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Photoassociation and coherent transient dynamics in the interaction of ultracold rubidium atoms with shaped femtosecond pulses. I. Experiment

: Mullins, T.; Salzmann, W.; Götz, S.; Albert, M.; Eng, J.; Wester, R.; Weidemüller, M.; Weise, F.; Merli, A.; Weber, S.M.; Sauer, F.; Wöste, L.; Lindinger, A.


Physical Review. A 80 (2009), Nr.6, Art. 063416
ISSN: 0556-2791
ISSN: 1050-2947
ISSN: 1094-1622
Fraunhofer IPM ()

We experimentally investigate various processes present in the photoassociative interaction of an ultracold atomic sample with shaped femtosecond laser pulses as an detailed extension of previous work. We demonstrate the photoassociation of pairs of rubidium atoms into electronically excited, bound molecular states using spectrally cut femtosecond laser pulses tuned below the rubidium D1 or D2 asymptote. Time-resolved pump-probe spectra reveal oscillations of the molecular formation rate, which are due to coherent transient dynamics in the electronic excitation. The oscillation frequency corresponds to the detuning of the spectral cut position to the asymptotic transition frequency of the rubidium D1 or D2 lines, respectively. Measurements of the molecular photoassociation signal as a function of the pulse energy reveal a nonlinear dependence and indicate a nonperturbative excitation process. Chirping the association laser pulse allowed us to change the phase of the coh erent transients. Furthermore, a signature for molecules in the electronic ground state is found, which is attributed to molecule formation by femtosecond photoassociation followed by spontaneous decay. In a subsequent article quantum mechanical calculations are presented, which compare well with the experimental data and reveal further details about the observed coherent transient dynamics.