Controlling vibrational wave packet revivals in condensed phase:: Dispersion and coherence for Br2 in solid Ar

Interferences in vibrational wave packets of Br-2 molecules are controlled in the presence of a solid Ar environment that provides decoherence. By applying a negatively or positively chirped excitation pulse, one can set the clock backward, respectively forward, in the wave packet propagation. Based on this mechanism, we present a general scheme to record vibrational decoherence. Wave packets are spatially focused at T-opt by applying negatively chirped pulses. From the focussing contrast, we determine a vibrational dephasing time on the B state of T-deph(vib) = 3 ps. We use positively chirped pulses to bring the formation of fractional revival structures forward with respect to T-deph(vib). By exciting four vibrational levels with such a pulse, we observe a 1/6 revival indicating the vibrational coherence time T-deph(4) for exactly four levels. The required chirp prolongs the pulse duration by a factor of ten to Deltatau = 300 fs. Electronic dephasing T-deph(el) restricts the revival control efficiency to parts of the pulse with Deltatau < T-deph(el), which allows to derive T-deph(el) > 300 fs.