Four-wave mixing and luminescence of confined excitons in molecular aggregates and nanostructures. Many-body Green function approach

Four-wave mixing and spontaneous emission spectra of confined Frenkel excitons in molecular assemblies are calculated using a unified Green function approach. Applications to various time- and frequency-domain techniques show an interplay of coherent motion of two-exciton states and exciton transport in the third order response. Effect of exciton-phonon interactions and static disorder are studied. Many-body collective resonances which reflect level correlations and may not be attributed to specific pairs of eigenstates are predicted. A Kramers-Kronig representation of the nonlinear response in terms of a multidimensional spectral density offers a convenient computational scheme in condensed phases.