Abstract

Results of femtosecond four-wave mixing (4-WM) measurements on several organic molecules in solution are reported. It is shown that a stochastic modulation model describes the two-pulse photon echo decay and the optical line shape very well. A multimode Brownian oscillator model provides a full description of these effects as well, and is also capable of predicting the Stokes shift of the emission within the same context. The dynamics of all systems studied (aprotic solutions) is found to occur in the intermediate modulation regime, where the amplitude (Δ) and inverse correlation time (Λ) of the Brownian oscillator are about equal: Δ|Λ≈1. Since for all systems studied, A is in the order of tens of THz, solvation is predicted to occur on a femtosecond time scale, in agreement with recently reported experiments.

© 1992 Optical Society of America