Study of Domain Formation and Relaxation in Thin Polymeric Films by Femtosecond Hyper-Rayleigh Scattering

Femtosecond hyper-Rayleigh scattering has been used for probing the spatial orientational fluctuations between nonlinear optical chromophores as dopants in spin-coated polymer films. The fluctuation in the second-order incoherently scattered light intensity on microtranslation of the solid sample is indicative of the degree of spatial correlation between the chromophores. The decay of the autocorrelation function of this fluctuating signal corresponds to a spatial correlation length. Electric-field poling of dipolar chromophores increases this correlation length. The temporal characteristics of the correlation length were studied and compared with thermal relaxation times obtained with coherent second-harmonic generation. The correlation length decays much faster than that from the second-harmonic intensity. Possible implications of this fast relaxation are discussed.