Femtosecond photon-echo experiments on sodium resorufin in dimethylsulfoxide at room temperature show that optical dephasing in solution is of non-Markovian character. A single Gauss-Markov stochastic modulation process is used to interpret both the femtosecond light-scattering results and the steady-state absorption spectrum. The optical dynamics of this system appears to fall in the intermediate modulation regime. No evidence was found for contributions of slower dynamical processes to the absorption line breadth.

• Received 14 February 1991

DOI:https://doi.org/10.1103/PhysRevLett.66.2464