FEMTOSECOND HYPER-RAYLEIGH SCATTERING STUDY OF SPATIAL ORIENTATIONAL CORRELATIONS BETWEEN CHROMOPHORES

Since the introduction of Hyper-Rayleigh scattering (HRS) as a measure ment technique for the first hyperpolarizability of molecules in solut ion,(1) the importance of fluctuations was realized.(2) For isotropic solutions, a combination of the spatial and temporal orientational flu ctuations causes the instantaneous and local deviation from macroscopi c centrosymmetry, necessary to observe a second-order signal. The fluc tuations in the spatial orientational distribution function of nonline ar optical chromophores cause an HRS signal that fluctuates as a funct ion of position in solid samples. The correlation length, characterizi ng the decay of the autocorrelation function of this fluctuating signa l, indicates the degree of spatial correlation between these chromopho res. The development of femtosecond HRS was instrumental for the study of orientational correlations.(3)