Analysis of vibrational coherences in homodyne and two-dimensional heterodyne photon-echo spectra of Nile Blue

We propose a simple model which allows a comprehensive interpretation of the available experimental photon-echo data on Nile Blue. Homodyne signals such as two- and three-pulse photon echo, transient grating and three-pulse peak shift are addressed. An explanation of their time evolution is provided with a single parameter set. A new interpretation of two-dimensional (2D) heterodyne experimental spectra is proposed which emphasizes the strong electron-vibrational coupling of the 590 cm−1 mode of Nile Blue. The model is used for predictions of 2D correlation and relaxation signals monitored with improved resolution (low temperature, short pulse durations). It is argued that such measurements could provide the first experimental detection of the signatures of electron-vibrational coupling in 2D photon-echo spectra.