Abstract

Recent attempts to determine the first nonlinear optical (NLO) hyperpolarizability (p) of a number of NLO organic chromophores from hyper-Rayleigh scattering (HRS) measurements have resulted in β-values much larger than those obtained from electric-field-induced second harmonic generation (EFISHG) measurements.^1,2 However, for compounds such as N,N Dimethylaminonitrostilbene (DANS) the NLO properties are expected to be essentially one dimensional and the two NLO characterization methods are expected to yield equivalent results. It has become apparent that the anomalous HRS results are due to two-photon-induced fluorescence from these molecules.^1,2 The "two-photon anti-Stokes" fluorescence overlaps the HRS spectrum and prevented the previous authors from making an accurate assessment of the scattered second harmonic intensity. With the use of a scanning monochromator in our HRS apparatus, we obtain results for p of fluorescent compounds from the HRS method that are in agreement with the results from the EFISHG experiment, as shown in Table 1. The HRS measurements were done at 1064 run with an acousto-optically Q- switched Nd:YAG laser (Quantronix 116) operating in a near-Gaussian TEM₀₀ mode. Tne input power level and penalization were selected by two Glan-Laser polarizers and a Soleil-Babinet compensator.

© 1996 Optical Society of America