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

Abstract

An improved experimental technique for the suppression of the multiphoton fluorescence contribution in hyper-Rayleigh scattering experiments for the determination of the first hyperpolarizability of molecules in solution is presented. This improvement allows for a better correction for the fluorescence artifact, so as to eliminate any overestimation for the value of the first hyperpolarizability. The measurement of the demodulation only of the fluorescence as a function of modulation frequency [Olbrechts et al., Rev. Sci. Instrum. 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 lifetime, an improvement in precision of 1 order of magnitude is demonstrated. This level of precision has been used to show the relative impact of f-orbital filling and ligands on the molecular second-order nonlinear optical response of lanthanide complexes containing a hemicyanine chromophore.