Femtosecond Photon Echoes in Molecular Aggregates Meier, Torsten Chernyak, V. Mukamel, S. Two-pulse four-wave-mixing signals from molecular aggregates, including effects of two-exciton states, static disorder, and exciton-phonon interaction represented by arbitrary spectral densities are calculated. Three types of contributions to the signal are identified. The first, reflecting exciton self-correlation, is similar to the photon echo from disordered two-level systems and dominates the signal for long time-delays. The second is related to correlations of one-exciton states, whereas the third reflects correlations between one- and two-exciton states. The information gained by completely resolving the signal field (both amplitude and phase) is analyzed using Wigner spectrograms. American Institute of Physics 1997 info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_6501 https://ris.uni-paderborn.de/record/43397 Meier T, Chernyak V, Mukamel S. Femtosecond Photon Echoes in Molecular Aggregates. <i>The Journal of chemical physics</i>. 1997;107(21):8759-8780. doi:<a href="https://doi.org/10.1063/1.475169">10.1063/1.475169</a> eng info:eu-repo/semantics/altIdentifier/doi/10.1063/1.475169 info:eu-repo/semantics/closedAccess