The electro-optical response of colloidal dispersions of rod-shaped gold particles is studied for various aspect
ratios (2.6 < L/d < 49; d = 15 nm) by monitoring the absorbance spectra in the visible wavelength regime.
The absorbance spectra strongly depend on the degree of orientational order of the rods and the direction of
the polarization of the incident light with respect to the applied electric field. From the change in absorbance
of the transverse resonance the electro-optical effect is deduced: at low electric field strengths a linear
dependence on the squared electric field strength is observed, and at sufficiently high electric field strengths
saturation occurs. This is in agreement with electro-optical theory. With increasing length, the anisotropy in
electric polarizability increases from 6.10-30 F.m2 to 12.10-30 F.2. It is found that the anisotropy in electric
polarizability depends on the square root of the particle length.