Observation of a thermal phase-grating contribution to diffraction in erythrosin-doped gelatin films

Dynamic laser-induced gratings were written into gelatin films doped with t he xanthene dye - erythrosin B. The diffraction signal relaxation time from the transient grating was analysed as a function of the pump beam fluence and grating period. Also, the relaxation time of the transient absorption s ignal was measured with a pump-probe technique to determine the triplet lif etime of the dye-host system. For writing beam fluences below 10 mJ/cm(2), the diffraction relaxation time was found to be half of the triplet lifetim e - consistent with a triplet-state population grating. However for fluence s above this, the diffraction relaxation time had a quadratic dependence up on the grating period, thus giving strong evidence for a thermal grating co ntribution to the diffraction signal. (C) 2000 Elsevier Science B.V. All ri ghts reserved.