Coherent transients of virtual excitons in pseudoisocyanineJaggregates: Intermediate exciton-phonon interaction system

Abstract

We report the results of femtosecond pump-probe absorption spectroscopy under virtual excitation in pseudoisocyanine J aggregates. When the pump photon energy is lower than the J-band peak by one phonon energy, a resonant inverse Raman-type spectrum is observed. When the pump photon energy is tuned both below and above the inverse Raman resonance, the induced absorption peaks are observed only at the high-energy side of the J-band peak, namely, blueshifted dispersive spectra. The blueshifted spectra are ascribed to the nonresonant virtual excitons. The major character of the observed spectra agrees with a model calculation based on third-order nonlinear optical processes. The intermediate exciton-phonon coupling strength of pseudoisocyanine J aggregates enables us to observe an interplay of both a nonresonant virtual exciton contribution and a resonant inverse Raman contribution.