Photoselection in picosecond differential absorption spectroscopy

The rate equations are used to study the kinetics of the induced bleaching and absorption in the case when the induced effects are measured with a low-intensity linearly polarized probe ultrashort pulse from the continuum and the orientation of the polarization vectors of the excitation and probe light pulses is either parallel or perpendicular. It is shown that the degree of photodichroism changes during the bleaching (induced absorption) process assuming a maximum value (governed by the optical density of a sample) at the beginning of the excitation pulse and a minimum value (dependent on the energy of the excitation pulse) at the end of the pulse or on attainment of complete inversion.