Dispersion of the phase response of dye solutions exposed to picosecond excitation

Tunable picosecond optical pulses were used to investigate the dispersion of the phase response of a solution of bleachable dye No. 3955, i.e., the frequency dependence of changes in the refractive index, that arises on exposure to high-intensity light as a result of changes in the populations of the ground and excited molecular states. In the wavelength range of the absorption band the refractive index of the solution increased as a result of bleaching, whereas in the fluorescence band it decreased. This agreed qualitatively with the predicted behavior.