Three-pulse photon echo peak shift in optically dense samples

We have investigated the dependence of the three-pulse photon echo peak-shift (3PEPS) signal on solute concentration and sample path length. The most prominent effect is an increase of the amplitude of the long decay component of the 3PEPS at high optical densities, but signal distortions are observed for all timescales in the experiments. The distortions of the peak shift signal are more severe for longer path lengths. These observations are assigned to pulse propagation effects. At low concentrations interference between the solute signal and the non-resonant solvent response severely distort the peak profiles at short population times.