THE DETERMINATION OF FIRST HYPERPOLARIZABILITIES-BETA USING HYPER-RAYLEIGH SCATTERING - A CAVEAT

A comparison of first hyperpolarizabilities beta determined by hyper-R ayleigh scattering (HRS; beta(HRS)) and electric field-induced second- harmonic generation(EFISH; beta(EFISH)) for a series of donor-acceptor substituted pi-conjugated organic compounds shows a marked discrepanc y between beta(HRS) and beta(EFISH) values for NLO-chromophores which fluoresce in the frequency-doubled wavelength region (532 nm). For MON S and DANS it is unequivocally established that two-photon absorption (TPA) at the fundamental wavelength (1064 nm) occurs followed by Stoke s and anti-Stokes fluorescence around the second-harmonic wavelength. Hence, hyper-Rayleigh scattering at 1064 nm is not suited to determini ng the beta of these fluorescent NLO-chromophores.