PICOSECOND PULSES FROM UV TO IR USING SPECTRO-TEMPORAL SELECTION DYE LASER

Abstract
Photophysical and photochemical properties of laser dyes (rhodamines and merocyanines) are studied through nanosecond and picosecond laser spectroscopy. The polarity of the dye molecule is one of the most important parameters. In the case of merocyanines, the dye solubility, the red or blue shift of the ground state S₀ absorption spectrum respectively for the less or more polar dyes, the large red shift of the fluorescence spectrum in polar solvents depend strongly on the dye polarity in its S₀ ground state but also in its fluorescent first singlet excited state S₁. Upon light excitation of DCM (4-dicyanomethylene-2-methyl-6-p-dimethylaminostyril-4H-pyran) a large change of the dipole moment from 5.6 D to 26.3 D is evidenced due to an intramolecular electron transfer from the electron donor amino-group to the electron acceptor cyanogroups.