COHERENT COUPLING EFFECTS IN PICOSECOND ABSORPTION EXPERIMENTS

Coherent picosecond-laser pulses that are used in absorption-relaxation measurements produce extraneous signal contributions for time-delays around zero via induced absorption gratings. A complete theory including pulse shape, population kinetics, polarization and orientational relaxation is given and discussed for different parameter values. The main result is that for parallel polarization of the interacting beams the transient-transmission signal is doubled at zero time-delay irrespective of population lifetime and rotational diffusion, while for perpendicular polarization rotational diffusion is strongly affecting the coherent signal contribution. Experimental results are given that illustrate the influence of different solute, solvent or laser pulse parameters on the coherent signals and agree very well with the theoretical description. © 1979 Springer-Verlag.