Strong-field approach to ultrafast pump-probe spectra: dye molecules in solution Original Research Article

The ultrafast dissipative dynamics of molecular vibrations under the influence of strong laser pulses is studied in the framework of the density matrix theory. To circumvent any perturbational treatment of the molecule-radiation coupling the related equations of motion are solved directly with the inclusion of the light field. The theory is applied to the simulation of 20 fs two-color pump-probe experiments on the laser-dye IR 125 [S.H. Ashworth, T. Hasche, M. Woerner, E. Riedle and T. Elsaesser, J. Chem. Phys. 104 (1996) 5761]. It can be demonstrated that a three-level model of a S0, a S1, and a higher excited Sn state completed by a single vibrational coordinate is sufficient to calculate the measured spectra. The main features of the spectra can be explained by the formation of a dynamical hole in the vibrational wave function of the electronic ground state. Its spatio-temporal oscillation and its dependence on the pump intensity is studied in detail.