis is based on the ability t o achieve impulsive excitation which is given by the ultracold initial cond itions where the nuclei are effectively stationary during the interaction w ith a field. The appropriate theoretical framework is the coordinate-depend ent two-level system. Matching the pulse parameters to the potentials and i nitial conditions results in full Rabi cycling between the electronic poten tials. By chirping the laser pulse, adiabatic transfer leading to the popul ation inversion from the ground to the excited state is possible in a broad and tunable range of internuclear distance. Numerical simulations based on solving the time-dependent Schrodinger equation (TDSE) were performed. The simulation of the photoassociation of Cs-2 from the ground (3)Sigma (+)(u) to the excited 0(g)(-) state under ultracold conditions verifies the quali tative picture. The ability to control the population transfer is employed to optimize molecular formation. Transfer of population to the excited 0(g) (-) surface leaves a void in the nuclear density of the ground (3)Sigma (+) (u) surface. This void is either filled by thermal motion or by quantum "pr essure" and it is the rate-determining step in the photoassociation. The sp ontaneous-emission process lending to cold-molecules is simulated by includ ing an optical potential in the TDSE. Consequently, the rate of cold molecu le formation in a pulsed mode is found to be larger than that obtained in a continuous-wave mode.