Coherent and incoherent dynamics of large molecules in solution studied on a 20 femtosecond time scale

Abstract

The ultrafast dynamics of dye molecules in solution was studied in temporally and spectrally resolved experiments on a 20 fs time scale. To separate the contributions form the ground and the excited states, a two-color scheme was employed. Blue pulses were used to excite a small fraction of the molecules to higher excited electronic states Sn (n>1) and the evolving dynamics was probed with red pulses tuned to the S0-S1 transition [1]. Around delay zero, a pronounced coherent signal occurs. The coherent coupling of the two electronic transitions is due to coherent vibrational motion in the S0 state induced by an impulsive Raman process. The molecules promoted to Sn states give rise to a fast ground state bleaching on a 50 fs time scale that is followed by the picosecond onset of stimulated emission from the S1 state.