The experimental setup used to perform hyper-Rayleigh scattering at the near infrared wavelength of 1907 nm is described. The setup described is employed to measure the first molecular hyperpolarizabilities, β, of three new thiophene-based nonlinear optical chromophores. Although scattering at this wavelength is weak and the experiment requires great care, use of it allows one to obtain near dispersion-free first hyperpolarizability. Comparing the results with those obtained on the same chromophores using the 1064 nm excitation, we show that the two state model, which is commonly used to relate the β values at different wavelengths, fails to correlate the results at these two excitation wavelengths.
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