Hyper-Rayleigh scattering in the Fourier domain for higher precision: Correcting for multiphoton fluorescence with demodulation and phase data

An improved experimental technique for the suppression of the multiphoton f luorescence contribution in hyper-Rayleigh scattering experiments for the d etermination of the first hyperpolarizability of molecules in solution is p resented. This improvement allows for a better correction for the fluoresce nce artifact, so as to eliminate any overestimation for the value of the fi rst hyperpolarizability. The measurement of the demodulation only of the fl uorescence as a function of modulation frequency [Olbrechts , Rev. Sci. Ins trum. 69, 2233 (1998)] is now complemented by the measurement of the phase lag between the intermediate scattering and the time-delayed fluorescence. From the simultaneous data reduction of demodulation and phase shift toward the hyperpolarizability, fluorescence contribution, and fluorescence lifet ime, an improvement in precision of 1 order of magnitude is demonstrated. T his level of precision has been used to show the relative impact of f-orbit al filling and ligands on the molecular second-order nonlinear optical resp onse of lanthanide complexes containing a hemicyanine chromophore. (C) 2001 American Institute of Physics.