Stochastic Schrodinger equation. II. A study of the coherence seen in pump-probe experiments that use a strong pump laser

We use the stochastic Schrodinger equation approach to examine an experimen t performed by Scherer, Jonas, and Fleming [J. Chem. Phys. 99, 153 (1993)]. They have excited I-2 molecules dissolved in n-hexane with a strong, ultra short pump pulse. This creates moving wave packets on both the excited and the ground electronic states. The coherent motion of these packets is studi ed by measuring the absorption of a weak probe pulse, as a function of the delay time between the pulses. We show how the oscillations in the signal a re connected to different excitation mechanisms and to the interference bet ween various packets created by the lasers. Our purpose is to clarify the d ynamics of the packets and to show that the stochastic Schrodinger equation approach can be used to study their decoherence. We did not intend to try to develop a realistic model for the I-2 dynamics and its interaction with the solvent and do not perform a detailed comparison with the experiment. N evertheless, the calculations reproduce, semiquantitatively, the observatio ns. (C) 1999 American Institute of Physics. [S0021-9606(99)00446-8].