FEMTOSECOND LASER FLUORESCENCE SPECTROSCO PY AND ULTRARAPID PHOTOPHYSICAL PROCESSES

In order to elucidate the dynamics of the relaxation processes of the DCM dye molecule in solution on the femtosecond time scale we have bui lt a time resolved fluorescence setup based on the upconversion method . The sum frequency generation of the fluorescence light and the delay ed laser pulses generated by a Ti-Sapphire oscillator was generated in a 0.2 mm BBO crystal. Time resolved fluorescence spectra (500-750 nm) were obtained by optimizing the phase matching angle of the crystal a nd by correcting the group velocity dispersion due to the lenses and f ilters. We present some experimental results about the DCM molecule in methanolic solution. They indicate a very fast red shift of the fluor escence spectrum in 170 fs after excitation followed by a slower relax ation with a 3.0 ps lifetime corresponding to the solvent reorganisati on around the fluorescent probe molecule.