We show that the third-order optical response of disordered linear J-aggregates can be calculated by considering only a limited number of transitions between (multi-) exciton states. We calculate the pump-probe absorption spectrum resulting from the truncated set of transitions and show that, apart from the blue wing of the induced absorption peak, it agrees well with the exact spectrum.
Klugkist, J. A., Malyshev, V. A., & Knoester, J. (2008). Selection of dominant multi-exciton transitions in disordered linear J-aggregates. Journal of Luminescence, 128(5-6), 945-947. https://doi.org/10.1016/j.jlumin.2007.11.052