Abstract
Dephasing‐induced resonances in the nonlinear optical response of molecular aggregates are expressed in terms of level correlations. The third‐order optical response is related to the three‐dimensional spectral density function χ(ε′, ε,ε″). Expressions for χ(ε′, ε,ε″) derived using the Frenkel exciton model show the existence of collective (dephasing‐induced) resonances.