Control of emission spectrum and excited-state dynamics in a cyanine dye molecule with femtosecond chirped pulses

Summary form only given. We could for the first time observe the dependence of the emission spectrum and excited-state dynamics in cyanine dye molecules on the chirp rate of the pump pulse. The fluorescence spectrum is expected to be dependent on the chirp rate as result of competition among the pump-dump configuration change associated with the vibrationally coupled modes, and vibration-vibration energy transfer. The chirp affects the branching ratio among these three processes, which can change the emission spectrum. The transient response of the excited state was also found to change drastically in a femtosecond pump-probe measurement. The dye molecule studied here is 3-3´-diethylthiatricarbocyanine iodide (DTTCI). We observed the remarkable dependence of the spectral shape of the emission and the excited-state population in DTTCI molecules on the pulse chirp. It was found for the first time that both the Raman gain-loss process of strongly coupled mode and the pump-dump mechanism change the spontaneous emission spectra, when the chirped pulse is used for excitation.