Femtosecond hyper-Rayleigh scattering has been used to probe 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 individual chromophores. The decay of the autocorrelation function of this fluctuating signal is characterized by a spatial correlation length. Electric-field poling of dipolar chromophores is shown to increase this correlation length. The temporal characteristics of the correlation length have been studied and compared with thermal relaxation times obtained with coherent second-harmonic generation. The correlation length decays much faster than the second-harmonic intensity. Possible implications of this fast relaxation are addressed.
© 1998 Optical Society of America
(190.0190) Nonlinear optics : Nonlinear optics
(190.4710) Nonlinear optics : Optical nonlinearities in organic materials
(290.5870) Scattering : Scattering, Rayleigh
(320.2250) Ultrafast optics : Femtosecond phenomena
Geert Olbrechts, Erik J. H. Put, David Van Steenwinckel, Koen Clays, André Persoons, Celest Samyn, and Naoki Matsuda, "Study of domain formation and relaxation in thin polymeric films by femtosecond hyper-Rayleigh scattering," J. Opt. Soc. Am. B 15, 369-378 (1998)