An instrument was constructed for studies of self diffusion of polymer in solution. The self diffusion coefficient, Ds, could be measured by using either of the fluorescence recovery after pattern photo-bleaching (FRAPP) or the forced Rayleigh scattering(FRS) techniques with slightly different experimental setups. These techniques are similar in parinciple. In both techniques, Ds is estimated from the relaxation process of intensity of light (fluorescence or diffracted light) due to

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... on after formation of grating-like pattern by photo-bleaching of polymers labeled with photo-bleachable dyes. Capability of the instrument was demonstrated from Ds measurements on solutions of two narrow distribution polystyrene samples with Ms=43,900 and 355,000 in dibutylphthalate in the range of polymer concentration from 1 to 50 wt%. The time variation of intensity of light from the two techniques , FRAPP and FRS, could be fitted with single exponential curves suitable for respective theoretical prediction. Values of Ds estimated with the two methods agreed with each other over the range of Ds values from 10-8 to 10-12 cm2/s