We propose to perform femtosecond phase-locked stimulated photon echo and pump probe measurements on molecular aggregate systems at room temperature. The demonstrated high reliability of this techniques should allow for a careful analysis of the optical dephasing process. In this way a detailed picture is obtained of the exciton dynamics on the chain. In the optical response considered, properties of one and two exciton states are explicitly taken into account. With these photon echo experiments information on the solvation dynamics of non-localized states is also provided. These experiments are also relevant to a better understanding of energy transport in light-harvesting complexes. An essential part of this project is the realisation of a cavity-dumped femtosecond laser source based on a frequency-doubled Ti:sapphire laser that drives an optical parametric oscillator (OPO).