Controlling vibrational wave packet revivals in condensed phase: Dispersion and coherence for Br2 in solid Ar
Interferences in vibrational wave packets of Br2 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 Topt by applying negatively chirped pulses. From the focussing contrast, we determine a vibrational dephasing time on the B state of Tvibdeph = 3 ps. We use positively chirped pulses to bring the formation of fractional revival structures forward with respect to Tvibdeph. By exciting four vibrational levels with such a pulse, we observe a 1/6 revival indicating the vibrational coherence time T4deph for exactly four levels. The required chirp prolongs the pulse duration by a factor of ten to Δτ = 300 fs. Electronic dephasing Teldeph restricts the revival control efficiency to parts of the pulse with Δτ < Teldeph, which allows to derive Teldeph > 300 fs.