Femtosecond inverse Raman spectrum of molecular J‐aggregates

The femtosecond inverse Raman spectrum of J‐aggregates of a cyanine dye was studied theoretically and experimentally by the pump—probe experiment. The time dependence of the Raman signal intensity of the aggregates was fitted with an instantaneously responding component due to the Stark effect together with 200 fs and 1 ps lifetime components due to the excitons. The instantaneous response in the time‐resolved difference transmission spectrum including the inverse Raman, induced and saturated absorption was successfully reproduced by the calculation under sub‐resonant excitation based on the density matrix formalism.