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Ultracold Atom Collisions Probed With Ultrashort Laser Pulses



F K. Fatemi, Kevin Jones, Paul D. Lett


Photoassociation, the light-assisted formation of molecules, has become a powerful tool for studying weakly bound molecules, and for extracting atomic properties with high resolution. However, few experiments have focused on the dynamics of these collisions. We have used short laser pulses to examine the process by which two ground state sodium atoms cooled to 0.5 mK in a magnetooptic trap absorb two photons tuned to the atomic 3S -> 3P transition (16973 cm-1) to produce a molecular ion:Na(3S) + Na(3S) + 2hv -> Na2+ + e-The 10 ps duration pulses are split into two equal pulses with the second pulse delayed up to 12 ns relative to the first. The rate of molecule formation is dependent upon the time delay between the pump and probe pulses, T, and we can identify three time scales. For T {approximately equal to} 10 ps, we see a slight autocorrelation of the pump and probe pulses. For T 4 ns) the enhancement diminishes due to the molecular radiative lifetime ({approximately equal to} 10 ns).We suggest a picture whereby the first laser pulse excites the colliding atom pair to the asymptote of the 3S + 3P potential, which varies with internuclear distance R as 1/R3 at long range. The second laser pulse promotes this system to the 3P + 3Ppotential, which is a much shorter range potential, varying as 1/R5. Long pump-probe delay times allow the atom pair to accelerate on the intermediate potential, so that they have enough speed on the 3P+3P potential to undergo associativeionization before radiatively decaying, producing an enhancement in the molecular ion signal. This behavior has been modeled with numerical simulations that present a conceptually simple yet accurate picture of the collision dynamics.
Proceedings Title
Sigma Xi Post Doctoral Poster Presentations, 2000
Conference Dates
February 17-18, 2000
Conference Title
Sigma Xi Web Page


atom collisions, photoassociation, ultracold atom collisions, weakly bound molecules


Fatemi, F. , Jones, K. and Lett, P. (2000), Ultracold Atom Collisions Probed With Ultrashort Laser Pulses, Sigma Xi Post Doctoral Poster Presentations, 2000 (Accessed June 15, 2024)


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Created February 1, 2000, Updated February 17, 2017